learn basic to advance C Programming Notes

C Programming Notes
What is Programming ?
Computer Programming is a medium for us to Communicate with
Computers
What is C?
C is a general-purpose programming language created by Dennis
Ritchie at the Bell Laboratories in 1972.
It is a very popular language, despite being old. The main reason for
its popularity is because it is a fundamental language in the field of
computer science.
Why Learn C?
● It is one of the most popular programming languages in the
world
● If you know C, you will have no problem learning other popular
programming languages such as Java, Python, C++, C#, etc,
as the syntax is similar
● C is very fast, compared to other programming languages, like
Java and Python
● C is very versatile; it can be used in both applications and
technologies
Variables
Variables are containers for storing data values, like numbers and
characters. It’s also the name of a memory location.
In C, there are different types of variables for example:
● int - stores integers (whole numbers), without decimals, such as
123 or -123
● float - stores floating point numbers, with decimals, such as 19.99
or -19.99
Written By : Akshay Bhagade

● Double - stores floating point numbers, with decimals, such as
19.99 or -19.99
● char - stores single characters, such as 'a' or 'B'. Characters are
surrounded by single quotes
E.g. int num = 34, float number = 45.7, char name = ’A’
The general rules for naming variables are:
● Names can contain letters, digits and underscores
● Names must begin with a letter or an underscore (_)
● Names are case-sensitive (myVar and myVar are different
variables)
● Names cannot contain whitespaces or special characters like !,
#, %, etc.
● Reserved words (such as int) cannot be used as names
Basic Data Types
The data type specifies the size and type of information the variable
will store.
Data
Type
Size Description Exam
ple
int 2 or 4
bytes
Stores whole numbers, without decimals 1
float 4 bytes Stores fractional numbers, containing one
or more decimals. Sufficient for storing
6-7 decimal digits
1.99
double 8 bytes Stores fractional numbers, containing one
or more decimals. Sufficient for storing
15 decimal digits
1.99
char 1 byte Stores a single character/letter/number,
or ASCII values
'A'

Format Specifiers
Format specifiers are used together with the printf() function to tell
the compiler what type of data the variable is storing. It is basically
a placeholder for the variable value.
Data Type Format Specifiers
● int %i or %d
● float %f
● double %lf or %f
● char %c
Keywords
These are reserved words,whose meaning is already known to the
compiler there are 32 keywords available in C
Auto double int struck
Break long else switch
Case return enum typedef
Char register extern union
Const short float unsigned
Continue signed for void
Default size of goto volatile
Do static if while

OUR FIRST C PROGRAM
#include <stdio.h>
int main() {
printf("Hello, I am Learning C Programming");
return 0;
}
BASIC STRUCTURE OF A C PROGRAMMING
Line 1: #include <stdio.h> is a standard input output header file library
that lets us work with input and output functions, such as printf() (used in
line 4). Header files add functionality to C programs.
Line 2: The int keyword indicates that the main function will return an
integer value. By convention, returning 0 indicates that the program
terminated successfully.
main(). This is called a function. Any code inside its curly brackets {} will be
executed.
Line 3: printf() is a function used to output/print text to the screen. In
our example, it will output "Hello, I am Learning C with Harry".
Line 4: return 0 ends the main() function.
Line 5: Do not forget to add the closing curly bracket } to actually end the
main function.
Note that: Every C statement ends with a semicolon ;
COMMENTS
Comments are used to clarify something about the program in plain
language.it is a way for us to add notes to our program.there are
two types of comments in C
1. Single line comment : //This is a comment
2. Multi line comment : /* This is a multi
line comment *
Comments in a C program are not executed and ignored

Receiving input from the user
In order to take input from the user and assign it to a variable, we
use scanf() function.
Syntax for using scanf ;
#include <stdio.h>
int main() {
int number;
printf("Enter a number: ");
scanf("%d", &number);
printf("You entered: %dn", number);
return 0;
}
Note: & is important
& is the “address of” operator and it means that the supplied value
should be copied to the address which is indicated by variable i.
CHAPTER 1- PRACTICE SET
Q1. Write a c program to calculate area of a rectangle
(a) Using hard coded inputs
(b) Using inputs supplied by the user
Q2. Calculate the area of a circle and modify the same program to
calculate the circumference of the circle.
Q3. Write a program to convert celsius (Centigrade degree
temperature to fahrenheit)

Chapter 2- INSTRUCTIONS AND OPERATORS
Operators are used to perform operations on variables and values.
Types of Operator:
● Arithmetic operators
● Assignment operators
● Comparison operators
● Logical operators
● Bitwise operators
Arithmetic Operators
Arithmetic operators are used to perform common mathematical operations.
Operator Name Description Example
+ Addition Adds together two values x + y
- Subtraction Subtracts one value from
another
x - y
* Multiplication Multiplies two values x * y
/ Division Divides one value by another x / y
% Modulus Returns the division remainder x % y
++ Increment Increases the value of a variable
by 1
++x
-- Decrement Decreases the value of a
variable by 1
--x

Assignment Operators
Assignment operators are used to assign values to variables.
Operator example Same as
= x = 5 x = 5
+= x += 3 x = x + 3
-= x -= 3 x = x - 3
*= x *= 3 x = x * 3
/= x /= 3 x = x / 3
Comparison Operators
Comparison operators are used to compare two values (or variables). This
is important in programming, because it helps us to find answers and
make decisions.
The return value of a comparison is either 1 or 0, which means true (1) or
false (0). These values are known as Boolean values.
Operator Name Example Description
== Equal Equal to x == y Returns 1 if the values are
equal
!= Not equal x != y Returns 1 if the values are
not equal
> Greater than x > y Returns 1 if the first value
is greater than the second
value

< Less than x < y Returns 1 if the first value
is less than the second
value
>= Greater than or
equal to
x >= y Returns 1 if the first value
is greater than, or equal
to, the second value
<= Less than or
equal to
x <= y Returns 1 if the first value
is less than, or equal to,
the second value
Logical Operators
You can also test for true or false values with logical operators.
Operator Name Example Description
&& Logical and x < 5 && x < 10 Returns 1 if both statements are
true
|| Logical or x < 5 || x < 4 Returns 1 if one of the
statements is true
! Logical not !(x < 5 && x <
10)
Reverse the result, returns 0 if
the result is 1
Booleans
Very often, in programming, you will need a data type that can only have
one of two values, like:
● YES / NO
● ON / OFF
● TRUE / FALSE
A boolean variable is declared with the bool keyword and can only take
the values true or false:
● 1 (or any other number that is not 0) represents true
● 0 represents false

Chapter 3- Conditional Statements
The conditional statements are also known as Decision-Making
Statements and are used to evaluate one or more conditions and make
the decision whether to execute a set of statements or not. These
decision-making statements in programming languages decide the
direction of the flow of program execution.
● Conditional Operator (? :)
● If Statement
● If-else statement
● Ladder else-if statement
● Nested if-else statement
● Switch statement
Conditional Operator/Ternary Operator (? :)
Syntax:
(condition) ? Execute when condition true : Execute when condition false;
Example:
1) print the greater number between two numbers
#include <stdio.h>
int main() {
int a,b;
printf("enter a: ");
scanf("%d",&a);
printf("enter b: ");
scanf("%d",&b);
a>b ? printf("a is greater"): printf("b is greater");
return 0;
}

Output :
enter a: 13
enter b: 23
b is greater
2) Check the number is positive or negative
#include <stdio.h>
int main() {
int number;
printf("enter number: ");
scanf("%d",&number);
number > 0 ? printf("Number is Positive"): printf("Number is Negative");
return 0;
}
Output :
enter number: 23
Number is Positive
If Statement
if a certain condition is true then a block of statements is executed
otherwise not.
Syntax :
if(condition)
{
// Statements to execute if
// condition is true
}

Example:
1)
#include <stdio.h>
int main() {
if (20 > 18) {
printf("20 is greater than 18");
}
return 0;
}
Output :
20 is greater than 18
2)
#include <stdio.h>
int main() {
int x = 20;
int y = 18;
if (x > y) {
printf("x is greater than y");
}
}
Output :
x is greater than y
If-Else Statement
if a certain condition is true then a if block of statements is executed if
condition false then else block will be executed.
Syntax :
if (condition) {
// block of code to be executed if the condition is true
} else {
// block of code to be executed if the condition is false
}

Example:
1) print the greater number between two numbers
#include <stdio.h>
int main() {
int a,b;
printf("enter a: ");
scanf("%d",&a);
printf("enter b: ");
scanf("%d",&b);
if(a > b){
printf("a is greater");
}else{
printf("b is greater");
}
return 0;
}
Output :
enter a: 23
enter b: 34
b is greater
2) Enter the percentage and check whether the student is pass or fail?
#include <stdio.h>
int main() {
int percentage ;
printf("enter total percentage: ");
scanf("%d",&percentage);
if(percentage >= 35){
printf("Student is Pass");
}else{
printf("Student is Fail");
}
return 0;
}

Output :
enter total percentage: 35
Student is Pass
More Questions :-
3) Enter the number and check whether the number is positive or
negative.
4) Enter the number and check whether the number is even or odd.
5) Enter the year and check whether it is Leap year or Not.
6) Enter the purchase and sold amount and declare whether the profit or
loss happened.
7) Enter the age to check if the person is eligible for voting or not.
Ladder If-Else-if Statement
The if else if statements are used when the user has to decide
among multiple options.
if a certain condition is true then the particular block of statements
is executed If none of the conditions is true, then the final else
statement will be executed.
Syntax :
if (condition1) {
// Code to execute if condition1 is true
}
else if (condition2) {
// Code to execute if condition1 is false and condition2 is true
}
else if (condition3) {
// Code to execute if condition1 and condition2 are false, and condition3 is
true
}
else {
// Code to execute if all above conditions are false
}

Example:
1) Take input from the user and print the number is positive or negative
or zero.
#include <stdio.h>
int main() {
int number;
printf("enter number: ");
scanf("%d",&number);
if(number > 0){
printf("you enter positive number...");
}
else if(number < 0){
printf("you enter negative number...");
}
else{
printf("you enter the zero...");
}
return 0;
}
Output :
enter number: 0
you enter the zero…
enter number: -8
you enter negative number...
enter number: 12
you enter positive number...

2) Write a program to find the maximum between three number
#include <stdio.h>
int main() {
int a, b, c;
// Get input from the user
printf("Enter three numbers: n");
scanf("%d",&a);
scanf("%d",&b);
scanf("%d",&c);
if(a > b && a > c ){
printf("%d is Greater...",a);
}
else if(b > a && b > c ){
printf("%d is Greater...",b);
}
else{
printf("%d is Greater...",c);
}
return 0;
}
Output :
Enter three numbers:
45
23
56
56 is Greater...
More Questions :-
3) Build the Calculator.
4) Write a c program to input marks of five subjects eng,hindi,mar,maths,
phy, calculate percentage and print grade according to the following.
- Grade Merit — > percentage in between 90-100.
- Grade Distinction — > percentage in between 75-90.
- Grade First Class— > percentage in between 60-75.
- Grade Second Class— > percentage in between 45-60.
- Grade Pass— > percentage in between 35-45.
- Fail — > percentage less than 35.

Nested If-Else Statement
A nested if-else statement is an if statement inside another if statement.
The general syntax of nested if-else statement in C is as follows:
Syntax :
if (condition1) {
/* code to be executed if condition1 is true */
if (condition2) {
/* code to be executed if condition is true */
} else {
/* code to be executed if condition is false */
}
} else {
/* code to be executed if condition1 is false */
}
Example:
1) Check the given number is positive or negative or zero. If the number
is positive then the check number is even or odd..
#include <stdio.h>
int main() {
int num = 7;
if (num > 0) {
printf("The number is positive.n");
if (num % 2 == 0) {
printf("The number is even.n");
} else {
printf("The number is odd.n");
}
} else {
if (num < 0) {
printf("The number is negative.n");
} else {
printf("The number is zero.n");
}
}
return 0;
}

Output :
The number is positive.
The number is odd.
Switch Statement
Switch case statement evaluates a given expression and based on the
evaluated value(matching a certain condition), it executes the statements
associated with it. Basically, it is used to perform different actions based
on different conditions(cases).
Rules of the switch case statement
Following are some of the rules that we need to follow while using the
switch statement:
1. In a switch statement, the “case value” must be of “char” and
“int” type.
2. There can be one or N number of cases.
3. The values in the case must be unique.
4. Each statement of the case can have a break statement. It is
optional.If there is no break statement found in the case, all the
cases will be executed present after the matched case.
5. The default Statement is also optional.
Syntax :
switch(expression){
case value1:
//code to be executed;
break;
case value2:
//code to be executed;
break;
......
default:
code to be executed if all cases are not matched;
}

Example:
1) print the value of the given number using the switch statement.
#include <stdio.h>
int main() {
int num = 2;
switch (num) {
case 1:
printf("Value is 1n");
break;
case 2:
break;
case 3:
break;
default:
printf("Value is not 1, 2, or 3n");
break;
}
return 0;
}
Output :
Value is 2
2) Write a c program to input the day number and print week day.
#include <stdio.h>
int main()
{
int day = 2;
switch (day) {
case 1:
printf("Monday");
break;

case 2:
printf("Tuesday");
break;
case 3:
printf("Wednesday");
break;
case 4:
printf("Thursday");
break;
case 5:
printf("Friday");
break;
case 6:
printf("Saturday");
break;
case 7:
printf("Sunday");
break;
default:
printf("Invalid Input");
break;
}
return 0;
}
Output :
Tuesday
3) enter an alphabet and check whether it is vowel or consonant.
4) write a c program to input a month number and print no of days in that
month.

Chapter 4-Loops in C
Loops in programming are used to repeat a block of code until the
specified condition is reached. A loop statement allows programmers to
execute a statement or group of statements multiple times without
repetition of code.
● For Loop
● While Loop
● Do While Loop
● Nested For Loop
for Loop
for loop in C programming is a repetition control structure
that allows programmers to write a loop that will be executed a
specific number of times.
Syntax :
#include <stdio.h>
int main()
{
for (initialization; condition; increment/decrement){
// statements inside the body of loop
}
return 0;
}
Example : 1) print the 1 to 10 number.
#include <stdio.h>
int main() {
int i;
for (i = 1; i <= 10; i++)
{
printf("%d ", i);
}
return 0;
}

Output :
1 2 3 4 5 6 7 8 9 10
More Questions :-
1) print the sum of n natural number
2) print the factorial.
3) write a c program to print all even numbers between 1 to 100.
4) write a program to print a multiplication table of any number.
5) print Fibonacci Series.
While Loop
Syntax :
#include <stdio.h>
int main() {
// Initialization
while (condition) {
statement
increment/decrement
}
return 0;
}
Example :
1) print the 1 to 10 number.
#include <stdio.h>
int main() {
int i = 1;
while (i <= 10) {
printf("%d", i);
i++;
}
return 0;
}
Output :
1 2 3 4 5 6 7 8 9 10

More Questions :-
1) print Fibonacci Series.
2) All the above question of for loops
Mid/Hard Level Questions :-
1) Take 10 numbers from the user and count how many there are
positive, negative and zero numbers.
2) print the sum of digits.If number is 56 then answer is 11 (5+6=11)
3) write a c program to check if a given number is prime or not.
4) print the reverse number for e.g. number is 156 then output is 651
5) Check the entered number is palindrome or not.
Do-while Loop
do/while will always be executed at least once, even if the condition
is false, because the code block is executed before the condition is
checked.
Syntax :
#include <stdio.h>
int main() {
// Initialization
do {
statement
increment/decrement
} while (condition);
return 0;
}
Example :
#include <stdio.h>
int main() {
int i = 1;
do {
printf("%d n", i);
i++;
}while (i <= 10);
return 0;
}

Output :
1 2 3 4 5 6 7 8 9 10
Nested for Loop
loop inside another loop. This is called a nested loop. The "inner
loop" will be executed one time for each iteration of the "outer loop"
Example :
#include <stdio.h>
int main() {
int i, j;
// Outer loop
for (i = 1; i <= 2; i++) {
printf("Outer: %dn", i);
// Inner loop
for (j = 1; j <= 3; j++) {
printf(" Inner: %dn", j);
}
}
return 0;
}
Output :
Outer: 1
Inner: 1
Inner: 2
Inner: 3
Outer: 2
Inner: 1
Inner: 2
Inner: 3

Star Pattern Questions :-
1
1 2
1 2 3
1 2 3 4
1 2 3 4 5
Number left
half pyramid
*
* *
* * *
* * * *
* * * * *
left half
pyramid
* * * * *
* * * *
* * *
* *
*
Inverted left
half pyramid
*
* *
* * *
* * * *
* * * * *
right half
pyramid
* * * * *
* * * *
* * *
* *
*
inverted
right half
pyramid
1
2 3
4 5 6
7 8 9 10
11 12 13 14 15
floyd's
triangle
*****
* *
* *
* *
*****
hollow
rectangle;
1
0 1
1 0 1
0 1 0 1
1 0 1 0 1
triangle 1_0
******
******
******
******
******
solid rhombus
1
2 2
3 3 3
4 4 4 4
5 5 5 5 5
Num pyramid
Advance Pattern :
*
***
*****
*******
*********
*********
*******
*****
***
*
diamond pattern
* *
** **
*** ***
**** ****
**********
**********
**** ****
*** ***
** **
* *
butterfly Pattern
Jump Statements :-
- Break
- Continue

Break :-
The break statement can also be used to exit from a loop.
Example :
#include <stdio.h>
int main() {
int i;
for (i = 0; i < 10; i++) {
if (i == 4) {
break;
}
printf("%d", i);
}
return 0;
}
Output :
0123
Continue:-
The continue statement skips one iteration (in the loop) if a specified
condition occurs, and continues with the next iteration in the loop.
Example :
#include <stdio.h>
int main() {
int i;
for (i = 0; i < 10; i++) {
if (i == 4) {
continue;
}
printf("%d ", i);
}
return 0;
}
Output :
0 1 2 3 5 6 7 8 9

Chapter 5 - Arrays
Arrays are used to store multiple values in a single variable, instead
of declaring separate variables for each value. similar data items
stored in contiguous memory locations.
It can be used to store the collection of primitive data types such as
int, char, float, etc., and also derived and user-defined data types
such as pointers, structures, etc.
Syntax:
data_type array_name [size];
data_type array_name [size] = {value1, value2, ... valueN};
It is possible to initialize an array during declaration. For example,
int mark[5] = {46, 87, 81, 74, 90};
You can also initialize an array like this.
int mark[] = {46, 87, 81, 74, 90};
Example :
#include <stdio.h>
int main() {
int myNumbers[] = {46, 87, 81, 74, 90};
printf("%d", myNumbers[0]);
return 0;
}
Output :
46

Change an Array Element
To change the value of a specific element, refer to the index number:
#include <stdio.h>
int main() {
int myNumbers[] = {46, 87, 81, 74, 90};
myNumbers[0] = 66;
printf("%d", myNumbers[0]);
return 0;
}
Output :
66
Array with For loop
Also we caṇ print array elements with the for loop.
#include <stdio.h>
int main() {
int myNumbers[] = {46, 87, 81, 74, 90};
int i;
for(i = 0; i < 4; i++) {
printf("%dn", myNumbers[i]);
}
return 0;
}
Output :
46
87
81
74
90

Another common way to create arrays, is to specify the size of the
array, and add elements later:
#include <stdio.h>
int main() {
// Declare an array of four integers:
int myNumbers[4];
// Add elements to it
myNumbers[0] = 46;
myNumbers[1] = 87;
myNumbers[2] = 81;
myNumbers[3] = 74;
myNumbers[4] = 90;
printf("%dn", myNumbers[2]);
return 0;
}
Output :
81
Get Array Size or Length
#include <stdio.h>
int main() {
int myNumbers[] = {46, 87, 81, 74, 90};
printf("%d", sizeof(myNumbers));
return 0;
}
Output: 20 - It is because the sizeof operator returns the size of a type in
bytes.
- for calculating size of array divides the size of the array by the size of
one array element.

calculating size of array:
#include <stdio.h>
int main() {
int myNumbers[] = {46, 87, 81, 74, 90};
int length = sizeof(myNumbers) / sizeof(myNumbers[0]);
printf("%d", length);
return 0;
}
Output :
5
Using for loop when we don't know the size of an array:
#include <stdio.h>
int main() {
int myNumbers[] = {46, 87, 81, 74, 90};
int length = sizeof(myNumbers) / sizeof(myNumbers[0]);
int i;
for (i = 0; i < length; i++) {
printf("%dt", myNumbers[i]);
}
return 0;
}
Output :
46 87 81 74 90

Input Array From User:
Q. Program to take 5 values from the user and store them in an array
#include <stdio.h>
int main() {
int values[5];
printf("Enter 5 integers: ");
// taking input and storing it in an array
for(int i = 0; i < 5; i++) {
scanf("%d", &values[i]);
}
printf("Displaying integers: ");
// printing elements of an array
for(int i = 0; i < 5; i++) {
printf("n%d", values[i]);
}
return 0;
}
Output :
Enter 5 integers: 45
87
67
98
45
Displaying integers:
45
87
67
98
45

Questions:
1) Enter an array and take any input number from the user and check
whether the number exists in the array or not.
2) Enter an array and find the minimum number in that array.
3) Enter an array and find the maximum number in that array.
4) Program to find the sum and average of n numbers using arrays.
5) Sorting an array.
2D Arrays:
A multidimensional array is basically an array of arrays.
If you want to store data as a tabular form, like a table with rows and
columns, Then we use multidimensional arrays.
E.g.
int matrix[3][3] = {};
E.g.
int matrix[2][3] = { {1, 4, 2}, {3, 6, 8} };

Example:
#include <stdio.h>
int main() {
int matrix[2][3] = { {1, 4, 2}, {3, 6, 8} };
printf("%d", matrix[0][2]);
return 0;
}
Output :
2
How To Change 2D Array Element:
#include <stdio.h>
int main() {
int matrix[2][3] = { {1, 4, 2}, {3, 6, 8} };
matrix[0][0] = 9;
printf("%d", matrix[0][0]); // Now outputs 9 instead of 1
return 0;
}
Output :
9

Print 2D Array Element By Using Loop:
#include <stdio.h>
int main() {
int matrix[2][3] = { {1, 4, 2}, {3, 6, 8} };
int i, j;
for (i = 0; i < 2; i++) {
for (j = 0; j < 3; j++) {
printf("Element at x[%i][%i]: ", i, j);
printf("%dn", matrix[i][j]);
}
}
return 0;
}
Output :
Element at x[0][0]: 1
Taking Array Elements from User and print the array
#include <stdio.h>
int main() {
int arr[3][3],i,j;
// taking user input
for(i=0;i<3;i++){
for(j=0;j<3;j++){
printf("Enter the Elements [%d][%d]: ",i,j);

scanf("%d",&arr[i][j]);
}
}
printf("nPrinting The Element......n");
for(i=0;i<3;i++){
for(j=0;j<3;j++){
printf("%dt",arr[i][j]);
}
printf("n");
}
return 0;
}
Output :
Enter the Elements [0][0]: 34
Printing The Element......
34 67 34
9 86 12
45 67 34
Questions:
1) Enter an 2D array and take any input number from the user and check
whether the number exists in the array or not.
2) Addition Of Two Matrices
3) Multiplication of Two Matrix
4) Sum of Diagonal Elements in Square Matrix.

Chapter 6 - Strings
A String in C programming is a sequence of characters terminated
with a null character ‘0’. The C String is stored as an array of
characters. The difference between a character array and a C string
is that the string in C is terminated with a unique character ‘0’.
Note: %s is the format specifier to print a string in C.
Syntax:
char variableName[size];
For example:
char name[] = "c string";
When the compiler encounters a sequence of characters enclosed in
the double quotation marks, it appends a null character 0 at the
end by default.
There are two methods to do this:
1) Using Char Array -
without declaring the size of the array
char str[] = {'C', 'o', 'm', 'p', 'u', 'f', 'i', 'e', 'l', 'd', '0'};
by declaring the size of the array
char str[11] = {'C', 'o', 'm', 'p', 'u', 'f', 'i', 'e', 'l', 'd', '0'};
2) Using String Literal -
without declaring the size of the array
char str[]="Compufield";
by declaring the size of the array
char str[11]="Compufield";

Example :
#include <stdio.h>
int main() {
char str[11] = {'C', 'o', 'm', 'p', 'u', 'f', 'i', 'e', 'l', 'd', '0'};
char str1[11] = "Compufield";
printf("String by char array method: %sn", str);
printf("String by String Literal method: %sn", str1);
return 0;
}
Output :
String by char array method: Compufield
String by String Literal method: Compufield
Accessing The String:
As the string is array of characters, we can access the characters of the
string with their index number. The string index starts with 0.
%c is a format specifier to print a single character.
Example :
#include <stdio.h>
int main() {
printf("%c", str[5]);
return 0;
}
Output :
f

Modify The String:
To change the value of a specific character in a string, refer to the index
number, and use single quotes:
Example :
#include <stdio.h>
int main() {
char str[]="HelloWorld";
str[4] = 'i';
printf("%s", str);
return 0;
}
Output :
HelliWorld
Loops Through String:
We can also loop through the characters of a string, using a for loop:
Example :
#include <stdio.h>
int main() {
int length = sizeof(str) / sizeof(str[0]);
for (int i = 0; i < length; i++) {
printf("%cn", str[i]);
}
return 0;
}
Output :

Take Input String from User:
1) Using scanf()
Example :
#include <stdio.h>
int main()
{
char name[20];
printf("Enter name: ");
scanf("%s", name);
printf("Your name is %s", name);
return 0;
}
Output :
Enter name: Gaurav Therade
Name: Gaurav.
Note:
The scanf() function reads the sequence of characters until it encounters
whitespace (space, newline, tab, etc.).
#include <stdio.h>
int main()
{
char name[30];
printf("Enter name: ");
fgets(name, sizeof(name), stdin); // read string
printf("Name: ");
puts(name); // display string
return 0;
}
Output :
Enter name: Gaurav Therade
Name: Gaurav Therade

String Functions in C:
There are many important string functions defined in "string.h" library.
No. Function Description
1) strlen(string_name) returns the length of the string name.
2) strcpy(destination,
source)
copies the contents of source string to
destination string.
3) strcat(first_string,
second_string)
concats or joins first string with second string.
The result of the string is stored in first string.
4) strcmp(first_string,
second_string)
compares the first string with second string. If
both strings are same, it returns 0.
5) strrev(string) returns reverse string.
6) strlwr(string) returns string characters in lowercase.
7) strupr(string) returns string characters in uppercase.
Example :
1) find the length of string
#include <stdio.h>
#include <string.h>
int main() {
char str1[] = "Compufield";
char str2[20];
printf("Length of str1: %dn", strlen(str1));
return 0;
}
Output :
Length of str1: 10

Example :
2) copy string from another string
#include <stdio.h>
#include <string.h>
int main() {
char str1[20] = "C programming";
char str2[20];
// copying str1 to str2
strcpy(str2, str1);
puts(str2); // C programming
return 0;
}
Output :
C programming
Example :
3) concatenate string
#include<stdio.h>
#include <string.h>
int main(){
char ch1[10]="Hellot";
char ch2[10]="World";
strcat(ch1,ch2);
printf("%s",ch1);
return 0;
}
Output :
Hello World
Example :
4) Compared Strings
#include <stdio.h>
#include <string.h>
int main() {

char str1[20], str2[20];
printf("Enter 1st string: ");
fgets(str1, sizeof(str1), stdin);
printf("Enter 2nd string: ");
fgets(str2, sizeof(str2), stdin);
if (strcmp(str1, str2) == 0) {
printf("Strings are equaln");
} else {
printf("Strings are not equaln");
}
return 0;
}
Output :
Enter 1st string: hello
Enter 2nd string: hello
Strings are equal
Example :
5) Reverse the Strings
#include<stdio.h>
#include <string.h>
int main(){
char str[20];
printf("Enter string: ");
gets(str);
printf("String is: %s",str);
printf("nReverse String is: %s",strrev(str));
return 0;
}
Output :
String is: dog
Reverse String is: god

Example :
6) Convert Strings into Lowercase & Uppercase
#include<stdio.h>
#include <string.h>
int main(){
char str[20]= "CompuField";
printf("String is: %s",str);
printf("nLower String is: %s",strlwr(str));
printf("nUpper String is: %s",strupr(str));
return 0;
}
Output :
String is: CompuField
Lower String is: compufield
Upper String is: COMPUFIELD
Questions :
1) reverse the string without using the rev function.
2) Check if the string is palindrome or not.
3) Write a program in C to count the total number of words in a string.
4) Write a program in C to count the total number of alphabets, digits and
special characters in a string.
5) Write a program in C to count the total number of vowels or
consonants in a string.
6) Write a C program to sort a string array in ascending order.
7) Write a program in C to find the frequency of characters.

Chapter 7 - Functions
A function is a block of code that performs a specific task when a
function is called. They provide a way to break down a program into
smaller, manageable units, which makes the code more readable,
reusable, and maintainable. They are of two types: Built-in and User
Defined.
types of Functions:
Built in Functions: are the functions which are declared in the C header
files such as scanf(), printf(), gets(), puts(), sqrt(), pow () etc.
User-defined functions: are the functions which are created by the C
programmer, so that he/she can use it many times. It reduces the
complexity of a big program and optimises the code.
They are of two types of user-defined function;
1. Function with a return value
2. Function without a return value (void functions)

Function without Return value:
1) Print name using function
#include<stdio.h>
// Function Declaration
void printName();
int main ()
{
printf("Hello ");
printName(); // Function Call
return 0;
}
// Function Definition
void printName()
{
printf("Ruhi");
}
Output :
Hello Ruhi
2) Print name using function with parameter/Arguments.
#include <stdio.h>
void greet(char name[]);
int main()
{
greet("Ekayaa"); // Function Call
return 0;
}
void greet(char name[])
{
printf("Hello, %s!", name);
}
Output :
Hello, Ekayaa!

3) Sum of two number
#include<stdio.h>
void sum(); // Function Declaration
int main() // main method
{
printf("ncalculate the sum of two numbers:");
sum(); // Function call in main method
return 0;
}
void sum() // Function Definition
{
int a,b;
printf("nEnter two numbers: ");
scanf("%d %d",&a,&b);
printf("The sum is: %d",a+b);
}
Output :
Enter two numbers: 23 67
The sum is: 90
Function with return value:
1) Sum of two number
#include <stdio.h>
int add(int a, int b);
int main()
{
int result = add(8, 9); //Function call
printf("The sum of a + b = %dn", result);
return 0;
}
int add(int a, int b)
{
return a + b;
}
Output :
The sum of a + b = 17

Multiple Parameters
Inside the function,we can add as many parameters
#include <stdio.h>
void myFunction(char name[], int age) {
printf("Hello %s. You are %d years oldn", name, age);
}
int main() {
myFunction("Akaay", 3);
myFunction("Driti", 14);
myFunction("Gaurav", 30);
return 0;
}
Output :
Hello Akaay. You are 3 years old
Hello Driti. You are 14 years old
Hello Gaurav. You are 30 years old
You can also pass arrays to a function:
#include <stdio.h>
void myFunction(int myNumbers[5]) {
for (int i = 0; i < 5; i++) {
printf("%dn", myNumbers[i]);
}
}
int main() {
int myNumbers[5] = {10, 20, 30, 40, 50};
myFunction(myNumbers);
return 0;
}

Questions :
1) Write a program in C to swap two numbers using a function.
2) Write a program in C to check if a given number is even or odd using
the function.
3) Write a program in C to find the sum of the series
4) program to calculate the average of five numbers.
5) Convert Celsius to Fahrenheit
6) print the factorial using a function.
Maths Function:
There is also a list of maths functions available, that allows you to
perform mathematical tasks on numbers.To use them, you must include
the math.h header file in your program:
1) To find the square root of a number, use the sqrt() function:
#include <stdio.h>
#include <math.h>
int main() {
printf("%f", sqrt(16));
return 0;
}
Output :
4.000000
2) The pow() function returns the value of x to the power of y (xy):
#include <stdio.h>
#include <math.h>
int main() {
printf("%f", pow(4, 3));
return 0;
}
Output :
64.000000

Recursion :
Recursion is the technique of making a function call itself. This
technique provides a way to break complicated problems down into
simple problems which are easier to solve.
Question:
1) print the number of 1 to 5 and also reverse order using recursion.
#include <stdio.h>
void printnum(int n) {
if (n == 6) {
return;
}
printf("%dt", n);
printnum(n + 1);
}
int main() {
int n = 1;
printnum(n);
return 0;
}
Output :
1 2 3 4 5
2) calculate sum of n natural numbers using recursion.
#include <stdio.h>
// Function prototype
void printsum(int i, int n, int sum);
int main() {
int num;
printf("Enter the number: ");
scanf("%d", &num);
printsum(1, num, 0);
return 0;
}

void printsum(int i, int n, int sum) {
if (i == n) {
sum += i;
printf("sum is: %dn", sum);
return;
}
sum += i;
printsum(i + 1, n, sum);
}
Output :
Enter the number: 5
sum is: 15
3) find the factorial by using recursion.
#include <stdio.h>
// Recursive function
int printfact(int n) {
if (n == 1 || n == 0) {
return 1;
}
int fact_1 = printfact(n - 1);
int fact_2 = n * printfact(n - 1);
return fact_2;
}
int main() {
int num;
printf("Enter the number: ");
scanf("%d", &num);
int result = printfact(num);
printf("Factorial of %d is %dn", num, result);
return 0;
}
Output :
Enter the number: 5
Factorial of 5 is 120

Chapter 8 - C Structures
A structure is a container to store multiple types of variables. The
variables stored in a structure are called member variables. Member
variables are related to each other, and they are combined to
provide complete information about an object.
The ,struct keyword is used to define the structure. Let's see the
syntax to define the structure in c.
struct structure_name
{
data_type member1;
data_type member2;
.
.
data_type memeberN;
};
E.G.
struct employee
{ int id;
char name[20];
float salary;
};
Key Points of C Structure
● The structure is declared using the “struct” keyword.
● Structure allocates contiguous memory to all its member variables.
● You can only declare member variables in a structure.
● You cannot initialise the member variables during their declaration.
● To access the member variables, use the dot operator.
● Structure member variables are initialised in the same order as their
declaration.

Example :
#include <stdio.h>
struct book{
char title[50];
char author[30];
double price;
int pages;
};
int main(){
struct book book1 = {"An Era of Darkness", "Shashi Tharoor", 599.00,
360};
printf("Title: %s n", book1.title);
printf("Author: %s n", book1.author);
printf("Price: %.2fn", book1.price);
printf("Pages: %d n", book1.pages);
return 0;
}
Output :
Title: An Era of Darkness
Author: Shashi Tharoor
Price: 599.00
Pages: 360
Keyword typedef :
We use the typedef keyword to create an alias name for data types. It is
commonly used with structures to simplify the syntax of declaring
variables.
Example :
#include <stdio.h>
#include <string.h>
// struct with typedef person
typedef struct Person {
char name[50];
int citNo;
float salary;
} employee;

int main() {
// create struct Person variable with aliased name employee
employee p1;
// assign value to name of p1
strcpy(p1.name, "Gaurav Therade");
// assign values to other p1 variables
p1.citNo = 411001;
p1. salary = 25000;
// print struct variables
printf("Name: %sn", p1.name);
printf("Citizenship No.: %dn", p1.citNo);
printf("Salary: %.2f", p1.salary);
return 0;
}
Output :
Name: Gaurav Therade
Citizenship No.: 411001
Salary: 25000.00
Example :
Taking input from user how many person and take details of all person
and print the details by using loops
#include <stdio.h>
#include <string.h>
typedef struct Person {
char name[50];
int citNo;
float salary;
} employee;
int main() {
int numPersons;

// Input the number of persons
printf("Enter the number of persons: ");
scanf("%d", &numPersons);
// Array of employees based on the number of persons
employee emp[numPersons];
// Input details for each person
for (int i = 1; i <= numPersons; i++) {
printf("Enter details for person %d:n", i);
// Input name
printf("Name: ");
scanf(" %[^n]s", emp[i].name);
// Input city number
printf("City No.: ");
scanf("%d", &emp[i].citNo);
// Input salary
printf("Salary: ");
scanf("%f", &emp[i].salary);
}
// Print details for each person
printf("nDetails of all the Employees :n");
for (int i = 1; i <= numPersons; i++) {
printf("Person %d:n", i);
printf("Name: %sn", emp[i].name);
printf("Citizenship No.: %dn", emp[i].citNo);
printf("Salary: %.2fn", emp[i].salary);
}
return 0;
}

Union in C
structures and unions both serve the purpose of grouping data
members into a single unit, they have different use cases due to
their fundamental differences in memory allocation
structures and unions are similar in that they both allow you to
define custom data types.
Structures are typically used when you want to store and manipulate
different types of data together as a single entity. Each member of a
structure has its own memory space, and you can access them
independently.
Unions are used when you need to store different types of data in the
same memory location. Unlike structures, where each member has its
own memory space, in a union, all members share the same memory
space. This means that modifying one member of a union can affect the
values of other members.
When we Use Structure:
Use structures when you have a collection of related data elements
that you want to access independently and manipulate separately.
When we Use Union:
Use unions when you need to save memory and when you know
that only one member of the union will be accessed at any given time.
Unions are commonly used in situations like implementing variant types
or when dealing with hardware interfaces where memory conservation is
crucial.

Example:
#include <stdio.h>
union student {
int id;
float marks;
char grade;
};
int main() {
union student s;
s.id = 101;
printf("Student ID: %dn", s.id);
s.marks = 85.5;
printf("Student Marks: %fn", s.marks);
s.grade = 'A';
printf("Student Grade: %cn", s.grade);
return 0;
}
Output :
Student ID: 101
Student Marks: 85.500000
Student Grade: A
Difference between Struct & Union:
Features Struct Union
Memory Allocation Each member has their
own memory location
All members share the same memory
location
Size Sum of sizes of all
members
Size of the largest member
Usage Store related data Save memory by sharing memory location
Initialization Members can be initialized
individually
Only the first member can be initialized
Accessing Members Dot (.) operator Dot (.) or arrow (->) operator

Chapter 9 - Pointer
A Variable that stores the memory address of another variable.
Syntax:
int num = 3;
int *ptr = &num;
int num_1 = *ptr;
Note:
* is value of address operator
& is address of operator
num num_1 ptr
34 34 4673
4673 4674 4677
** different ways to declare pointers, pointers also be an int, float and
char.
Format Specifier for pointers:
“%p” or “%u” - unsigned int
Example:
1) Print the address of the operator.
#include<stdio.h>
int main(){
int num = 34;
int *ptr = &num;
printf("%pn",&num);
printf("%pn",ptr);
printf("%pn",&ptr);
return 0;
}

2) Print the Value of Operator.
#include<stdio.h>
int main(){
int num = 34;
int *ptr = &num;
printf("printing the values in diffrent waysn");
printf("%dn",num);
printf("%dn",*ptr);
printf("%dn",*(&num));
return 0;
}
3) Guess the Output of the following code.
#include<stdio.h>
int main(){
int a;
int *ptr;
ptr = &a;
*ptr = 0;
printf("a is: %dn",a);
printf("*ptr is: %dn",*ptr);
*ptr += 5;
(*ptr)++;
return 0;
}

Pointer to pointer:
A variable that stores the memory address of another pointer.
num pptr ptr
34 4677 4673
4673 4676 4677
Syntax:
float marks = 90.00;
float *ptr = &marks;
float **pptr = &ptr;
Example:
#include<stdio.h>
int main(){
float marks = 90.00;
float *ptr = &marks;
float **pptr = &ptr;
printf("%.2fn",**pptr);
return 0;
}
Pointers in Function Call:
1) Call by Value : We pass the value of the variable as an argument.
#include<stdio.h>
void square(int n);
int main(){
int number = 4;
square(number);
printf("number = %dn",number);
return 0;
}
void square(int n){
n = n * n;
printf("square = %dn",n);
}

2) Call By Reference :
We Pass Address of the variable as an argument.
#include<stdio.h>
void square_1(int *n);
int main(){
int number = 4;
square_1(&number);
printf("number = %dn",number);
return 0;
}
void square_1(int* n){
*n = (*n) * (*n);
printf("square = %dn",*n);
}
Questions :
1) Write a C program to swap two numbers using a pointer.
2) Write a C program to calculate and return sum, product and average
by using a function.

Chapter 10 - File I/O
What are files in C?
A file is used to store huge data. C provides multiple file management
functions like file creation, opening and reading files, Writing to the file,
and closing a file. The file is used to store relevant data and file handling
in C is used to manipulate the data.
Operation of Files :
1) Open a File
2) Close File
3) Create a File
4) Read From a File
5) Write in a File
Types of Files :
1) Text Files (textual data) - .txt, .c
2) binary Files (binary data) - .exe,.mp3,.jpg
File Pointer :
For Performing operations on the file in c a special pointer is used called
File pointer that can be declared as: FILE *fptr;
Opening & Closing a File :
#include <stdio.h>
int main(){
FILE *fptr;
fptr = fopen("filename", "mode");
// some work on file
fclose(fptr); //closing file
return 0;
}

File Opening Modes :
1) "r" - Open to read
2) "rb" - Open to read in binary
3) "w" - Open to write
4) "wb" - Open to write in binary
5) "a" - Open to append
Reading from a file :
char c;
fscanf(fptr,"%c",&c);
Example:
#include <stdio.h>
int main(){
FILE *fptr;
fptr = fopen("test.txt", "r");
char ch;
fscanf(fptr,"%c",&ch);
printf("%c",ch);
printf("%c",ch);
printf("%c",ch);
printf("%c",ch);
printf("%c",ch);
fclose(fptr);
return 0;
}
Writing to a file :
char ch = 'H';
fprintf(fptr,"%c",ch);

Example:
#include <stdio.h>
int main(){
FILE *fptr;
fptr = fopen("test.txt", "w");
fprintf(fptr,"%c", 'H');
fprintf(fptr,"%c", 'e');
fprintf(fptr,"%c", 'y');
fprintf(fptr,"%c", '!');
fclose(fptr);
return 0;
}
Writing to a file :
fgetc(fptr);
fputc('A',fptr);
Example:
1) Read from the file
#include <stdio.h>
int main(){
FILE *fptr;
printf("%cn",fgetc(fptr));
fclose(fptr);
return 0;
}

2) write into a file
#include <stdio.h>
int main(){
FILE *fptr;
fptr = fopen("test.txt", "w");
fputc('A',fptr);
fputc('K',fptr);
fputc('A',fptr);
fputc('A',fptr);
fputc('Y',fptr);
fclose(fptr);
return 0;
}
EOF (End Of File) : fgetc returns EOF to show that the file has ended
#include <stdio.h>
int main(){
FILE *fptr;
char ch;
ch = fgetc(fptr);
while(ch != EOF){
printf("%c",ch);
ch = fgetc(fptr);
}
fclose(fptr);
return 0;
}
Questions :
1) Make a program to input student information from user & enter into file
2) wap to write all the odd numbers from 1 to 100 in a file
3) Write a multiplication table of the user entered number in the file.
4) take student number and subjects of each student & calculate their sum
and average store them into the file.

Chapter 11 - Dynamic Memory Allocation in c
Dynamic memory allocation is a way to allocate memory to a data structure
during the runtime.
Following function are available in C to perform Dynamic memory Allocation:
1) malloc()
2) Calloc()
3) free()
4) realloc()
malloc() function:
Malloc stands for memory allocation. It takes a number of bytes to be
allocated as an input and returns a pointer of type void.
Syntax:
#include<stdio.h>
#include<stdlib.h>
int main(){
int *ptr;
ptr = (int *)malloc(5* sizeof(int));
ptr[0] = 1;
ptr[1] = 2;
ptr[2] = 3;
ptr[3] = 4;
ptr[4] = 5;
for(int i =0;i<5;i++){
printf("n %d",ptr[i]);
}
return 0;
}

calloc() function:
Calloc stands for continuous allocation. It initialises each memory block
with a default value of 0.
Syntax:
#include<stdio.h>
#include<stdlib.h>
int main(){
int *ptr;
ptr = (int *)calloc(5, sizeof(int));
}
return 0;
}
Note: If the space is not sufficient in the device, memory allocation fails and
a NULL pointer is returned.
free() function:
We use the free() function to deallocate the memory or use it to free
memory that is allocated by using malloc & calloc.
Syntax:
#include<stdio.h>
#include<stdlib.h>
int main(){
int *ptr;
int n;
printf("enter the n: ");
scanf("%d",&n);
ptr = (int *)calloc(n, sizeof(int));
free(ptr);

}
return 0;
}
realloc() function:
Realloc is used to increase or decrease memory size using the same
pointer & size. E.g. ptr = realloc(ptr, newSize);
Syntax:
int *ptr;
ptr = realloc(ptr, 8);
Example: allocate memory for 5 numbers then increase it to 8 numbers.
#include<stdio.h>
#include<stdlib.h>
int main(){
int *ptr;
printf("Enter number 5: ");
for(int i = 1; i <= 5; i++){
scanf("%d",&ptr[i]);
}
ptr = realloc(ptr, 8);
printf("Enter number 8: ");
for(int i = 0; i < 8; i++){
scanf("%d",&ptr[i]);
}
//print
for(int i = 1; i <= 8; i++){
printf("number %d is %dn",i,ptr[i]);
}
return 0;
}

Questions :
1) WAP to allocate memory of size n, where n is entered by the user.
2) Create an array of size 5 & enter its values from the user.
3) Allocate memory to store the first 5 odd numbers, then reallocate it to
store the first 6 even numbers.

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