Need Suggestions/Comments

[maiden]

As a beginner in programming, I appreciate any comments/suggestions that could improve this program or make is more simpler and clean.

This program output a random number (0-100) and user will be prompt to input numbers including operator

somewhat like this:

SUM = ADDEND + ADDEND
DIFFERENCE = MINUEND - SUBTRAHEND
PRODUCT = FACTOR * FACTOR
QUOTIENT = DIVIDEND / DIVISOR

  /* ADDEND + ADDEND = SUM 
MINUEND - SUBTRAHEND = DIFFERENCE 
FACTOR x FACTOR = PRODUCT 
DIVIDEND / DIVISOR = QUOTIENT 
*/

#include <iostream>
#include <cstdlib>
#include <ctime>

double x;
double y;
double z;
char xOp; // Operator


// operator functions
int add()
{
	z = x + y;
	std::cout << z << "\n" << std::endl;
	return z;
}

int sub()
{
	z = x - y;
	std::cout << z << "\n" << std::endl;
	return z;
}

int mult()
{
	z = x * y;
	std::cout << z << "\n" << std::endl;
	return z;
}

int div()
{
	z = x / y;
	std::cout << z << "\n" << std::endl;
	return z;
}


// program main loop

int main()
{
	srand((time(0))); // seed random number

	while (true)
	{
		std::cout << " a = addition\ts = subtraction\t  m = mulplication\td = division\n\n";

		int rNumber = rand() % 100; // random number from 0-100
		
		char process[4] = { 'a', 's', 'm', 'd' };

		char processlist = process[rand() % 4];

		xOp = processlist;

		std::cout << rNumber;	// output a random number and process
		std::cout << "(" << processlist << ")\n"; 

		while (!(std::cin >> x)) // checking x
		{
			std::cout << "not integer\n";  // ignoring non-integer
			std::cin.clear();	// clearing the loop
			std::cin.ignore();	
		}

		std::cin >> xOp;			// checking Operator
		
		while (!(std::cin >> y)) // checking y
		{
			std::cout << "not integer\n";
			std::cin.clear();
			std::cin.ignore();
		}

		// checking operator
		if (processlist == 'a') // checking the Process Type
		{
			while (!(xOp == '+')) // checking if operator match to the process type
			{
				if (xOp == '-') { sub(); }
				else if (xOp == '*') { mult(); }
				else if (xOp == '/') { div(); }
				else { std::cout << "Operator not recognized\n"; }
				std::cout << " Process is not expected\n";
				goto SYSTEM_CLEAR;
			}

			add();	//function call

			if (z == rNumber ) // check if answer is equal to the random number
			{
				std::cout << z << " = " << rNumber << std::endl;
			}
			else {
				std::cout << z << " is not equal to " << rNumber << std::endl;
			}
		}
		else if (processlist == 's')
		{
			while (!(xOp == '-'))
			{
				if (xOp == '+') { sub(); }
				else if (xOp == '*') { mult(); }
				else if (xOp == '/') { div(); }
				else { std::cout << "Operator not recognized\n"; }
				std::cout << "Process is not expected\n";
				goto SYSTEM_CLEAR;
			}

			sub();
			
			if (z == rNumber ) // check if answer is equal to the random number
			{
				std::cout << z << " = " << rNumber << std::endl;
			}
			
			else {
				std::cout << z << " is not equal to " << rNumber << std::endl;
			}
		}
		else if (processlist == 'm')
		{
			while (!(xOp == '*'))
			{
				if (xOp == '-') { sub(); }
				else if (xOp == '+') { mult(); }
				else if (xOp == '/') { div(); }
				else { std::cout << "Operator not recognized\n"; }
				std::cout << "Process is not expected\n";
				goto SYSTEM_CLEAR;
			}
			
			mult();
			
			if (z == rNumber ) 
			{
				std::cout << z << " = " << rNumber << std::endl;
			}
			
			else {
				std::cout << z << " is not equal to " << rNumber << std::endl;
			}
		}
		else if (processlist == 'd')
		{
			
			while (!(xOp == '/'))
			{
				if (xOp == '-') { sub(); }
				else if (xOp == '*') { mult(); }
				else if (xOp == '+') { div(); }
				else { std::cout << "Operator not recognized\n"; }
				std::cout << "Process is not expected\n";
				goto SYSTEM_CLEAR;
			}

			div();

			if (z == rNumber ) 
			{
				std::cout << z << " = " << rNumber << std::endl;
			}
			
			else {
				std::cout << z << " is not equal to " << rNumber << std::endl;
			}
		}
		else
		{
			std::cout << "invalid operator";
		}

	SYSTEM_CLEAR:				// clear console 
		std::cin.get();
		std::cin.get();

		std::system("cls"); 
	}
	
}

[keskiverto]

Do it again, but now without the global variables and without goto.

[maiden]

Hi,

I had read some comments that using "goto" is bad programming because it will make a program hard to follow.
However, I been trying that before posting but failed.

It seems that goto is the easiest to solve this problem but knowing its bad I guess I need to avoid it..

Can you give me an alternative to goto statement?

[admkrk]

On a quick look, it looks like you are using goto in the same way that a function is used.
http://www.cplusplus.com/doc/tutorial/functions/
Scroll down to Functions with no type. The use of void and you will find a way to replace it.