Functions - General Questions

What happens when a recursive function has no base case?

What will be the output of the program?

#include <stdio.h>
void swap(int *a, int *b) { int t = *a; *a = *b; *b = t; }
int main(void) {
    int x = 1, y = 2;
    swap(&x, &y);
    printf("%d %d\n", x, y);
    return 0;
}