Calculate the Sum of Natural Numbers in C

Exercise:

Write a C program to calculate the sum of natural numbers.

1. Calculate using for loop

Click Here to View the Solution!
#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;
    }
    printf("Sum = %d", sum);
    return 0;
}
Click Here to View the Output!
Enter a positive integer: 5
Sum = 15
Click Here to View the Explanation!
  • This program is used to calculate the sum of natural numbers using a for loop.
  • The program requests the user to enter a positive number and stores it in an integer variable n using the scanf() function.
  • A for loop is initialized that calculates the sum of the natural numbers by adding a number one at a time in each iteration which continues till the number n is reached in the loop. And each time increment the number by one.
  • The result of additions is stored in a variable sum which is then printed.
  • The return 0 statement is used to exit the program execution.

2.Calculate using while loop

Click Here to View the Solution!
#include <stdio.h>
int main() {
    int n, i=1, sum = 0;
    printf("Enter a positive integer: ");
    scanf("%d", &n);
    while (i <= n) {
        sum += i;
        ++i;
    }
    printf("Sum = %d", sum);
    return 0;
}
Click Here to View the Output!
Enter a positive integer: 68
Sum = 2346
Click Here to View the Explanation!
  • This program is used to calculate the sum of natural numbers using a while loop.
  • The program requests the user to enter a positive number and stores it in an integer variable n using the scanf() function.
  • The while loop states a condition which keeps the loop iterating for n number of times and keeps adding the number i in the variable sum and increments i by one each time.
  • The sum is then printed and displayed on the screen.
  • The for loop is preferred over the while loop since the number of iterations are known in a for loop.
  • The return 0 statement is used to exit the program execution.

3. Read Input Until user enters Positive Integer

Click Here to View the Solution!
#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;
    }
    printf("Sum = %d", sum);
    return 0;
}

Click Here to View the Output!
Enter a positive integer: 6 
Sum = 21
Click Here to View the Explanation!
  • This program is used to calculate the sum of natural numbers using a while loop.
  • The program requests the user to enter a positive number and stores it in an integer variable n using the scanf() function.
  • The while loop states a condition which keeps the loop iterating for n number of times and keeps adding the number i in the variable sum and increments i by one each time.
  • The sum is then printed and displayed on the screen.
  • The for loop is preferred over the while loop since the number of iterations are known in a for loop.
  • The return 0 statement is used to exit the program execution.
  • In order to avoid a negative input, a do…while loop can be used which requests the user to keep entering a number until a positive number is scanned as an input.