🚀 Programming Example

C Program - Integer as a Sum of Two Prime Numbers

👁 1,189 Views

💻 Practical Program

📘 Step Learning

Integer as a Sum of Two Prime Numbers.

📌 Information & Algorithm

If you don't know what is prime number please read form this tutorial. Prime Number & Prime Factors

💻 Program Code

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

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

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

    for(i = 2; i &lt;= n/2; ++i)
    {
        if(n % i == 0)
        {
            isPrime = 0;
            break;
        }  
    }

    return isPrime;
}

🖥 Program Output

Enter a positive integer: 34
34 = 3 + 31
34 = 5 + 29
34 = 11 + 23
34 = 17 + 17

📘 Explanation

To understand this example, you should have the knowledge of following C programming topics:

C if, if...else and Nested if...else Statement
C Programming for Loop
C Programming Functions
C Programming User-defined functions
To accomplish this task, checkPrime() function is created.

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

🎯 How to learn from this example

First understand the algorithm carefully. Then study the program line-by-line and compare it with the output. Finally, review the explanation section to strengthen your logic and programming understanding.

🔥 Practice suggestion

Rewrite the program without looking at the code. Modify values, conditions or logic and run it again. This helps improve confidence and strengthens coding skills much faster.