Lecture 14 – Loops (while)


Sentinel controlled

There’s a problem with for loop. That is, if we want to terminate the program pre-maturely based upon a condition, we cannot do it. It will execute for the specified number of times.

For achieving this functionality, we have two sentinel controlled loops. The term sentinel refers to a guard.

while loop

In while loop the condition is checked first and the control is transferred to the loop’s body.

Syntax

initialization

while(termination_conditon)

{

// Statements to be executed

meansToGetToTerminationCondition

}

 


Figure 3- Breakup of while loop

 

Let’s continue with Example 23, let’s compare both loops

 

With for loop
With while loop
Example 25 - Display name five times using while loop

Output
Hammad Naqvi
Hammad Naqvi
Hammad Naqvi
Hammad Naqvi
Hammad Naqvi
#include <stdio.h>


#include <conio.h>
void main()
{
int count=0;
clrscr();
 
for(count=1; count<=5; count++)
                {
                printf(“\nHammad Naqvi”);
                }
getch();
}             

Output
Hammad Naqvi
Hammad Naqvi
Hammad Naqvi
Hammad Naqvi
Hammad Naqvi
#include <stdio.h>
#include <conio.h>
void main()
{
int count=1;
clrscr();
while(count<=5)
                {
                printf(“\nHammad Naqvi”);
 
                count++;
                }
getch();
}

Table 9 - Comparison of for and while loop


Output
Enter your marks (-ve number to quit): 5
Enter your marks (-ve number to quit): 7
Enter your marks (-ve number to quit): 15
Enter your marks (-ve number to quit): 13
Enter your marks (-ve number to quit): 22
Enter your marks (-ve number to quit): 21
Enter your marks (-ve number to quit): 5
Enter your marks (-ve number to quit): -1
 
Average marks 12.57142
This was same example with two different loop constructs. Now let’s have another example in which I shall show you how you can limit the iteration of the loop based upon condition. Consider a scenario where you have to calculate average marks of the students in computer science subject, and you do not know the number of students at hand. The program would be able to calculate the number of students automatically.

#include <stdio.h>

#include <conio.h>

void main()

{

int student_count=0;

float marks=0.0, total_marks=0.0; average_marks=0.0;

clrscr();

printf(“\nEnter your marks (-ve number to quit):”);

scanf(“%f”, &marks);

student_count=1;

total_marks = total_marks + marks;

while(marks>0)

                {

                printf(“\nEnter your marks (-ve number to quit):”);

scanf(“%f”, &marks);

total_marks = total_marks + marks;

student_count = student_count + 1;                       // or you can write student_count++

                }

average_marks = (total_marks-marks) / (student_count-1);

printf(“\n\nAverage marks %f”, average_marks);

getch();

}

Example 26 - Calculating average marks using while loop

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