Calculator in C++

Here is my functions based calculator in C++.
any suggestions!!

This is a multi-all-in-one function calling program.
in this program the user will be able to call different
programs using if else statments.
#include <iostream>

using namespace std;

// this is the addition function.
int addition (int a, int b)

int adding_operation;
adding_operation = a + b;
return adding_operation;

//this is the subtraction function.
int subtraction (int c, int d)

int subtraction_operation;
subtraction_operation = c - d;
return subtraction_operation;

//this is the multiplication function.
int multiplication (int e, int f)

int multiplication_operation;
multiplication_operation = e * f;
return multiplication_operation;

//this is the division function.
int division (int g, int h)

int division_operation;
division_operation = g / h;
return division_operation;


//this is the remainder function.
int remainder (int i, int j)

int remainder_operation;
remainder_operation = i % j;
return remainder_operation;


int main()

    //this is the conditions part of the program.
    char op;
    int x;
    int y;
    cout<<" input operation type: (avilable types are +, -, *, /, %)"<<endl;
    cout<<"enter the first value (any integer number)"<<endl;
    cout<<"enter the second value (any integer number)"<<endl;

    //this is the apply condition section of the program.
        case '+':
            int excute_addition;
            excute_addition = addition(x, y);
            cout<<"The result is:" << excute_addition << '\n';
        case '-':
            int excute_subtraction;
            excute_subtraction = subtraction(x, y);
            cout<<"The result is:" << excute_subtraction << '\n';
        case '*':
            int excute_multiplication;
            excute_multiplication = multiplication(x, y);
            cout<<"The result is:" << excute_multiplication << '\n';
        case '/':
            int excute_division;
            excute_division = division(x, y);
            cout<<"The result is:" << excute_division << '\n';
        case '%':
            int excute_remainder;
            excute_remainder = remainder(x, y);
            cout<<"The result is:" << excute_remainder << '\n';
            cout<<"invaled operation"<< '\n' <<endl;
    //looping the program;
    int user_decision;
    cout<<"Would you like to run the program again? (1 for yes, 2 for no)"<<endl;
    if ( user_decision == 1 ){
        return main();
    }else if( user_decision == 2 ){
        return 0;