Why are two getchar() functions used?

I'm trying to write a program which task is to get rid of extra whitespace in a text stream.

#include <stdio.h>

int main()
{
    int c;
    
    while( (c = getchar()) != EOF)
    {
        if(c == ' ')
        {
            putchar(c);
            while( (c = getchar()) == ' ' );
            
            if(c == EOF) break;
        }
        putchar(c);
    }
}

I know that getchar() function returns a new character each iteration and we store the character in the c variable, but I can't figure out why do we need to assign c variable to getchar() in the second while loop again.

The inner loop loops as long as it extracts spaces from the stream, effectively skipping them. The result is that, if you have a sequence of spaces, the first one will be printed, and the rest will be discarded.

You need to assign to c even there (as opposed to just doing something like while (getchar() == ' ');) because you'll reach a point where you extract a character that is not a space, so you need to remember what character it was to output it after the loop.