Reverse a String In-Place

#include <stdio.h>

void reverse_string(char *str) {
    int i=0;
    while(str[i]!='\0')i++;
    int s=0,e=i-1;
    while(s<e)
    {
        char buf=str[s];
        str[s++]=str[e];
        str[e--]=buf;
    }
}

int main() {
    char str[101];
    fgets(str, sizeof(str), stdin);

    // Remove newline
    int i = 0;
    while (str[i] != '\0') {
        if (str[i] == '\n') {
            str[i] = '\0';
            break;
        }
        i++;
    }

    reverse_string(str);
    printf("%s", str);
    return 0;
}