PROGRAM-1:
sum of natural numbers using for loop
#include <stdio.h>
int main()
{
int n, i, sum = 0;
printf("Enter a positive integer: ");
scanf("%d",&n);
for(i=1; i <= n; ++i)
{
sum += i; // sum = sum+i;
}
printf("Sum = %d",sum);
return 0;
}
OUTPUT:
Enter a positive integer: 100
Sum = 5050
PROGRAM-2:
Sum of natural numbers using while loop
#include <stdio.h>
int main()
{
int n, i, sum = 0;
printf("Enter a positive integer: ");
scanf("%d",&n);
i = 1;
while ( i <=n )
{
sum += i;
++i;
}
printf("Sum = %d",sum);
return 0;
}
Output
Enter a positive integer: 100
Sum = 5050
PROGRAM-3:
Program to read input until user enters a positive integer
#include <stdio.h>
int main()
{
int n, i, sum = 0;
do {
printf("Enter a positive integer: ");
scanf("%d",&n);
}
while (n <= 0);
for(i=1; i <= n; ++i)
{
sum += i; // sum = sum+i;
}
printf("Sum = %d",sum);
return 0;
}
OUTPUT:
Enter a positive integer: 100
Sum = 5050
