C Exercises: Check whether a number can be express as sum of two prime numbers

C For Loop: Exercise-56 with Solution

Write a program in C to check whether a number can be expressed as the sum of two prime.

Visual Presentation:

Sample Solution:

C Code:

#include <stdio.h>   // Include the standard input/output header file. 
#include <stdlib.h>
#include <math.h>   // Include the math header file. 
int main()
{
    // Variable declarations
int num, i, j, temp1, temp2, ctr=0;
    // Prompting user for input
printf("input the number:\n");
    // Getting user input
scanf("%d", &num);
    // Loop to find pairs of numbers that add up to 'num'
for(i = 2; i<= num/2; i++){
        temp1 = i;
        temp2 = num - i;
        // Checking if 'i' is a prime number
for(j = 2; j <= i/2; j++){
if(i % j == 0){
ctr++;
break;
            }
        }
        // If 'i' is a prime number, check if 'num - i' is also prime
if(ctr == 0){
for(j = 2; j <= (num - i)/2; j++){
if((num - i) % j == 0){
ctr++;
break;
                }
            }
             // If both 'i' and 'num - i' are prime, print the pair
if(ctr == 0)
printf("%d can be written as %d + %d.\n ", num, i, num - i);
        }
                // Resetting the counter
ctr = 0;
    }
return 0;
}

Sample Output:

input the number: 16
16 can be written as 3 + 13.
 16 can be written as 5 + 11.

Flowchart:

C Programming Code Editor:

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