Arrays in c programing. practicals and .ppt

Principles of Programming
Lecture 6: Arrays
 In this chapter, you will learn about
 Introduction to Array
 Array declaration
 Array initialization
 Assigning values to array elements
 Reading values from array elements
 Relationship with pointers
 Passing array to function
 2 Dimensional arrays
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NI S1 2009/10

Introduction to Array
 In C, a group of items of the same type can be set up
using Array
 An array is a group of consecutive memory locations
related by the fact that they all have the same name
and the same type.
 The compiler must reserve storage (space) for each
element/item of a declared array.
 The size of an array is static (fixed) throughout
program execution.
 To refer to a particular location or element in the
array, we specify the name of the array and its index
(the position number of the particular element in the
array).
2

3
-10
99
-8
100
27
10
1976
-2020
1
Let say we have an array called a.
a[0]
a[1]
a[2]
a[3]
a[4]
a[5]
a[6]
a[7]
a[8]
Name of the array
The position number within
the square brackets is formally
called a subscript. A subscript
can be an integer or an integer
expression. For example if
x = 1 and y = 2, then a[x+y]
is equal to a[3].
Notice that the position
starts from 0.

Array Declaration
 Array declaration is made by specifying the data type,
it’s name and the number of space (size) so that the
computer may reserve the appropriate amount of
memory.
 General syntax:
data_type array_name[size];
 Examples:
 int my_array[100];
 char name[20];
 double bigval[5*200];
 int a[27], b[10], c[76];
4

Array Initialization
 There are 2 ways to initialize an array: during compilation
and during execution.
 During compilation:
 int arr[ ] = {1, 2, 3, 4, 5};
 Unsized array : We can define how many elements that we
want since the array size is not given.
 int arr[3] = {90, 21, 22};
 We can define only 3 elements since the array size is already
given.
 int arr[5] = {2,4};
 Initialize the first two elements to the value of 2 and 4
respectively, while the other elements are initialized to zero.
 int arr[5] = {0};
 Initialize all array elements to zero.
5

Array Initialization cont…
 During execution:
 Using loop to initialize all elements to zero
int arr[3], index;
for (index = 0; index < 3; index++)
arr[index] = 0;
 Using loop and asking the user to specify the value
for each element.
int arr[3], index;
{
printf (“Enter number:n”);
scanf(“%d”,&arr[index]);
}
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Assigning value to array element
 We can assign a value to a specific array element by using
its index number.
 Example: let’s say we have an array that represent the
number of inhabitant in 5 unit apartments.
int apartment[5]={3,2,6,4,5};
 The above initialization indicates that there are 3 people
living in apartment 0, 2 people living in apartment 1 and
so on.
 Let say that we have a new born in apartment 3, so we
need to change the number of inhabitant living in
apartment three.
apartment[3] = apartment[3] + 1;
 Now, we have the following values in our array:
7
3 2 6 5 5
[0] [1] [2] [3] [4]
apartment

Reading values from array elements
 We can read a value from a specific array element by referring to
the index.
 For example, let’s say we want to know how many people leaving
in apartment 3, we could simple do this:
int apartment[5] = {3,2,6,4,5};
int no_of_people;
no_of_people = apartment[3];
printf(“Apartment 3 has %d people”,no_of_people);
 The above C code will produce the following output:
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Hint!!! Remember that array’s index starts at 0
Apartment 3 has 4 people
Press any key to continue

Example 1: finding total inhabitants
#include <stdio.h>
#define size 5
int main(void)
{
int apartment[size] = {3,2,6,4,5};
int index, total = 0;
for (index = 0; index < size; index++)
{
total = total + apartment[index];
}
printf("There are total of %d inhabitants",total);
return(0);
}
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There are total of 20 inhabitants

Example 2: list down number of inhabitants in each apartment
#include <stdio.h>
int main(void)
{
int apartment[5] = {3,2,6,4,5};
int index, total = 0;
printf("%-7s %-15sn","Apt No", "No of people");
{
printf("%4d %10dn",index,
apartment[index]);
}
return(0);
}
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Apt No No of people
0 3
1 2
2 6
3 4
4 5

Passing Array to a Function
 When we pass an array to a function, we are actually
passing the reference (address) of the first element in
the array to the function. Therefore, any changes to
the array inside the function will also change the
actual array inside the calling function.
 When we want to pass an array to a function, we
need to know these 3 things.
 How to write the function prototype?
 How to do function call?
 How does the function header would look like?
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Passing Array to a Function
 Assume that we have the following array declaration.
float marks[10] = {0.0};
 Say for example we want to write a function, called get_marks, which will
read marks from the user and store the marks inside the array.
 Function prototype:
/* data type with square bracket */
void get_marks(float [ ]);
 Function call:
get_marks(marks); /* just pass the array name */
 Function header:
void get_marks(float marks[ ])
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Example: passing array to a function
13
#include <stdio.h>
#define size
void get_marks(float [ ]);
float calc_average(float [ ]);
int main(void)
{
float marks[size] = {0.0}; /*initializing the array
get_marks(marks); /* function call */
printf(“Average for marks given is %.2f”, calc_average(marks));
return(0);
}
void get_marks(float marks[ ]) /* reading the marks from the users */
{
int i;
for (i = 0; i < size; i++)
{
printf("Marks for student %d:",i + 1);
scanf("%f",&marks[i]);
}
}
float calc_average(float marks[ ])
{
float total = 0.0;
int i;
for (i = 0; i < size; i++)
{
total = total + marks[i];
}
return (total / size);
}
Marks for student 1: 56
Average for marks given is 66.2
Example: Passing Array to a Function

2-Dimensional Array
 It is possible to create an array which has more than
one dimension.
 For example:
 2D array: int array[4][2];
 3D array: int array[4][2][10];
 Graphical representation of a 2D array:
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int myarray[4][2] = {1,2,3,4,5,6,7,8};
1 2
3 4
5 6
7 8
This array has 4 rows and 2 columns.
Col 1 Col2
Row 1
Row 2
Row 3
Row 4

2-Dimensional Array cont…
 Variable initialization can also be done this way:
int myarray[4][2] = {{1,2},{3,4},{5,6},{7,8}};
 This method is less confusing since we can see the rows and columns division
more clearly.
 To initialize a 2D array during execution, we need to use a nested for loop:
int row, column
for (row = 0; row < 4; row++)
{
for (column = 0; column < 2; column++)
{
myarray[row][column] = row+column;
}
}
 Although it is possible to create a multi-dimensional array, arrays above 2-
dimensions are rarely used.
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Passing a 2D array to a function
 When a 2D (or higher dimensional) array is passed to
a function, the size of the second (or subsequent)
subscript needs to be specified.
 For example, if we have:
int twoD[4][5];
 Then the function header which would take twoD as an
argument should be declared like this:
void Process2D(int twoD[ ][5])
 An array is stored consecutively in memory regardless
of the number of dimensions. Therefore, specifying
the subscripts in the function parameter will help the
compiler to know the boundary of the different
dimensions.
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Summary
 In this chapter, we have looked at:
 Array declaration and initialization
 Reading and writing from/to array
elements
 Passing array to function
 2 dimensional array
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Exercise
Assume the following array declaration
float number[5] = {2.3, 4.2, 5.0, 7.9, 6.2};
What will be the output of the following statement?
a)printf(“%f”, number[2+2] );
b)printf(“%f”, number[2]+2 );
c)printf(“%f”, number[1*2] );
d)printf(“%f”, number[1]*2 );
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Exercise
int result[5] = {56, 69, 89};
int i = 2;
What will be the output of the following statement?
a)printf(“%d”, result[1]);
b)printf(“%d”, result[4]);
c)printf(“%d”, result[0] + result[1]);
d)printf(“%d %d”, i, result[i]);
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Exercise
int result[3*2];
a) Write C statements that would read the values for the array
element from the user.
b) Write C statements that would list down all the values in
the array.
c) Write C statements that would sum up all the values in the
array.
Rewrite the above task as separate function!!
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