suggestion game hangman

Hi, I'm trying to make a simple hangman game, where you must find the word.
I am blocked at this piece of code:
This do the job once, I want do this:
1-get char from stdin;
2-replace underscore with char given if exists;
3-add single char in a new char array;
4-when the word doesn't contain underscore anymore, stop.
Do you have some idea?

Code:

---

#include <stdio.h>
#include <string.h>

char *replaceChar ( char *string );
int main () {
        char s[] = "cane";
        char *newstr;
        //newstr = replaceChar( s );
       
        newstr = replaceChar( s );
        printf ( "%d\ns=%s\nnewstr=%s\n", strlen( s ), s, newstr);
       
}

char *replaceChar ( char *string ) {
        int x;
        int lung;
        char ch;
        lung = strlen ( string );
        printf ( "insert: " );
        ch = getchar();
               
        for ( x = 0; x < lung; x++ ) {
                if ( ch != string[x] ) {
                        string[x] = '_';
                }
        }
        return string;
}

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I would invest in some while loops right about now. The sort that execute until a certain condition is met, f. ex. the string does not contain any underscores. :)