I am currently studying c programming, but I'm at a very basic level. So for practice I made a program that reads a string and inverts it. I want to know if the code is readable and how can I improve it.

    /* 
    * Goal: Given a string, invert it, then print the result.
    * Author: Lúcio Cardoso
    */

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

    /*This is the size of the arrays in this program. It's better to use a          
    constant, because makes easier to modify the arrays' size, if needed.*/
    #define NUM 200


    void invert(char *s) //Fucntion responsible for inverting the string.
    {
        char aux[NUM];
        int i, j, n; //These variables are all used to control the for loops.

        /*This loop will read the size of the array's string, that's why
        strlen(s) - 1 is used. We don't need to read all contents
        from the array, just the string. As we read the s[] backwards,
        its content is stored in aux[n]. In this case, from zero to the
        size of s[]'s string - 1. Minus 1 is used because we read it from ZERO,
        not i. */
        for (i = strlen(s) - 1, n = 0; n < strlen(s), i >= 0; i--, n++) {
            aux[n] = s[i];
        }

        printf("Included with the super mojo from the string inverter, ");
        printf("this is the result: ");

        //This for loop reads all the content from the aux array, and print it.
        for (j = 0; j < strlen(s); j++) {
            printf("%c", aux[j]);
        }
    }

    int main(void)
    {
        char string[NUM];

        printf("\nWelcome to the super, duper string inverter!\n");
        printf("If you want to see some magic, enter a string:\n>");
        gets(string); //Reads the string.

        //Now, we only need to call the function with string[] as a parameter.
        invert(string);

        return 0;
    }