C Language Example - Check Whether a Number Can Be Expressed as the Sum of Two Prime Numbers
Check whether a number can be expressed as the sum of two prime numbers.
Example
#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)
{
// Test and determine
if (checkPrime(i) == 1)
{
if (checkPrime(n-i) == 1)
{
printf("%d = %d + %d\n", n, i, n - i);
flag = 1;
}
}
}
if (flag == 0)
printf("%d cannot be decomposed into two prime numbers.", n);
return 0;
}
// Determine whether it is a prime number
int checkPrime(int n)
{
int i, isPrime = 1;
for(i = 2; i <= n/2; ++i)
{
if(n % i == 0)
{
isPrime = 0;
break;
}
}
return isPrime;
}
The output result is:
输入正整数: 34 34 = 3 + 31 34 = 5 + 29 34 = 11 + 23 34 = 17 + 17other extensions