if inside a while loop causing trouble

I'm having trouble on the last part of my program. The code substracts an array p[j] with an input number nStevilo and then puts in into absolute. It then compares the result with a substraction of an array p[j++]. The code should go through the array and find the smallest value and append it into najblizjeStevilo, but for some reason it doesn't work?

while (j < 20){
        if (abs(p[j] - nStevilo) < abs(p[j++] - nStevilo)){
            najblizjeStevilo = p[j];
        }
    }

The array includes 20 prime numbers, starting from 2 (2, 3, 5, 7, 11...), so p[0] = 2, p[1] = 3...