How can i maximize the performance of this C code?

I have written a code that basically asks the user to input 2 strings which it compares to find if they are anagrams or not. Im new to C and I know the code works fine but I don't know if it works well. I know its a relatively small code so the difference in performance would be negligible but I still want to learn

Someways I have thought of minimizing memory usage was by using data types like int8_t instead of int for a number that will never reach above 127. My while loops were a bunch of if statements before so that's one way I've faster. Also used && and II instead of extra if conditions. How else could I make the code work better?

Is it better for me to use put("...") instead of print("...\n") for the long string lines since they have no other purpose than displaying only strings? Is there a way to make the size of the array 26 instead of 128 since I am only concerned about the lower case alphabet? Are there any unwritten universal laws of coding that I need to know about to make my code more efficient?

/*  This code takes two input strings and detects whether they are anagrams. This is
    done by defining two functions, 'is_length() and 'is_anagram()'. is_length makes 
    sure both strings are a maximum of 10 strings. is_anagram() scans each character  
    on both strings and adds 1 to the elements corresponding to the character's  
    equivalent ASCII number. This produces two arrays of 128 elements which it  
    compares to check if the two words are anagrams   
 */

// Libraries used in the code 
#include <stdio.h>
#include <stdint.h>
#include <string.h>

void is_length(char str1[], char str2[]) {
    while (strlen(str1) > 10 || strlen(str2) > 10) {
        printf("\nMake sure the words are a maximum 10 characters\n");
        printf("Input two words:\n");
        gets(str1);
        gets(str2);
    }
}

int8_t is_anagram(char str1[], char str2[]) {   // Defining a function detects anagrams
    int8_t size1 = strlen(str1);                // Finding the sizes of the strings
    int8_t size2 = strlen(str2);

    if (size1 == size2) {                       // Checking if they are the same length
        int16_t str1Arr[128] = {};              // Defining an array with 128 elements
        int16_t str2Arr[128] = {};
        
        while (*str1) {
            str1Arr[(int16_t)*str1]++;          // Scanning each character in the    
            str1++;                             // string and adding 1 to the element  
        }                                       // corresponding their ASCII equivalent  
        while (*str2) {                          // number
            str2Arr[(int16_t)*str2]++;              
            str2++;
        }

        uint8_t i;
        for (i = 128; i--;) {                   // Comparing the string array elements
            if (str1Arr[i] != str2Arr[i]) {
                return 0;
            }
        }
        return 1;
    } else {
        printf("The words are not the same length so... \n");
        return 0;
    }
}

int main(void) {
    char word1[10] = {};                        // Defining variables for the strings
    char word2[10] = {};

    printf("Input two words: \n");              // Aquiring input strings from user
    gets(word1);
    gets(word2);
    is_length(word1, word2);                     // Recalling is_length()
                                   
    if ((is_anagram(strlwr(word1), strlwr(word2))) == 1) {    // Converting to lower case 
        printf("YES! The words are anagrams \n");           // and recalling is_anagram()
    } else {                                                  // to compare the two strings
        printf("NO, The words are not anagrams \n");
    }
    system("pause");
}