C++ Exercises: Check Whether a Number can be Express as Sum of Two Prime Numbers

C++ For Loop: Exercise-33 with Solution

Write a program in C++ to Check Whether a Number can be Express as Sum of Two Prime Numbers.

Pictorial Presentation:

Sample Solution:-

C++ Code :

#include <iostream>
using namespace std;

int main()
{
    int n, i, flg1 = 1, flg2 = 1, flg3 = 0, j;
    float sum = 0;
    cout << "\n\n Check Whether a Number can be Express as Sum of Two Prime Numbers:\n";
    cout << "------------------------------------------------------------------------\n";
    cout << " Input  a positive integer: ";
    cin >> n;
    for (i = 2; i <= n / 2; i++) 
    {
        /*---------- check for prime---------------*/
        flg1 = 1;
        flg2 = 1;
        for (j = 2; j < i; j++) 
        {
            if (i % j == 0) 
            {
                flg1 = 0;
                j = i;
            }
        }
        for (j = 2; j < n - i; j++) 
        {
            if ((n - i) % j == 0) 
            {
                flg2 = 0;
                j = n - i;
            }
        }
        if (flg1 == 1 && flg2 == 1) 
        {
            cout << n << " = " << i << " + " << n - i << endl;
            flg3 = 1;
        }
    }
    if (flg3 == 0) 
    {
        cout << n << " can not be expressed as sum of two prime numbers." << endl;
    }
}

Sample Output:

 Check Whether a Number can be Express as Sum of Two Prime Numbers:    
------------------------------------------------------------------------                                                                      
 Input  a positive integer: 20                                         
20 = 3 + 17                                                            
20 = 7 + 13   

Flowchart:

C++ Code Editor:

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