#include <stdio.h>
char *no_space(char *);

int main(void) {

  char *strin = "HELLO WORLD";

  printf("%s\n", strin);
  printf("%s\n", no_space(strin));

  return 0;
}

char *no_space(char *strin){

 int i = 0, c = 0;

    for ( ; strin [i] ; i++ ){

     if ( strin[i] != ' ' )

        strin[c++] = strin[i];

    }

  strin[c]= '\0';

 return strin;
}