В main.c
#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include "functions.h"
В funcions.h
#ifndef FUNCTIONS_H
#define FUNCTIONS_H

bool checkUnique(int,char,bool);

bool IntNumber(char,int,int);

void replace(int*, int,int);

void printNum(int, int);

#endif
В functions.c
#include <stdio.h>
#include <stdbool.h>
#include <string.h>

bool checkUnique(int length,char a[10],bool verity){
int k = 0;
for(int i = 0;i<length-1;i++)
if (a[i]==a[i+1])
k++;
if (k==length-1 && length !=1)
verity = false;
return verity;
}

bool IntNumber(char enter[10],int number[10],int length){
if (length > 10||length < 1)
return false;
for (int i = 0;i<length;i++){
number[i] = enter[i]-'0';
if (number[i] < 0||number[i] > 9)
return false;
}
return true;
}

void change(int*num, int firstIndex,int secondIndex){
int t = num[firstIndex];
num[firstIndex] = num[secondIndex];
num[secondIndex] = t;
}

void printNum(int num[10],int length){
FILE*out;
out = freopen("out.txt","a",stdout);
for (int i = 0;i < length;i++)
printf("%d",num[i]);
printf("\n");
fclose(out);
}