c_exercises/1-9.c

#include <stdio.h>
int main() {
  int c;
  int prevb = 0;
  while ((c=getchar()) != EOF){
    if (c == ' ' && prevb == 1){
      continue;
    }
    if (c == ' '){
      prevb = 1;
      putchar(c);
    }
    else{
      prevb = 0;
      putchar(c);
    }
  }
  return 0;
}