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Check Whether a Number can be Expressed as Sum of Two Prime Numbers



Check Whether a Number can be Expressed as Sum of Two Prime Numbers

To accomplish this task, checkPrime() function is created.

The checkPrime() returns 1 if the number passed to the function is a prime number. 

#include <stdio.h>
int checkPrime(int n);
int main()
{
    int n, j, flag = 0;

    printf("Enter a positive integer: ");
    scanf("%d", &n);

    for(j = 2; j <= n/2; ++j)
    {
        // condition for j to be a prime number
        if (checkPrime(j) == 1)
        {
            // condition for n-j to be a prime number
            if (checkPrime(n-j) == 1)
            {
                // n = primeNumber1 + primeNumber2
                printf("%d = %d + %d\n", n, j, n - j);
                flag = 1;
            }

        }
    }

    if (flag == 0)
        printf("%d cannot be expressed as the sum of two prime numbers.", n);

    return 0;
}

// Function to check prime number
int checkPrime(int n)
{
    int j, isPrime = 1;

    for(j = 2; j <= n/2; ++j)
    {
        if(n % j == 0)
        {
            isPrime = 0;
            break;
        }  
    }

    return isPrime;
}

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