Introduction

• Group of statements that are executed repeatedly while some condition remains true
• Each execution of the group of statements is called an iteration of the loop

The while Loop

Example1:Find the sum of digits of a number

void main()
{
int n, sum=0;
scanf ("%d",&n);
while (n != 0) {
sum = sum + (n % 10);
n = n / 10;
}
printf ("The sum of digits of the number is %d \n", sum);
}

Example2:Find the sum of Square of digits of a number

void main() {
int N, count, sum;
scanf ("%d", &N) ;
sum = 0;
count = 1;
while (count <= N)
{
	sum = sum + count * count;
	count = count + 1;
}
printf ("Sum = %d\n", sum) ;
return 0;
}

Example-3

The For Loop

1. Initialization, loop-continuation test, and update can contain arithmetic expressions

   for( k = x; k <= 4 * x * y; k +=y / x )

2. Update may be negative (decrement)

   for (num = 10; num >= 0; --num)

3. If loop continuation test is initially 0 (false):
• body of for structure not performed
No statement executed
• Program proceeds with statement after for structure

Example:Computing Factorial

void main () 
{
int N, count, prod;
scanf ("%d",&N) ;
prod = 1;
for (count = 1;count <= N; ++count)
{
	prod = prod * count;
}
printf ("Factorial = %d\n", prod) ;
}

Nesting of for Loop

void main()
{
int row,i,j,k;
printf("Enter number of row for pattern:");
scanf("%d",&row);
for(i=1;i<=row;++i)
{
	for(j=1;j<=i;j++)
	{
		printf("*");
	}
printf("\n");
}

}

Output:
Enter number of row for pattern:5
*
**
***
****
*****

void main()
{
int row, col,ROWS;
printf("Enter number of row for pattern:");
scanf("%d",&ROWS);
for (row=0; row < ROWS; ++row) {
	for (col=1; col<=row; ++col)
		printf(" ");
	for (col=1; col<=ROWS-row; ++col)
		printf("* ");
printf ("\n");
}
}

Output:
Enter number of row for pattern:10
* * * * * * * * * * 
 * * * * * * * * * 
  * * * * * * * * 
   * * * * * * * 
    * * * * * * 
     * * * * * 
      * * * * 
       * * * 
        * * 
         * 

Equivalance of while and for Loop

The do-while Loop

Example:Decimal to binary conversion(prints binary in reverse order)

void main() {
int dec;
scanf ("%d", &dec);
do
	{
	printf ("%2d", (dec % 2));
	dec = dec / 2;
	} while (dec != 0);
printf ("\n");
}

Echo characters typed on screen until end of line
void main () {
char echo ;
do {
scanf ("%c", &echo);
printf ("%c",echo);
} while (echo != '\n') ;
}

The continue statement

The continue statement in C programming works somewhat like the break statement.
Instead of forcing termination,it forces the next iteration of the loop to take place,skipping any code in between.

For the for loop, continue statement causes the conditional test and increment portions of the loop to execute.
For the while and do...while loops, continue statement causes the program control to pass to the conditional tests.

Syntax
The syntax for a continue statement in C is as follows:
continue;

Example of continue in do-While loop
#include <stdio.h>
int main()
{
   int j=0;
   do
   {
      if (j==7)
      {
         j++;
         continue;
      }
      printf("%d ", j);
      j++;
   }while(j <10);
   return 0;
}

Output:
0 1 2 3 4 5 6 8 9

An Example with break and continue

void main() {
int fact = 1;
int i = 1;
while (1) {
fact = fact * i;
++i;
if ( i <=10 )
continue; 	/* not done yet ! Go to loop and perform next iteration*/
break;
	}

Chapter 5 Quiz