Cut excess whitespace from input and print to output
A few suggestions:


Extract the space removal to a function of its own.  It a repeatable task and despite this being a short program it's still good practice. Then all you have to do in main() is just pass in the input string. Here's a function I came up with:

void removeSpaces(char* source)
{
    for (char *i = source, *j = source; *j != 0;)
    {
        *i = *j++;
        if(*i != ' ') i++;
    }
    *i = 0;
}


Keep in mind that this method modifies the original string.
Change how you get input from the user.  I'd recommend either getting input via command line arguments, or using fgets().  It's safer those ways and easier to do in my opinion.  
If you decide to not use command line arguments, declare your function as:

int main(void)

Put the variable declarations to separate lines and initialize them to some value. From Code Complete, 2d Edition, p. 759:


  With statements on their own lines, the code reads from top to bottom,
  instead of top to bottom and left to right. When you’re looking for a
  specific line of code, your eye should be able to follow the left
  margin of the code. It shouldn’t have to dip into each and every line
  just because a single line might contain two statements.

You don't have to return 0 at the end of main(), just like you wouldn't bother putting return; at the end of a void-returning function. The C standard  knows how frequently this is used, and lets you not bother.


  C99 &amp; C11 §5.1.2.2(3)
  
  ...reaching the } that terminates the main() function returns a
  value of 0.