c++ - 如何编写一个没有变量的for循环？

Question

我想直接写一个for循环，不带任何变量。可能吗？

示例:

for (1; 1 <= 4; ++) {
  printf ("Loop working\n");
}

预期输出:

Loop working
Loop working
Loop working
Loop working

Answer 1

您需要一个变量来保持计数，但您可以隐藏它。

#include <stdio.h>

#define JOIN(a, b) (a ## b)
// WARNING: don't LOOP in the same line
#define LOOP(n) for (unsigned JOIN(HIDDEN, __LINE__) = 0; JOIN(HIDDEN, __LINE__) < n; JOIN(HIDDEN, __LINE__)++)

int main(void) {
    LOOP(4) {
        printf("foo");
        LOOP(2) printf(" bar");
        puts("");
    }
    return 0;
}

See code running on ideone

输出

foo bar bar
foo bar bar
foo bar bar
foo bar bar