Do and while loops.

[xcrossmyheartx]

I can't seem to get my do and while loop to work. For this assignment, I have to make a calculator that will keep looping with functions + - * and /. Here's what I have so far.

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

int main()
{

	double total = 0, number;
	string math;

	do
	{
	cout << "Current total is " << total << endl;
	cout << "Enter an operation: + - * / (or enter X to exit): " ;
	cin >> math; 
	cout << "Enter a number: " ;
	cin >> number;
	
	} while ((math != "x") && (math != "X") && (math == "+") && (math == "-")
		&& (math == "*") && (math == "/"));

	if (math == "+")
	{
		cout << total + number << endl;
	}

	if (math == "-")
	{
		cout << total - number << endl;
	}

	if (math == "*")
	{
		cout << total * number << endl;
	}

	if (math == "/")
	{
		cout << total / number << endl;
	}

}

So far, I have it asking for the mathematic symbol and then doing the equation with a number. However, it wont loop after one try! I can't figure out how to fix it. Any ideas?

[xcrossmyheartx]

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

int main()
{

	double total = 0, number = 0;
	string math;

	do
	{
		cout << "Current total is " << total << endl;
		cout << "Enter an operation: + - * / (or enter X to exit): ";
		cin >> math;
		cin.ignore();
		if (math == "X") break;
		cout << "Enter a number: ";
		cin >> number;
		cin.ignore();
	} while ((math != "x") || (math != "X") || (math == "+") || (math == "-")
		&& (math == "*") || (math == "/"));

	if (math == "+")
	{
		cout << (total + number) << endl;
	}

	else if (math == "-")
	{
		cout << (total - number) << endl;
	}

	else if (math == "*")
	{
		cout << (total * number) << endl;
	}

	else if (math == "/")
	{
		cout << (total / number) << endl;
	}
	
	

}

I can't get it to store the total and keep it as a running total. ARGH!

[xcrossmyheartx]

Anybody? :|

[filipe]

You only ever assign a value to total when you intialize it. Instead of total + number, you should say total += number. The same goes for the other operations.

[bluezor]

Single character constants should also be in ' 's as opposed to " ", i.e. '+', '-', '='.

Your while loop logic is also flawed - how can math be both + and * at the same time? I would make math a character as opposed to string as it should only be holding one operator as that is its intended use.

Your calculator also won't loop - once it somehow gets out of the do while loop and fulfills the if loops, that's the end of the program. I believe the if loops should be inside your do while loop.

[xcrossmyheartx]

With some help from a friend, I have it adding up the numbers, but it's inputting odd values and formatting.
Here's the code:

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

int main()
{

	double total = 0, number = 0;
	char math;

	do
	{
		cout << "Current total is " << total << endl;
		cout << "Enter an operation: + - * / (or enter X to exit): ";
		cin >> math;
		cin.ignore();
		if (math == 'X') break;
		cout << "Enter a number: ";
		cin >> number;
		cin.ignore();
	
	if (math == '+')
	{
		total = total + number;
		cout << total + number << endl;
	}

	else if (math == '-')
	{

		total = total - number;
		cout << (total - number) << endl;
	}

	else if (math == '*')
	{
		total = total * number;
		cout << (total * number) << endl;
	}

	else if (math == '/')
	{
		total = total / number;
		cout << (total / number) << endl;
	}
	
	} while ((math != 'x') || (math != 'X') || (math == '+') || (math == '-')
		|| (math == '*') || (math == '/'));

	

}

The input will be like:
[img] http://i27.tinypic.com/2z9il9h.jpg [/img]

[filipe]

How about putting all those if statements inside the loop? And if you want to use character literals as bluezor suggested, you need to change variable math's type to char.

[xcrossmyheartx]

Ok, I put them into the loop and I also changed the variable type. I don't understand why I'm getting the odd formatting between with the number though.

[filipe]

Just think for a minute. You're changing total's value (you really should use the proper operator as I suggested, so you don't have to type "total" twice) and then, instead of just outputting total, you're outputting the result of performing the operation again.

So, instead of, say cout << total + number << endl; you really want to say cout << total << endl;

[xcrossmyheartx]

I'm sorry but that makes absolutely no sense to me.

If I change total + number to total += number, I get an error that reads:
STD::basic_ostream<_Elem, _Traits<

I'm trying really hard to reread and understand all of this but isn't making sense to me.

You only ever assign a value to total when you intialize it. Instead of total + number, you should say total += number. The same goes for the other operations.

I tried changing them, and I get that error.

[filipe]

Let me be clear. You should change this:

total = total + number;

to this:

total += number;

It means exactly the same thing; operator+= just makes things easier and more direct.

[xcrossmyheartx]

Oh okay, I didn't realize I had the formula written twice. Forgive me, I've been wanting to rip my hair out for hours :/

I've made the changes, but it's still outputting in the awkward way, though displaying the right answer.

Enter sign
Enter number
x
Total is x

Also, for some reason, when I try and add a line of code that will detect when the user divides and the output gives me -1.#IND.

else if ((math == '/') && (number == '0'))
	{
		cout << "No." << endl;
	}
	

I'm having a bad night.

[bluezor]

For numbers, you don't need the ' 's.

' ' is for characters.
" " is for strings.

[xcrossmyheartx]

Okie, removed them and still get the funky output.

[firedraco]

I would suggest just putting the number check inside of this else if():

else if (math == '/')
{
	if(/*number is 0*/) {
		//oh crap
	} else { //we are ok
		total = total / number;
		cout << (total / number) << endl;
	}
}

[filipe]

but it's still outputting in the awkward way

What exactly do you think is awkward about it?

Also, for some reason, when I try and add a line of code that will detect when the user divides and the output gives me -1.#IND.

Notice this:

number == '0'

number is a double, not a char. So we test for the double 0.0, not for the character literal '0':

number == 0.0

Remember to test before you perform the division.

[xcrossmyheartx]

http://i32.tinypic.com/2w69xq9.jpg

[filipe]

If you don't want that output, then remove the corresponding line from the if statements. In case you're in doubt, it's this line:

cout << total << endl;

[xcrossmyheartx]

Wow, I feel so stupid. I made such a mistake taking this class online.. my instructor seriously sent out an e-mail saying we're only allowed to ask 3 questions the entire term.

Thank you so much filipe.. I really should pay you for this! Haha.

Here's what I'm getting, along with my code, with the 0.0

http://i32.tinypic.com/30ag7ba.jpg

This is before I took out the repeated input I was trying to get rid of too. So don't mind that part :P

[filipe]

I'm glad to help.

To fix that you need to test for that 0.0 before performing division. The statement you just added will never be executed if math == '/'. You should do what firedraco suggested.