What is the difference between the following 2 C codes?

#include stdio.h //Program 1
    int main()
    {
        int d, a = 1, b = 2;
        d =  a++ + ++b;
        printf("%d %d %d", d, a, b);
    }

#include stdio.h //Program 2
    int main()
    {
        int d, a = 1, b = 2;
        d =  a++ +++b;
        printf("%d %d %d", d, a, b);
    }