c - 我在这个循环中做错了什么？

Question

#include<stdio.h>
int main()
{
       for ( int i = printf("\nFor loop initialized ") , printf("Intialized value of i is %i", i) ;
            i >= printf("\nCondition checked") , printf("Current value of i is") ;
            printf("\nValue of i is decremented") , i-- )
       {
             printf(" %i", i);
       }

    printf("\nCondition false, Loop exited.");
       return 0;
}

以下是 gcc -Wall -std=c11 -pedantic-errors 给出的错误:

5:53: error: expected declaration specifiers or '...' before string constant
5:84: error: expected declaration specifiers or '...' before 'i'
5:88: warning: value computed is not used [-Wunused-value]

什么是 ... ？

根据我的说法，输出应该是:

For loop initialized Intialized value of i is 21  
Condition checked Current value of i is 21  
Value of i is decremented  
Condition checked Current value of i is 20  
Value of i is decremented  
Condition checked Current value of i is 19  
Value of i is decremented  
Condition checked Current value of i is 18  
Value of i is decremented  
Condition checked  
Condition false, Loop exited.

Answer 1

好的，这是这里发生的事情:

1. 您使用的 C 版本不允许在 for 循环内进行声明。

2. C99 确实允许此类声明，但在 C99 中，i 初始化后的 printf 会导致语法错误，因为它不是另一个声明。

3. 循环无限的原因是因为比较后的逗号运算符，导致循环继续表达式的值是比较后面的printf的结果，即始终非零。