Simple C++ calculator program

Code:

#include <iostream>
#include <stdlib.h>

using namespace std;

int add(int a, int b);
int sub(int a, int b);
int multi(int a, int b);
int divi(int a, int b);
int mod(int a, int b);

int main(){
 int a,b,choose;
 
 system("cls");
 
 cout << "\t\t=================================\n";
 cout << "\t\tWelcome to the simple calculator!\n";
 cout << "\t\t=================================\n\n\n";
 
 cout << "--------------------------------------------------------------\n";
 cout << "-> Enter the first number\t: ";
 cin >> a;
 cout << "--------------------------------------------------------------\n";
 cout << "-> Enter the second number\t: ";
 cin >> b;
 cout << "--------------------------------------------------------------\n";
 
 system("cls");
 
 cout << "--------------------------------------------------------------\n";
 cout << "What do you want to do? \n";
 cout << "--------------------------------------------------------------\n\n";
 cout << "--------------------------------------------------------------";
 cout << "1. Addition\n";
 cout << "2. Subtraction\n";
 cout << "3. Multiplication\n";
 cout << "4. Divition\n";
 cout << "5. Modulo\n";
 cout << "--------------------------------------------------------------\n\n";
 cout << "--------------------------------------------------------------\n";
 cout << "Type the number of your choice: ";
 cin >> choose;
 cout << "--------------------------------------------------------------\n\n";
 
 if (choose == 1){
  cout << "--------------------------------------------------------------\n";
  cout << "The output is: " << add(a,b) << endl;
  cout << "--------------------------------------------------------------\n";
 }
 else if (choose == 2) {
  cout << "--------------------------------------------------------------\n";
  cout << "The output is: " << sub(a,b) << endl;
  cout << "--------------------------------------------------------------\n";
 }
 else if (choose == 3){
  cout << "--------------------------------------------------------------\n";
  cout << "The output is: " << multi(a,b) << endl;
  cout << "--------------------------------------------------------------\n";
 }
 else if (choose == 4) {
  cout << "--------------------------------------------------------------\n";
  cout << "The output is: " << divi(a,b) << endl;
  cout << "--------------------------------------------------------------\n";
 }
 else if (choose == 5) {
  cout << "--------------------------------------------------------------\n";
  cout << "The output is: " << mod(a,b) << endl;
  cout << "--------------------------------------------------------------\n";
 }
 else {
  cout << "--------------------------------------------------------------\n";
  cout << "Your input is incorrect, try again!\n";
  cout << "--------------------------------------------------------------\n";
  system("pause");
  main();
 }
 
 system("Pause");
}

int add (int a, int b){
 return a+b;
}

int sub (int a, int b){
 return a-b;
}

int multi(int a, int b){
 return a*b;
}

int divi(int a, int b){
 return a/b;
}

int mod (int a, int b){
 return a%b;
}