Random number

so basically, this is my program and i get a strange output,
as you can probably already tell, I'm new.
The output : some strange number after the "The answer is: " , I think it may be a memory address or something.
(NO CLUE! )

#include <iostream>

using namespace std;

// PROTOTYPES:
int cls (int x);
int multiply(int x,int y);
int division(int x,int y);
int add(int x,int y);
int subtract(int x,int y);

int main(){
//VARIABLES
int counter = 0;
int y;
int x;
int ui;
int ui2;

do {
counter ++;
cls(counter);

cout << "1) ENTER A NUMBER TO ADD\n";
cout << "2) ENTER A NUMBER TO SUBTRACT\n";
cout << "3) ENTER A NUMBER TO MULTIPLY\n";
cout << "4) ENTER A NUMBER TO DIVIDE\n\n";
cout << " PRESS 1,2,3 or 4 depending on what you want:" <<endl;
cin >> ui2;

if (ui2 == 1 ) {

cout << "ENTER A NUMBER TO ADD\n";
cin >> x;

cout << "ENTER SECOND NUMBER TO ADD\n";
cin >> y;
cout << add(x,y);
}else if (ui2 == 2) {

cout << "ENTER A NUMBER TO SUBTRACT\n";
cin >> x;
cout << "ENTER SECOND NUMBER TO SUBTRACT\n";
cin >> y;
cout << subtract(x,y);
}else if (ui2 == 3) {


cout << "ENTER A NUMBER TO MULTIPLY\n";
cin >> x;
cout << "ENTER SECOND NUMBER TO MULTIPLY\n";
cin >> y;
cout << multiply(x,y);

} else if (ui2 == 4) {


cout << "ENTER A NUMBER TO DIVIDE\n";
cin >> x;
cout << "ENTER SECOND NUMBER TO DIVIDE\n";
cin >> y;
cout << division(x,y);
} else {

cout << "INVALID INPUT!\n";
}


cout << "\nWOULD YOU LIKE TO RESTART?" << endl;
cout << "\nEnter 1 for yes and 2 for no:" << endl;
cin >> ui;

}while(ui == 1 );


// FUNCTIONS HERE!
}
int add(int x,int y) {

cout << "The answer is : \n" << x + y << endl;
}
int subtract(int x, int y){

cout << "The answer is : \n" << x-y << endl;
}

int multiply(int x, int y) {

cout << "The answer is : \n" << x*y << endl;
}
int division(int x, int y) {

cout << "The answer is : \n" << x/y << endl;
}
int cls (int x) {
if (x = 5) {
system("CLS");
return 0;
}
}

First, I'm going to get this out of the way:

And that seems to list the source of your problem, they don't return a value, so you don't have any control what value they do send back.

Consider getting an updated (=more programmer and novice friendly) compiler. (The "dev-cpp" IDE from bloodshed includes an ancient compiler.)