trying to reverse string without string functions but not working in c

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

void main(void)
{
    char in[15], rev[15];

    printf("Enter a word (upto 15 letters): ");
    gets(in);
    
    for (int i = 0, j = 15; i < strlen(in); i++, j--)
    {
        rev[i] = in[j];
    }
    puts(rev);
}

Shows no error, just not working.
What am I doing wrong?

>Solution :

For starters according to the C Standard the function main without parameters shall be declared like

int main( void )

The function gets is unsafe and is not supported by the C Standard. Instead use either scanf or fgets.

The function strlen is a standard C string function. So according to the requirement you may not use it.

You are not reversing a string. You are trying to copy a string in the reverse order into another string.

The program can look the following way

#include <stdio.h>

int main(void)
{
    enum { N = 15 };
    char in[N] = "", rev[N];

    printf("Enter a word (upto %d letters): ", N - 1 );
    scanf( " %14s", in );

    size_t n = 0;
    while ( in[n] ) ++n;

    rev[n] = '\0';

    for ( size_t i = 0; i < n; i++ )
    {
        rev[n - i - 1] = in[i];
    }

    puts( rev );
}