C++ Tutorials - Absolute n00b spoonfeed

Here is a simple addition program.

The flow of the program is this:

Computer prints out "Hello and Welcome to Mars++'s addition calculator."

The computer asks for first and second number.
If the second Number is 0. Then the computer is to exit the program.
If the second Number is anything else besides 0. Then the program continues on the loop and asks you to input another first number.

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#include "stdafx.h"
#include <iostream>
using namespace std;

int main()
{
   double firstNumber, secondNumber;

   cout << "Welcome to Mars++'s Basic addition Calculator!" << endl;
   for(;;)
   {
      cout << "Enter First Number: ";
      cin >> firstNumber;
      cout << "Enter second Number(0 to Exit): ";
      cin >> secondNumber;
      if (secondNumber = 0)
      {
         cout << "Exiting" << endl;
         break;
      }
      cout << "Those two numbers added up is: " << firstNumber + secondNumber << endl;
      cout << endl;
   }
   return 0;
}



When you figure out what is wrong with the code. Create a new code that works, and tell what you changed to make it work. The program's objective should not change.

Got it, you need to change :

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if (secondNumber = 0)

to :

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if ( secondNumber == 0 )
{
etc...


This stops the program from reassigning the value, therefore making it unstoppably 0.

Hi Marss++,

Here's is the upgraded code to make the program fully functional.

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#include "stdafx.h"
#include <iostream>
using namespace std;

int main()
{
   double firstNumber, secondNumber;

   cout << "Welcome to Mars++'s Basic addition Calculator!" << endl;
   
      
   for(;;)
   {
    
      cout << "Enter First Number: ";
     cin >> firstNumber;
    
    
      cout << "Enter second Number(0 to Exit): ";
     cin >> secondNumber;
     int Answer;
     Answer = firstNumber + secondNumber;
    
      if (secondNumber == 0)
      {
         cout << "Exiting" << endl;
       break;
      
      }
      cout << "Those two numbers added up are: " << Answer << endl;
      cout << endl;
   }
   return 0;
}

I changed

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cout << "Those two numbers added up is: " << firstNumber + secondNumber

to this:

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cout << "Those two numbers added up are: " << Answer << endl;

with "Answer" = firstNumber + secondNumber

Then I added an = sign to this:

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      if (secondNumber == 0)

Hey Marss++,

I also meant to ask you: why didn't my compiler pick up on the missing '=' sign?

That would still be valid, because it would still return a boolean value, as I'm pretty sure positive integers are true and vice versa, so if you assign it a value, it still ends up procuring a boolean value for the if statement to use.

GREAT QUESTION


As you saw in antiRTFM's videos you can have the
'=' equals operator
'==' logical comparison operator


Both do seperate things.

Because of the flexibility of an if statement
the compiler does not know whether you are trying to make something equal another thing or if you are trying to evaluate something.

So wichever one you choose it's not going to tell you that you are wrong.

You may get a warning depending on your compiler, but that's not always the case.

So great question, the answer is that the compiler doesn't know whether or not your trying to evaluate or assign.



GREAT QUESTION!!

And good job fixing it.

may i humbly add to Marss++ what asib said;

An 'if' statement needs a boolean value in the parentheses. Whatever the heck you put in those parentheses will be looked at as something boolean, which means that its either 'true' or 'false'.

In c++, the number 0 (zero) will always be considered false. Anywhere you type 'false' in c++ you might as well type 0.

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bool dontLie = 0;
// assigning an int (zero number) to a boolean??? yup! 'false' is 0

Also, any number besides absolute 0 (like 1, 2, 34523, -1, -234, 2.8763, -0.00000000001 etc) evaluates 'true'.

Looking at the expression "secondNumber = 0" where we assign 0 to the variable secondNumber, after the assignment is done (as with any expression) the value of secondNumber is expressed for anyone to catch. The if statement will catch the secondNumber expression and look at it as its required boolean value for the if condition. secondNumber now has 0, so the condition evaluates as false.

Ahh good points, thanks for the feedback.

That is exactly correct.

Great job figuring these things out guys. You did a great Job!

Keep up the good work.

Muahahaha my first debug thing! 'twas very easy as it says!

So here is the code:

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    #include "stdafx.h"
    #include <iostream>
    using namespace std;

    int main()
    {
       double firstNumber, secondNumber;

       cout << "Welcome to Mars++'s Basic addition Calculator!" << endl;
       for(;;)
       {
          cout << "Enter First Number: ";
          cin >> firstNumber;
          cout << "Enter second Number(0 to Exit): ";
          cin >> secondNumber;
          if (secondNumber = 0)
          {
             cout << "Exiting" << endl;
             break;
          }
          cout << "Those two numbers added up is: " << firstNumber + secondNumber << endl;
          cout << endl;
       }
       return 0;
    }



If you your selves could not find the error at first sight let me show you where it is.Well, 'tis on line 16:

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          if (secondNumber = 0)

Oh noes! What is the solution Argio???

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          if (secondNumber == 0)

Argio how the hell does that work?

Simple = is a deceleration operator. Essentially if you want a value to change you tell the computer to change it by using this operator...
== Is a logic operator and in this case you tell the program to check for a value. If is a logic statement which would you rather have:

If the pie equals(==) the cake then
eat the pie

or

if WAIT A SEC COMPUTER! Make PIE equal(=) cake then eat it.

Does choice number 2 make any sense? This is why they made logic(comparison) operators.

lol Argio

^^^ lol

You just need to change the '=' to "==".


Old

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      if (secondNumber = 0)

New

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      if (secondNumber == 0)

Full Code

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#include "stdafx.h"
#include <iostream>
using namespace std;

int main()
{
   double firstNumber, secondNumber;

   cout << "Welcome to Mars++'s Basic addition Calculator!" << endl;
   for(;;)
   {
      cout << "Enter First Number: ";
      cin >> firstNumber;
      cout << "Enter second Number(0 to Exit): ";
      cin >> secondNumber;
      if (secondNumber == 0)
      {
         cout << "Exiting" << endl;
         break;
      }
      cout << "Those two numbers added up is: " << firstNumber + secondNumber << endl;
      cout << endl;
   }
   return 0;
}