Thread: Why is this program not doing what I want it to do.

First, indentation makes for much easier code reading.

Code:

#include <stdio.h>

int getandshort(char store[], char hold[]);
int nullit(char arr[]);
int main()
{
  int i;
  char storeline[100];
  char holdspace[100];

  nullit(storeline);
  nullit(holdspace);
  getandshort(storeline, holdspace);

  for (i = 0; i < 100; ++i)
    printf("%c", storeline[i]);
  return 0;
}

int getandshort(char store[], char hold[])
{
  int i;
  int c;
  for (i = 0; (c = getchar()) != '\n' && c != EOF; ++i) {
    if (c != ' ' || c == ' ' && store[i - 1] != ' ')
      store[i] = c;
  }
  store[i] = '\0';
}

int nullit(char arr[])
{
  int i;
  for (i = 0; i < 100; ++i) {
    arr[i] = '\0';
  }
}

Second, turn up the warnings.

Code:

$ gcc -Wall foo.c
foo.c: In function ‘getandshort’:
foo.c:25:30: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
   25 |     if (c != ' ' || c == ' ' && store[i - 1] != ' ')
      |                     ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
foo.c:29:1: warning: control reaches end of non-void function [-Wreturn-type]
   29 | }
      | ^
foo.c: In function ‘nullit’:
foo.c:37:1: warning: control reaches end of non-void function [-Wreturn-type]
   37 | }
      | ^

- both your functions could be declared void rather than int
- adding ( ) helps to make sense of your complicated logic.

The two problems are:
1. store[i-1] is off the end of the array when i = 0
2. You increment i for every character, not every valid character.