#include <stdio.h>
void replace_first_char(char *s, char ch, char new_ch) {
int i = 0;
while (s[i] != '\0') {
if (s[i] == ch) {
s[i] = new_ch;
break;
}
i++;
}
}
int main() {
char s[30] = "c programming";
replace_first_char(s, 'm', 'n');
puts(s);
}
/*
run:
c progranming
*/