Question

When I run this code gcc gives me the output 10.

Can someone explain to me why it gives me 10? 🙂

#include <stdio.h>

int f(int x) {
    int y;
    y = 2*x;
}

int g() {
    int z;
    return z;
}

int main() {
    int x=5;
    f(x);
    printf("%d\n",g());
}

Answer 1

Here:

int g() {
    int z;
    return z;
}

This reads:

int g():
    reserve memory for an integer, call it z.
    return whatever is in that reserved memory.

You never used that reserved memory for your integer. Its value is whatever was at that address before you chose to use it (or not use it, rather). That value could be anything.

You do the same in your other function. What you are doing is reading uninitialized memory. You can google that up for further information. See also the “stack” and the “heap”, dynamic memory, and other related topics.