Write a program to copy its input to its output, replacing each string of one or more blanks by a single blank.

　　编写这样一个程序，实现将输入流复制到输出流，但是要将输入流中多个空格过滤成一个空格。 

1.旗帜变量方法

#include 
     
       int main(void){  int c;  int inspace; 　//这里用了旗帜变量来过滤多余空格  inspace = 0;  while((c = getchar()) != EOF)  {    if(c == ' ')    {      if(inspace == 0)      {        inspace = 1;        putchar(c);      }    }     /* We haven't met 'else' yet, so we have to be a little clumsy */    if(c != ' ')    {      inspace = 0;      putchar(c);    }  }   return 0;}
     

2.保存上一个输入字符

Chris Sidi writes: "instead of having an "inspace" boolean, you can keep track of the previous character and see if both the current character and previous character are spaces:"

Chris Sidi 写道：“我们可以不用‘inspace’这样一个布尔型旗帜变量，通过跟踪判断上一个接收字符是否为空格来进行过滤。”

#include 
     
       /* count lines in input */intmain(){        int c, pc; /* c = character, pc = previous character */         /* set pc to a value that wouldn't match any character, in case        this program is ever modified to get rid of multiples of other        characters */         pc = EOF;         while ((c = getchar()) != EOF) {                if (c == ' ')                        if (pc != ' ')   /* or if (pc != c) */                                 putchar(c);                 /* We haven't met 'else' yet, so we have to be a little clumsy */                if (c != ' ')                        putchar(c);                pc = c;        }         return 0;}
     

3.利用循环进行过滤

Stig writes: "I am hiding behind the fact that break is mentioned in the introduction"!

#include 
     
       int main(void){        int c;        while ((c = getchar()) != EOF) {                if (c == ' ') {                       putchar(c);                       while((c = getchar()) == ' ' && c != EOF)                               ;               }               if (c == EOF)                       break; /* the break keyword is mentioned                               * in the introduction...                                * */                putchar(c);        }        return 0;}