Question

Consider following code:

int main()
{
char c;
for(;(c=getchar())+1;)
    printf("%c\n",c);
}

It gets characters what I enter in terminal and prints them. When I remove +1 in condition, program works but it doesnt stop when EOF (Ctrl+D) signal. When I change it to +2 same problem.

My question is how that +1 work? Is it something related to getchar() or for loop?

Answer 1

That is because the int value of EOF is -1, so what you're doing is loop until the expression(c=getchar())+1) gets the value 0 which is when you read EOF (where value of exrpession is: -1+1=0). Also as wll pointed out in the comments you should declare c as int since getchar() returns int.

Answer 2

for statement works with limits known already if you want a conditional loop use while :

int main()
{
int c;
while ((c=getchar()) != eof())
    printf("%c\n",c);
}

Answer 3

仅适用于+1的原因。
原型：int getchar（void）;

返回值

成功时，返回字符读取（提升为int值）。
返回类型为int以容纳特殊值EOF，表示失败（-1）。
如果标准输入位于文件末尾，则该函数返回EOF并设置标准输出的eof指示符（feof）。
如果发生其他一些读取错误，该函数也会返回EOF，但会设置其错误指示符（ferror）。

getchar() in a for loop condition

3 个答案: