What should I do when one function finishes another one opens up?

I have a Problem. I'm Trying to make a regular Calculator and Shape's Area and Perimeter finder.It's a combination. I didn't start on my Shape's Area and Perimeter Finder. This is My main.cpp.

 #include <iostream>
 #include <string>
 #include "AAPO.h" // Its a Header File.

using namespace std;

void Calculators_Operation();

int main()
{
    string opera;
    cout << "Do you want Arithmetic Calculator or Area and Perimeter Calculator" 
    << endl;

    cin >> opera;
    if (opera == "Arithmetic Calculator" or "arithmetic calculator" or "AC")
    {
        Calculators_Operation();
    }
    return 0;
}

This is my Operation Chooser.

#include <iostream>
#include <string>
#include "Arithmetic Chooser.h"

using namespace std;

void Calculators_Addition();
void Calculators_Subtraction();
void Calculators_Multiplication();
void Calculators_Division();

void Calculators_Operation()
{
    string answera;
    cout << "What Operation do you Want?" << endl;
    cin >> answera;
    if (answera == "Addition" or "addition" or "+");
    {
        Calculators_Addition();
    };
    if (answera == "Subtraction" or "subtraction" or "-");
    {
        Calculators_Subtraction();
    };
    if (answera == "Multiplication" or "multiplication" or "*" or "x" or "X")
    {
        Calculators_Multiplication();
    };
    if (answera == "Division" or "division" or "/")
    {
        Calculators_Division();
    };
    return;
}

This is my AAPO.h.

#ifndef AAPO_H_INCLUDED
#define AAPO_H_INCLUDED

void Calculators_Operation();

#endif // AAPO_H_INCLUDED

My Addition.

#include <iostream>
#include <string>

using namespace std;

void calculators_Addition_2();
void calculators_Addition_3();
void calculators_Addition_4();
void calculators_Addition_5();

void Calculators_Addition()
{
    //ADDITION COMPLETE
    string numberadd;
    cout << "How much numbers do you want?" << endl;
    cin >> numberadd;
    if (numberadd == "2")
    {
        calculators_Addition_2();
        return;
    };
    if (numberadd == "3")
    {
        calculators_Addition_3();
        return;
    };
    if (numberadd == "4")
    {
        calculators_Addition_4();
        return;
    };
    if (numberadd == "5")
    {
        calculators_Addition_5();
        return;
    }
}

void calculators_Addition_2()
{
    int add11;
    int add12;
    int sum;
    cout << "Enter the first number" << endl;
    cin >> add11;
    cout << "Enter the second number" << endl;
    cin >> add12;
    sum = add11 + add12;
    cout << "The sum of the numbers are " << sum << endl;
    return;
}

void calculators_Addition_3()
{
    int add13;
    int add23;
    int add33;
    int sum2;
    cout << "Enter the First Number" << endl;
    cin >> add13;
    cout << "Enter the Second Number" << endl;
    cin >> add23;
    cout << "Enter the Third Number" << endl;
    cin >> add33;
    sum2 = add13 + add23 + add33;
    cout << "The Sum of the Numbers are " << sum2 << endl;
    return;
}

void calculators_Addition_4()
{
    int add14;
    int add24;
    int add34;
    int add44;
    int sum3;
    cout << "Enter the First Number" << endl;
    cin >> add14;
    cout << "Enter the Second Number" << endl;
    cin >> add24;
    cout << "Enter the Third Number" << endl;
    cin >> add34;
    cout << "Enter the Fourth Number" << endl;
    cin >> add44;
    sum3 = add14 + add24 + add34 + add44;
    cout << "The Sum of the Numbers are " << sum3 << endl;
    return;
}

void calculators_Addition_5()
{
    int a15;
    int a25;
    int a35;
    int a45;
    int a55;
    int sum4;
    cout << "Enter the First Number" << endl;
    cin >> a15;
    cout << "Enter the Second Number" << endl;
    cin >> a25;
    cout << "Enter the Third Number" << endl;
    cin >> a35;
    cout << "Enter the Fourth Number" << endl;
    cin >> a45;
    cout << "Enter the Fifth Number" << endl;
    cin >> a55;
    sum4 = a15 + a25 + a35 + a45 + a55;
    cout << "The Sum of the Numbers are " << sum4 << endl;
    return;
}

My Subtraction.

#include <iostream>

using namespace std;

void Calculators_Subtraction()
{
    int subractify;
    int subracta;
    int differencea;
    cout << "Type in the First Number!" << endl;
    cin >> subractify;
    cout << "Type in the Second Number!" << endl;
    cin >> subracta;
    differencea = subractify - subracta;
    cout << "The Difference is " << differencea << endl;
    return;
}

My Multiplication.

#include <iostream>
#include <string>

using namespace std;

void Calculators_Multiplication_2();
void Calculators_Multiplication_3();
void Calculators_Multiplication_4();
void Calculators_Multiplication_5();

void Calculators_Multiplication()
{
    string multicipia;
    cout << "How much numbers do you want?" << endl;
    cin >> multicipia;
    if (multicipia == "2" or "Two" or "two")
    {
        Calculators_Multiplication_2();
    };
    if (multicipia == "3" or "Three" or "three")
    {
        Calculators_Multiplication_3();
    };
    if (multicipia == "4" or "Four" or "four")
    {
        Calculators_Multiplication_4();
    };
    if (multicipia == "5" or "Five" or "five")
    {
        Calculators_Multiplication_5();
    };
    return;
}

void Calculators_Multiplication_2()
{
    int multi2a;
    int multi2b;
    int product2;
    cout << "Type in the First Number." << endl;
    cin >> multi2a;
    cout << "Type in the Second Number." << endl;
    cin >> multi2b;
    product2 = multi2a * multi2b;
    cout << "The Product is " << product2 << "." << endl;
    return;
}

void Calculators_Multiplication_3()
{
    int multi3a;
    int multi3b;
    int multi3c;
    int product3;
    cout << "Enter the First Number!" << endl;
    cin >> multi3a;
    cout << "Enter the Second Number!" << endl;
    cin >> multi3b;
    cout << "Enter the Third Number!" << endl;
    cin >> multi3c;
    product3 = multi3a * multi3b * multi3c;
    cout << "The Product is" << product3 << "." << endl;
    return;
}

void Calculators_Multiplication_4()
{
    int multi4a;
    int multi4b;
    int multi4c;
    int multi4d;
    int product4;
    cout << "Enter the First Number!" << endl;
    cin >> multi4a;
    cout << "Enter the Second Number!" << endl;
    cin >> multi4b;
    cout << "Enter the Third Number!" << endl;
    cin >> multi4c;
    cout << "Enter the Fourth Number!" << endl;
    cin >> multi4b;
    product4 = multi4a * multi4b * multi4c * multi4d;
    cout << "The Product of the Numbers are " << product4 << "!" << endl;
    return;
}

void Calculators_Multiplication_5()
{
    int multi5a;
    int multi5b;
    int multi5c;
    int multi5d;
    int multi5e;
    int product5;
    cout << "Enter the First Number!" << endl;
    cin >> multi5a;
    cout << "Enter the Second Number!" << endl;
    cin >> multi5b;
    cout << "Enter the Third Number!" << endl;
    cin >> multi5c;
    cout << "Enter the Fourth Number!" << endl;
    cin >> multi5d;
    cout << "Enter the Fifth Number!" << endl;
    cin >> multi5e;
    product5 = multi5a * multi5b * multi5c * multi5d * multi5e;
    cout << "The Product of the Numbers are" << product5 << "!" << endl;
    return;
}

My Division.

#include <iostream>

using namespace std;

void Calculators_Division()
{
    float divisia;
    float divisiab;
    float quotient;
    cout << "Enter the Divisor" << endl;
    cin >> divisia;
    cout << "Enter the Dividend" << endl;
    cin >> divisiab;
    quotient = divisia / divisiab;
    cout << "The Quotient of the Numbers are " << quotient << endl;
    return;
}

The Problem right now is that when addition finishes , subtraction starts. After Subtraction, Multiplication. After Multiplication, Division. After That the program ends. I'm sorry. Its just that I'm new to programming (Like one month).