Why are my if statements not working with strings in c++?

Question

I'm a newbie with c++, and I tried googling a solution but every one I came across was so different from the issue I was facing so I couldn't figure it out. The problem I'm having is my "if" statements are completely ignored when I run the .exe from powershell.

https://pastebin.com/aE6MiQig

#include <iostream>
#include <string>
using namespace std;

int main()
{
    string q;
    string w;
    string Bob;
    string Emily;
    {
        cout << "Who is this? ";
        cin >> q;
        if (q == Bob)
        {
            cout << "Hey there bro. ";
        }
        if (q == Emily)
        {
            cout << "Hi friend :) ";
        }
        else
        {
            cout << "Oh hey " << q << ", how are you? ";
        }
        cin >> w;
        cout << "Hey, that's " << w;
    }
    return 0;
}

When I input my name as "Bob" I should be seeing the message from the if statement "Hey there bro." but I am instead seeing the else statement, "Oh hey Bob, how are you?". Same goes when I input Emily. Only seeing the else statement.

I'm not getting any errors (running this in visual studio) so where am I messing this up?

Answer 1

Why not just compare directly to strings?

#include <iostream>
#include <string>

int main()
{
  std::string q;
  std::string w;
  std::cout << "Who is this? ";
  std::cin >> q;
  if (q == "Bob") // note the quotation marks around Bob
  {
      std::cout << "Hey there bro. " << std::endl;
  }
  else if (q == "Emily") // note the quotation marks around Emily
  {
      std::cout << "Hi friend :) " << std::endl;
  }
  else
  {
      std::cout << "Oh hey " << q << ", how are you? ";
      std::cin >> w;
      std::cout << "Hey, that's " << w << std::endl;
  }
  return 0;
}

Also, you should avoid using namespace std because it leads to namespace pollution. Instead, you can just put std:: in front of string, cin, cout, and endl as I've done above, or include a using statement for each of those specifically, like this:

using std::string;
using std::cin;
using std::cout;
using std::endl;

Answer 2

std::string comes with its own operator==, comparing the string's contents.

string Bob;
string Emily;

Well, now you have created two strings, both using the default constructor, and so both are empty strings (i. e. they both would compare equal to "").

You need to assign them a value:

string Bob("Emily");
string Emily("Bob");

I deliberately assigned them inverse! Try this piece of code and you'll discover yourself that it is the content that is relevant for comparison, not the variable's name...

Answer 3

You obtain the value for string q from the user and compare it to string Emily or string Bob , neither of which have any values assigned.

The problem I'm having is my "if" statements are completely ignored when I run the .exe from powershell.

Your if statements are not being ignored instead you're comparing string q to "".

You can give string Bob and string Emily initial values:

#include <iostream>
#include <string>

int main()
{
  std::string Bob = "Bob";
  std::string Emily = "Emily";
  std::string q;
}

This way you have something to compare the values you're getting from cin to:

#include <iostream>
#include <string>

int main()
{
  std::string Bob = "Bob";
  std::string Emily = "Emily";
  std::string q;

  std::cout<<"What is your name? ";
  std::cin>>q; //Obtain value from cin

  if(q == Emily){}//If q is Emily, then do something
}

You can read more about default variable values here and here.