C program to find sum of prime numbers between 1 to n

Write a C program to find sum of all prime numbers between 1 to n using for loop. C program to generate sum of all primes between a given range. Logic to find sum of prime numbers in a given range.

Input upper limit: 10

Sum of prime numbers between 1-10: 17

Required knowledge

Basic C programming, If else, For loop, Nested loops

What is Prime number?

Prime numbers are the positive integers greater than 1 that has only two divisors 1 and the number itself. For example: 2, 3, 5, 7, 11 are the first 5 prime numbers.

Logic to find sum of prime numbers between 1 to n

Finding sum of prime number is just a 7 std kid task, if you know checking prime numbers. Before I get to the formal logic of the program. I recommend you to learn the below two concepts before moving on.

• Program to check prime numbers.
• Program to print prime numbers between 1 to n.

Below is the step by step descriptive logic to find sum of prime numbers between 1 to n.

1. Read upper limit to find sum of prime from user. Store it in some variable say n.
2. Initialize another variable sum = 0 to store sum of prime numbers.
3. Run a loop from 2 to n, incrementing 1 in each loop counter. The loop structure should look like for(i=2; i<=n; i++).
4. Inside this loop check if i is prime. Then increment the sum variable by 1 i.e. sum = sum + 1.
5. Finally after loop print the resultant value of sum.

Program to find sum of prime numbers between 1 to n

/**
 * C program to find sum of prime numbers between 1 to n
 */

#include <stdio.h>

int main()
{
    int i, j, n, isPrime, sum=0;

    /*
     * Read upper limit from user
     */
    printf("Find sum of all prime between 1 to : ");
    scanf("%d", &n);

    /*
     * Find all prime numbers between 1 to n
     */
    for(i=2; i<=n; i++)
    {

        /*
         * Check if the current number i is Prime or not
         */
        isPrime = 1;
        for(j=2; j<=i/2 ;j++)
        {
            if(i%j==0)
            {
                isPrime = 0;
                break;
            }
        }

        /*
         * If i is Prime then add to sum
         */
        if(isPrime==1)
        {
            sum += i;
        }
    }

    printf("Sum of all prime numbers between 1 to %d = %d", n, sum);

    return 0;
} 

Program to find sum of prime numbers in given range

/**
 * C program to find sum of prime numbers in given range
 */

#include <stdio.h>

int main()
{
    int i, j, start, end;
    int isPrime, sum=0;

    /*
     * Read lower and upper limit from user
     */
    printf("Enter lower limit: ");
    scanf("%d", &start);
    printf("Enter upper limit: ");
    scanf("%d", &end);

    /*
     * Find all prime numbers in given range
     */
    for(i=start; i<=end; i++)
    {

        /*
         * Check if the current number i is Prime or not
         */
        isPrime = 1;
        for(j=2; j<=i/2 ;j++)
        {
            if(i%j==0)
            {
                isPrime = 0;
                break;
            }
        }

        /*
         * If i is Prime then add to sum
         */
        if(isPrime==1)
        {
            sum += i;
        }
    }

    printf("Sum of all prime numbers between %d to %d = %d", start, end, sum);

    return 0;
} 

Enter lower limit: 10
Enter upper limit: 20
Sum of all prime numbers between 10 to 20 = 60

Happy coding ;)