&&運算子，如果它左邊為1，則右邊需要計算；如果左邊為0.則右邊無需計算。 

#include <stdio.h>

int main()
{
    int a, x;
    for (a = 0, x = 0; a <= 1 && !x++;)
    {
        a++;
    }
    printf("a=%d\n", a);
    printf("x=%d\n", x);

	int aa, xx;
    for (aa = 0, xx = 0; aa <= 1 && !xx++; aa++)
    {
        aa++;
    }
    printf("aa=%d\n", aa);
    printf("xx=%d\n", xx);
    return 0;
}