c - 请解释一下这个...我被困住了

Question

我已经开始做 C 语言，最近我开始做 Dennis Ritchie 和 Brian Kernighan 写的 C 编程书......我坚持练习 1.9“编写一个 C 程序以将其输入复制到它的输出，将一个或多个空格的每个字符串替换为一个空格”...我尝试了很多方法...查看互联网并找到了答案，但没有解释...我见过类似的代码

#include <stdio.h>
main()
{
    int c, last;
    last = EOF;
    while ((c = getchar()) != EOF) 
    {
    if (c != ' ')
        putchar(c);
    if (c == ' ') 
        {
        if (last != ' ')
        putchar(c);
        }
    last = c;
    }
}

所以请有人解释一下，或者给我另一个带有正确解释的代码

谢谢

Answer 1

#include <stdio.h>
main()
{
    int c, last;
    last = EOF;

    /* while we get a char that isn't EOF */
    while ((c = getchar()) != EOF) {
        /* if it's not a space, print it */
        if (c != ' ')
            putchar(c);
        /* otherwise, if the previous char was not a space, print it */
        if (c == ' ') 
            if (last != ' ')
                putchar(c);
        last = c;
    }
}

这段代码可以更简单地写为

#include <stdio.h>
main()
{
    int c, last;

    /* while we get a char that isn't EOF */
    for (last = EOF; (c = getchar()) != EOF; last = c) {
        /* if it's not a space, print it */
        if (c != ' ')
            putchar(c);
        /* otherwise, if the previous char was not a space, print it */
        else
            if (last != ' ')
                putchar(c);
    }
}