C Program: Calculate sum of Prime numbers with Do-While Loop

Last update on July 30 2025 12:56:36 (UTC/GMT +8 hours)

9. Sum of Prime Numbers

Write a C program that calculates and prints the sum of prime numbers up to a specified limit (e.g., 50) using a do-while loop.

Sample Solution:

C Code:

#include <stdio.h>

int isPrime(int num) {
    if (num < 2) {
        return 0;  // Not a prime number
    }
    for (int i = 2; i * i <= num; i++) {
        if (num % i == 0) {
            return 0;  // Not a prime number
        }
    }
    return 1;  // Prime number
}

int main() {
    int limit;
    int num = 2;  // Starting from the first prime number
    int sum = 0;

    // Prompt the user to enter a limit
    printf("Input the limit for prime numbers: ");
    scanf("%d", &limit);

    // Calculate and print the sum of prime numbers up to the specified limit
    do {
        if (isPrime(num)) {
            sum += num;  // Add prime numbers to the sum
        }
        num++;  // Move to the next number
    } while (num <= limit);

    // Print the sum of prime numbers
    printf("Sum of prime numbers up to %d: %d\n", limit, sum);

    return 0;  // Indicate successful program execution
}

Sample Output:

Input the limit for prime numbers: 50
Sum of prime numbers up to 50: 328

Input the limit for prime numbers: 7
Sum of prime numbers up to 7: 17

Explanation:

Here are key parts of the above code step by step:

int isPrime(int num): Function to check if a number is prime. Returns 1 for prime numbers, 0 otherwise.
int limit;: Variable to store the user-specified limit.
int num = 2;: Initializes the variable to start checking prime numbers from 2.
int sum = 0;: Initializes the variable to store the sum of prime numbers.
printf("Enter the limit for prime numbers: ");: Prompts the user to enter the limit.
scanf("%d", &limit);: Reads the user-specified limit.
do { ... } while (num <= limit);: Do-while loop to calculate the sum of prime numbers up to the specified limit.
if (isPrime(num)) { sum += num; }: If the current number is prime, add it to the sum.
num++;: Move to the next number.
} while (num <= limit);: Continue the loop until the specified limit is reached.
printf("Sum of prime numbers up to %d: %d\n", limit, sum);: Print the sum of prime numbers.
return 0;: Indicates successful program execution.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to compute the sum of prime numbers up to a given limit and display the count of prime numbers found.
Write a C program to print only prime numbers up to a given limit while skipping any prime number that ends in 3.
Write a C program to find the sum of prime numbers up to a given limit and display the largest prime number found.
Write a C program to compute the sum of all twin prime numbers up to a specified limit.

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