C++ tutorials question about variables

[hit45]

I'm new on this stuff for the most part. I'm practicing using the tutorials on this site; Documentation-C++Tutorials-Variables/data types.

I'm trying the one that has you practice the variables ( a=5, b=2, a = a+1, result = a-b).

I don't understand why "a" will equal more than one variable! Shouldn't it really be written as "a=5, b=2, c=a+1 ???

I tried it both ways and it worked both ways. Is this typical or is there something wrong. I thought when I first read it that an "error" would have appeared.

Any thoughts?

[Disch]

variables can change, that's the whole point. They're like "containers" for information.

When you reassign a variable, the old value is lost.

int a;

a = 5;  // 'a' is 5

a = 3;  // now the 5 is lost, and 'a' becomes 3 

[jsmith]

a = a + 1 just says to set a to the value of 1 + the current value of a. In other words, increment it by one.

[hit45]

Ok, I see somewhat, what you mean. But then if 'a = 5' is lost after the second 'a' is reassigned, then how does the program know that the 'a' in the second statement is '5' and not some other integer?

[Disch]

I'm not sure I understand your question.

Think of variables as a kind of box. They can hold a number, but they can only hold one number at a time.

a = 5;  // this puts the number 5 into the variable 'a'

a = 3;  // this puts the number 3 into the variable 'a' (replacing the number 5)

// the compiler doesn't need to know about the 5 here -- the 5 is gone forever

a = a + 1;  // this takes the number currently in 'a' (3), adds 1 to it (4), and puts
   // the result in 'a'  -- so that 'a' now holds the number 4 

[hit45]

Ok, I think it's just a brain fart. :)

So it doesn't just reassign "a" , but takes the original assignment, and then does what you want it to do after that. In this case, it would mean that " the original 'a' was '5', and now I want it to be
the 'original + 1'

If that makes since to you. It does to me!

Thanks for the feed back.

[hit45]

How about one more question!
At the end of the program, it has me write "return 0'. When I do this, the little black box that should appear on my screen with the current example ( I guess the DOS window) doesn't appear. It blinks out quickly.

But when I use ' system ("pause"); then it shows up and I can read what it says (the result of the program) until I hit another key to continue.

Is "return 0" used for the actual program in use and "system ("pause") just for practicing?

[Disch]

- It's not a DOS window ;P It a command prompt.

- Instead of system("pause"), you should use a safer/cleaner alternative like cin.get();

- return exits the current function. In this case, main() is the current function. When main exits, the program ends and the window closes.

- system("pause"); and cin.get(); are ways to wait for user input, so that the program remains open until the user is ready for it to close.

[hit45]

;p good one. The tutorial uses that as the example. I learned about 'system ("pause") from; "cppgameprogramming.com" and tried it and it left the command prompt open.

I see how the "cin.get();" is cleaner. Less info on the prompt.

Maybe the tutorial needs to be updated?

Thanks for the help.