C++ Programming Code Examples
C++ > Mathematics Code Examples
Check Whether a Number can be Express as Sum of Two Prime Numbers in C++
/* Check Whether a Number can be Express as Sum of Two Prime Numbers in C++
Example to check if an integer (entered by the user) can be expressed as the sum of two prime numbers of all possible combinations with the use of functions.
This program takes a positive integer from user and checks whether that number can be expressed as the sum of two prime numbers.
If the number can be expressed as sum of two prime numbers, the output shows the combination of the prime numbers.
To perform this task, a user-defined function is created to check prime number. */
#include <iostream>
using namespace std;
bool checkPrime(int n);
int main()
{
int n, i;
bool flag = false;
cout << "Enter a positive integer: ";
cin >> n;
for(i = 2; i <= n/2; ++i)
{
if (checkPrime(i))
{
if (checkPrime(n - i))
{
cout << n << " = " << i << " + " << n-i << endl;
flag = true;
}
}
}
if (!flag)
cout << n << " can't be expressed as sum of two prime numbers.";
return 0;
}
// Check prime number
bool checkPrime(int n)
{
int i;
bool isPrime = true;
for(i = 2; i <= n/2; ++i)
{
if(n % i == 0)
{
isPrime = false;
break;
}
}
return isPrime;
}
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Internal method to test if a positive number is prime. Not an efficient algorithm and Internal method to return a 'prime number' at least as large as n. Assumes "n > 0". Insert item x into
