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;
}

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.