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

Tutorial by:Manisha Dubey      Date: 2016-06-17 03:49:59

Example to check if an integer (entered by the user) can be expressed as the sum of two prime numbers of all possible combinations by making a function.

To accomplish this task, `checkPrime()` function is created.

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

## Example: Integer as a Sum of Two Prime Numbers

``````#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 can't be expressed as the sum of two prime numbers.", n);
return 0;
}

// Function to check prime number
int checkPrime(int n)
{
int i, flag = 1;

for(i=2; i<=n/2; ++i)
{
if(n%i==0)
flag=0;
}

return flag;
}``````

Output

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

## C

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