在while循环中使用scanf函数 [英] Using the scanf function in while loop

问题描述

我正在尝试为编程作业格式化以空格分隔的用户输入.

I am attempting to format a space-delimited user input for a programming assignment.

本质上，输入由任意数量的表达式组成

Essentially, the input consists of an arbitrary number of expressions

L integer integer integer 和 C integer integer integer.

例如:L 1 1 5 7 C 4 5 3.

到目前为止，我已经设法根据初始字符提取整数，并且可以使用 scanf 函数遍历字符串:

So far, I've managed to extract the integers depending on the initial character, and can iterate through the string using the scanf function:

char a;
while(scanf("%c", &a) == 1){
    if(a == 'C'){
        int inputX, inputY, inputR;
        scanf("%d %d %d", &inputX, &inputY, &inputR);
        printf("%d %d %d
", inputX, inputY, inputR);
    }
    else if(a == 'L'){
        int x1, y1, x2, y2;
        scanf("%d %d %d %d", &x1, &y1, &x2, &y2);
        printf("%d %d %d %d
", x1, y1, x2, y2);
    }
}

不幸的是，虽然这会输出所需的整数，但循环(和用户输入提示)并没有终止.

Unfortunately, although this outputs the desired integers, the loop (and user input prompt) doesn't terminate.

有人能告诉我为什么会这样吗?

Could someone please enlighten me as to why this is happening?

推荐答案

这是因为 总是在那里使 scanf("%c", &a) ==1 总是正确的.
改变你的

This is because is always there to make scanf("%c", &a) == 1 always true.
Change your

while(scanf("%c", &a) == 1) 

到

while(scanf(" %c", &a) == 1)  
     //      ^space before format specifier.  

%c 之前的空格会吃掉 scanf 留下的这个 (按 Enter).

A space before %c will eat up this left behind by scanf (on pressing Enter).

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