Reverse a String In-Place

#include <stdio.h>

int custom_length(char *str){
    int length = 0;
    while ((length < 100) && (*str != '\0')){
        length ++;
        str ++;
    }
    return length;
}

void reverse_string(char *str) {
    // Your logic here
    int start = 0;
    int end = custom_length(str) - 1;

    while (start < end){
        char temp = *(str+start);
        *(str+start) = *(str+end);
        *(str+end) = temp;
        start ++;
        end --;
    }
}

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;
}