Compare getline() to predetermined variable in an 'If' statement - c++

Question

First off, I just started learning C++, so please forgive me if I titled this incorrectly, or I don't know what something means. If you do answer this question, please don't use all those crazy vocabulary words that I wouldn't know. Thanks :).
I am currently (trying) to make a calculator, that give you a choice to either add subtract, multiply, or divide. I know this doesn't seem like something that would be very helpful, but of the things I have done, I have learned a lot from it.
Here is the code that I have right now:
#include <iostream>
#include <string>
using namespace std;
int add()
{
int x;
int y;
int sum;
cout << "Enter the value for x: ";
cin >> x;
cout << "Enter the value for y: ";
cin >> y;
sum = x + y;
cout << x << " + " << y << " = " << sum << endl;
}
int subtract()
{
int x;
int y;
int difference;
cout << "Enter the value for x: ";
cin >> x;
cout << "Enter the value for y: ";
cin >> y;
difference = x - y;
cout << x << " - " << y << " = " << difference << endl;
}
int multiply()
{
int x;
int y;
int product;
cout << "Enter the value for x: ";
cin >> x;
cout << "Enter the value for y: ";
cin >> y;
product = x * y;
cout << x << " * " << y << " = " << product << endl;
}
int divide()
{
int x;
int y;
int quotient;
cout << "Enter the value for x: ";
cin >> x;
cout << "Enter the value for y: ";
cin >> y;
quotient = x / y;
cout << x << " / " << y << " = " << quotient << endl;
}
int main()
{
int Add, Subtract, Multiply, Divide;
string str;
cout << "Add, Subtract, Multiply, Divide?: ";
getline(cin, str);
if (str == (cin, add));
cout << "Starting process " << str << "..." << endl;
add();
getline(cin, str);
if (str == (cin, "subtract"));
cout << "Starting process " << str << "..." << endl;
subtract();
}
The Issue I am having, is in the main() part. I want the program to read the user input via getline and then have it compare it to a predetermined variable. Then, I tried to make an if statement, that, if the user input was for instance "add", then the if statement reads that, and then runs my add function.
I got as far as the getline part, but as you can see, the if statement does nothing. I was thinking it might be something like:
if (str == "add")
cout << "Starting Process" << str << "..." << endl;
add();
All that got me was some errors. I'm not sure how to construct the if statement, and any help would be greatly appreciated.
Thanks,
Nick

Answer 1

So, I did some research, and I got this to finally work. I apologize if this caused you any inconvenience. I can see though, that this is a very active and nice community. I will make sure to come back to it as a "first line of defence". Here is my final code:
#include <iostream>
using namespace std;
void add()
{
int x;
int y;
int sum;
cout << "Enter the value for x: ";
cin >> x;
cout << "Enter the value for y: ";
cin >> y;
sum = x + y;
cout << x << " + " << y << " = " << sum << endl;
}
void subtract()
{
int x;
int y;
int difference;
cout << "Enter the value for x: ";
cin >> x;
cout << "Enter the value for y: ";
cin >> y;
difference = x - y;
cout << x << " - " << y << " = " << difference << endl;
}
void multiply()
{
int x;
int y;
int product;
cout << "Enter the value for x: ";
cin >> x;
cout << "Enter the value for y: ";
cin >> y;
product = x * y;
cout << x << " * " << y << " = " << product << endl;
}
void divide()
{
int x;
int y;
int quotient;
cout << "Enter the value for x: ";
cin >> x;
cout << "Enter the value for y: ";
cin >> y;
quotient = x / y;
cout << x << " / " << y << " = " << quotient << endl;
}
int main()
{
int Add, Subtract, Multiply, Divide;
string str;
cout << "Add, Subtract, Multiply, Divide? (Letters are case sensitive): ";
getline(cin, str);
if (str == "Add")
{
cout << "Starting Process " << str << "..." << endl;
add();
}
//getline(cin, str);
if (str == "Subtract")
{
cout << "Starting process " << str << "..." << endl;
subtract();
}
//getline(cin, str);
if (str == "Multiply")
{
cout << "Starting process " << str << "..." << endl;
multiply();
}
//getline(cin, str);
if (str == "Divide")
{
cout << "Starting process " << str << "..." << endl;
divide();
}
}