C语言之递归

#include <stdio.h>void e(int);int main(void){   int a = 3;   e(a);   putchar('\n');   return 0;}void e(int n){   if (n > 0)   {      e(--n);      printf("%d ", n);      e(--n);   }}

e(0), e(-1) -> {}
e(1) -> {e(0), print 0, e(-1)} -> {{}, print 0, {}} -> {print 0}
e(2) -> {e(1), print 1, e(0)} -> {{print 0}, print 1, {}} -> {print 0, 1}
e(3) -> {e(2), print 2, e(1)} -> {{print 0, 1}, print 2, {print 0}} -> {print 0, 1, 2, 0}