Bulls and Cows - turning simple code into functions

Question

I'm trying to write a bulls and cows game. The program generates a 4-digit number and the user needs to guess the digits. If the user guessed a number and its position, it's a Bull. If the user only guessed the number, its a hit. I need to send it to our teacher in 3 files: function.h, function.c and main.c

I can't figure out how to separate the code into 3 different files. Every time I'm trying to make a function out of an action it doesn't work like the simple code. The teacher asked us to write a function for the code generator, the validating of the guess, the Bulls and the hits. I would appreciate any help.

The simple code:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main() {
    char code[5];
    char guess[5];
    int bulls, hits;
    int i, j;

    srand(time(NULL));

    for (i = 0; i < 4; i++) {
        code[i] = rand() % 9 + '0';
        for (j = 0; j < i; j++) {
            if (code[j] == code[i]) {
                i--;
            }
        }
    }

    for (i = 0; i < 4; i++) {
        printf("%c", code[i]);
    }
    putchar('\n');

    do {
        bulls = 0;
        hits = 0;
        
        scanf("%s", guess);

        for (i = 0; i < 4; i++) {
            for (j = i + 1; j < 4; j++) {
                if (guess[i] == guess[j]) {
                    printf("Invalid entry. The digits have to differ\n");
                    
                    break;
                }
            }
        }

        for (i = 0; i < 4; i++) {
            for (j = 0; j < 5; j++) {
                if (code[i] == guess[j]) {
                    if (i == j) {
                        bulls++;
                    } else {
                        hits++;
                    }
                }
            }
        }

        printf("%d bulls %d hits\n", bulls, hits);
    } while (bulls != 4);
    printf("you won");

    return 0;
}

function.h:

//A function that gets an array of 5 chars and contains the random 4 digits:
void GenerateCode (char code[], int i, int j);
//A function that gets an array of 5 chars and checks if the guess is valid:
int validateGuess (char guess[], int i, int j);
//A function that counts the bulls (if the user guessed the number and its position):
int CountBull(char code[], int len1, char guess[],int len2);
//A function that counts the hits (if the user guessed  only the number, not the position):
int CountHits (char code[], char guess[], int size);
//A function that prints the number of hits and bulls:
void PrintScore (int bulls, int hits);

Answer 1

Here. I improved it a bit.

function.h:

#pragma once

char code[5];
char guess[5];
int bulls, hits;
int i, j;

//A function that gets an array of 5 chars and contains the random 4 digits:
void GenerateCode();

//A function that gets an array of 5 chars and checks if the guess is valid:
int ValidateGuess();

//A function that counts the bulls (if the user guessed the number and its position):
int CountBullsAndHits(char code[], char guess[]);

//A function that prints the number of hits and bulls:
void PrintScore();

function.c:

#include "function.h"
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

void GenerateCode() {
    srand(time((void *)0));

    for (i = 0; i < 4; i++)
    {
        code[i] = rand() % 9 + '0';
        for (j = 0; j < i; j++)
        {
            if (code[j] == code[i])
            {
                i--;
            }
        }
    }

    printf("%s\n", code); // Remove this line if you want a true guessing game!
    printf("Guess the number! : ");
    ValidateGuess(guess);
    printf("You won!\n");
}

int ValidateGuess() {
    do {

    bulls = 0;
    hits = 0;

    scanf("%s", guess);

    for (i = 0; i < 4; i++)
    {
        for (j = i + 1; j < 4; j++)
        {
            if (guess[i] == guess[j])
            {
                printf("Invalid entry. The digits have to differ\n");

                break;
            }
        }
    }

    CountBullsAndHits(code, guess);
    PrintScore();
    } while (bulls != 4);
}

int CountBullsAndHits(char code[], char guess[]) {
    for (i = 0; i < 4; i++)
    {
        for (j = 0; j < 5; j++)
        {
            if (code[i] == guess[j])
            {
                if (i == j)
                {
                    bulls++;
                }
                else {
                    hits++;
                }
            }
        }
    }
}

void PrintScore() {
    printf("%d bulls, %d hits\n", bulls, hits);
}

main.c:

#include "function.h"

int main()
{
    GenerateCode();
    return 0;
}