Making a Simple Program

• A Simple Program
• Some Prerequisites
• Let’s talk about Functions!

A Simple Program

Here’s the Problem:

Suppose that you have been given an assignment to do a lot of calculations at once. However, you do not have a calculator to do the job. Your boss tells you to simply make one in your PC, given your expertise in the subject. You now have the abominable job of making a calculator that you will only be using once.

Some Prerequisites

Okay, so here is how I think I will be writing the program for this:

• Make a starting menu, giving me all the options
• For each keybutton pressed, it should give me options on how to continue my calculations, or to rather clear it all to zero.

Let’s talk about Functions!

Functions, are, well, this:

Functions allow to structure programs in segments of code to perform individual tasks. -CPlusPlus

Said in a simple way, functions are operations that, if given the proper parameters, you can call at any point of the program to do a certain task. You can think of it as a shortcut to lengthy programs. Here’s why I think it helps:

So let’s just assume that this calculator that I will be doing will have just addition.

Then the code should look something like this, right?:

#include <iostream>
using namespace std;
int main()
{
	int a,b,menu=0; 
	/* You'll know what I'm doing in a short while. Oh, and BTW, this is a thing. You can declare similar 		variables together with a comma*/
	while (menu==0)
	{	cout<<"Specify the two numbers to add:"<<endl;
		cin>>a>>b;
		cout<<a+b;
		cout<<"Do you want to exit?If yes, press 1. If not, press 0"<<endl;
		cin>>menu;
	}
return 0;
}

Right?

But we can reach a greater level of efficiency with functions. This was a simple program; we can cheat around and use while loops. I doubt we’d be able to do that with many others.

A function is written like this:

data_type function_name(data-type-of-parameter); //This is the declaration section of it
function_name(parameter)
{
 	//Some code
}

Therefore, we should be able to manipulate the program by making it more like this:

#include <iostream>
using namespace std;
void menu(int); //Declaring a function that won't exactly return anything, and takes an int for a parameter
int param;
int main()
{
	param = 0;
	
	do{	
		menu(param);
		cout<<"Do you want to exit? If yes, press 1, otherwise, press 0";
		cin>>param;
	}while(param==0);
return 0;
}
void menu(int param)
{
	int a,b;
	if(param==0)
	{	cout<<"Specify the two numbers to add:"<<endl;
		cin>>a>>b;
		cout<<a+b<<endl;
	}
	else if(param==1)
	{
		cout<<"Thank you for using our calculator"; //Obligatory useless message
	}
	else cout<<"Invalid request"<<endl;
}

Believe me when I say this has a difference on how good the program looks.

So, let’s get started on the whole program, shall we?

Here is the code:

#include <iostream>
using namespace std;
void menu(int); 
int showMenu(void);
int param;
int main()
{ 
	
	showMenu();
	while(param!=0)
	menu(param);
	return 0;
}
void menu(int param)
{
	float a,b;
	if(param==1)
	{	cout<<"Specify the two numbers to add:"<<endl;
		cin>>a>>b;
		cout<<a+b<<endl;
		showMenu();
	}
	else if(param==0)
	{
		cout<<"Thank you for using our calculator"; 
	}
	else if(param==2)
	{
		cout<<"Specify the two numbers to subtract:";
		cin>>a>>b;
		cout<<a-b;
		showMenu();
	}
	else if(param==3)
	{
		cout<<"Specify the two numbers to multiply:";
		cin>>a>>b;
		cout<<a*b;
		showMenu();
	}
	else if(param==4)
	{ 		
		cout<<"Specify the two numbers to divide:";	
		cin>>a>>b;
		cout<<a/b;
	showMenu();
	}		 
	else cout<<"Invalid request"<<endl;
}
int showMenu(void)
{
cout<<"1. Add two numbers:"<<endl;
cout<<"2. Subtract two numbers:"<<endl;
cout<<"3. Multiply two numbers:"<<endl;
cout<<"4. Divide two numbers:"<<endl;
cout<<"0. Exit"<<endl;
cin>>param;
return param;
}

So there ya have it. Making a Calculator using functions. It would definitely be better if we could somehow pause the program (more on that later).