"The C Programming Language", 2nd edition, Kernighan and Ritchie

Answer to Exercise 1-9, page 20

Solutions by Richard Heathfield and Chris Sidi

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


#include <stdio.h>

int main(void)
{
  int c;
  int inspace;

  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;
}


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:" 


#include <stdio.h>

/* count lines in input */
int
main()
{
        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;
}

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