Constructs (Programming Methodology)

CONSTRUCTS
(IMPERATIVE PROGRAMMING
LANGUAGE)
Selection Constructs
Conditional Constructs
Looping Constructs
By: Jyoti Bhardwaj
Roll no: 04
F.Y. M.C.A

SELECTION CONSTRUCTS.
THE SELECTION CONSTRUCT:
The selection construct allows you to create a program that will select one of a
number of different alternative courses of action. It is also called the if..then..else
construct.
 A selection statement provides for selection between alternatives. We can identify two
types of selection constructs:
 If statements
 Case statements
IF STATEMENT:
 An if statement, sometimes referred to as a conditional, can be used in two forms:
 If condition then action1
if (condition1) action1;
if (condition2) action2;
.
.
.
if (conditionN) actionN;
 If condition then action1 else action2

if... else example
main()
{
int i;
printf("nEnter a number : ");
scanf("%d",&i);
if( i > 7 )
printf("I is greater than seven");
else
printf("I is not greater than seven");
}
Output:
Enter a number: 5
I is not greater than seven

CASE STATEMENT:
 Switch case statements are a substitute for long if statements that
compare a variable to several values. Case statements allow selection
from many alternatives.
 The switch expression is evaluated once.
 The value of the expression is compared with the values of each case.
 If there is a match, the associated block of code is executed.
Using break keyword:
 If a condition is met in switch case then execution continues on into
the next case clause also if it is not explicitly specified that the
execution should exit the switch statement.This is achieved by
using break keyword.
What is default condition:
 If none of the listed conditions is met then default condition
executed.

The basic format for using switch case is outlined below:
switch(expression)
{
case 1:
code block
break;
case 2:
code block
break;
.
.
case n:
code block
break;
default:
default code block
}

Selection structure vary from language to language,
but they tend to agree on the following:
 Case Selection can appear in any order.
 Case Selections do not have to be consecutive, meaning that it is
valid to have case-1, and case-4 without case-2 and case-3.
 Case Selection must have distinct actions for each case,
otherwise we need to combine the actions to avoid conflict.
To Sum up, the effect of Switch structure is as follows:
 Evaluate the switch expression.
 Go to the case label having a constant value that matches the
value of the expression found in step 1; If a match is found, go
to the default label; if there is no default label; terminate the
switch.
 Terminate the switch when break statement in encountered.

Switch… case example:
main()
{
int Grade = 'B';
switch(Grade )
{
case 'A' : printf( "Excellentn" );
break;
case 'B' : printf( “Very Goodn" );
break;
case 'C' : printf( "Good n" );
break;
case 'D' : printf( “O.K. n" );
break;
case 'F' : printf( “Satisfactory n" );
break;
default : printf( “Fair n" );
break;
}
}
This will produce following result:
Good

CONDITIONALCONSTRUCTS.
 The conditional construct allows you to create a program that
will select one of a number of different alternative courses of
action. It is also called the if..then..else construct.
 The initial if statement checks a condition (in this case >= 50).
If the condition is true, then the series of commands following
it are executed. If the condition is false (i.e. the user enters a
mark less than 50), then the series of commands following the
else statement are executed.
Note:
 An if statement must check a condition and then be followed
by the word then.
 An if statement must have an end if to finish it off.
 An if statement does not have to have an else statement.

If…else Ladder:
if (expression)
{
Block of statements;
}
else
{
Block of statements;
}
if (expression)
{
Block of
statements;
}
else if(expression)
{
Block of
statements;
}
else
{
Block of
statements;
}

if... else example
int main()
{
int year;
printf("Enter a year: ");
scanf("%d",&year);
if(year%4 == 0)
{
if( year%100 == 0)
{
if ( year%400 == 0)
printf("%d is a leap year.", year);
else
printf("%d is not a leap year.", year);
}
else
printf("%d is a leap year.", year );
}
else
printf("%d is not a leap year.", year);
return 0;
}

LOOPINGCONSTRUCTS:
The loop constructs is
used to execute a block
of code until the
condition becomes
expired.
Loop constructs saves
the programmer from
writing code multiple
times that has
repetitive in nature

Types of loop to handle looping requirements
LoopType Description
 while loop Repeats a statement or group of
statements while a given condition
is true. It tests the condition before
executing the loop body.
 for loop Execute a sequence of statements
multiple times.
 do...while loop Like a while statement, except that it
tests the condition at the end of the
loop body
 nested loops You can use one or more loop inside
any another while, for or do..while
loop.

The Infinite Loop:
 A loop becomes infinite loop if a condition never
becomes false.The for loop is traditionally used for this
purpose. Since none of the three expressions that form
the for loop are required, you can make an endless
loop by leaving the conditional expression empty.
 int main ()
{
for( ; ; )
{
printf("This loop will run forever.n");
}
return 0;
}

While loop example..
 In while loop control statement, loop is executed until condition becomes false.
 Syntax:
while( condition )
body;
 int main()
{
int i=3;
while(i<10)
{
printf("%dn",i); i++;
}
}
Output:
3 4 5 6 7 8 9

do...while loop examples
 In do..while loop control statement, while loop is executed irrespective of
the condition for first time. Then 2nd time onwards, loop is executed until
condition becomes false.
 int main()
{
int i=1;
do
{
printf("Value of i is %dn",i);
i++;
}
while(i<=4 && i>=2);
}
Output:
Value of i is 1
Value of i is 2
Value of i is 3
Value of i is 4

For loop example.
In for loop control statement, loop is executed until condition becomes false.
 int main()
{
int i;
for(i=0;i<10;i++)
{
printf("%d ",i);
}
}
Output:
0 1 2 3 4 5 6 7 8 9

WhentoUseWhichLoop?
Ifyouknow(orcancalculate)
howmanyiterationsyouneed,
thenuseacounter-controlled(for
)loop.
Otherwise,ifitisimportantthat
theloopcompleteatleastonce
beforecheckingforthestopping
condition,
orifitisnotpossibleor
meaningfultocheckthestopping
conditionbeforetheloophas
executedatleastonce,
thenuseado-whileloop.
Otherwiseuseawhileloop.

Constructs (Programming Methodology)

Constructs (Programming Methodology)

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