prime_numbers_abc_bac_v1.c

/*

    prime_numbers_abc_bac_v1.c

    Task:
    A 3-digit prime number 'ABC' is such that C= A+B and 'BAC' is also prime.
    Find all possible values of 'ABC'.


    You can find all my C programs at Dragan Milicev's pastebin:

    https://pastebin.com/u/dmilicev

*/

#include <stdio.h>

// If the number is prime, function returns that number, otherwise returns 0
int IsPrimeNumber_1(int number)
{
    int i;                          // counter for loop
                                    // i<number !!!
    for(i=2; i<number; i++)         // it is enough to go to the number !
        if(number % i == 0)         // if the number is divisible by i,
            return 0;               // it is not prime number

    return number;                  // number is prime number
}

int main(void)
{
    int a, b, c, abc, bac, solved=0;

    for(a=0; a<10; a++)
        for(b=0; b<10; b++)
            for(c=0; c<10; c++)
            {
                abc = a*100 + b*10 + c;
                bac = b*100 + a*10 + c;

                if( IsPrimeNumber_1(abc) &&
                    IsPrimeNumber_1(bac) &&
                    c == a + b &&
                    a != 0 &&
                    b != 0 )
                {
                    solved = 1;
                    printf("\n a = %d \t b = %d \t c = %d \t %5d \t %5d \n", a, b, c, abc, bac );
                }
            }

    if( !solved )
        printf("\n There is no such digits. \n");

    return 0;

} // main()