Reading

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Stack
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A stack is a very simple container 

it is first in last out (FILO)

imagine you have to store some numbers  and you write them on a plate and stack them up
you add 5, then 50 , then 7
you now have 3 plates the bottom one has 5 written on it, on top of that is the plate with 50 on it and finally on top is the plate with 7


this is a stack , the rules are you can only add or remove to the top of the stack. 
you can add as many values as you like but the only one you can take off is the one at the top. 
if you want to get to the one at the bottom of the stack you must remove the top plate over and over until you get to the last one

so this is why it is FILO   the first value inserted is the last one to be removed.



adding a value is called a PUSH 
removing a value is called a POP



a stack is commonly the first type of container to be disucssed in programing as it is the simplest to implement


all you need is an array and an integer counter








File: simple_stack.cpp 





class stack
{
	int data[10];
	int couter;
	stack() { counter =0;}

	int Top()
	{
		if (counter ==0 ) 
			throw "the stack is empty";

		return data[counter-1];
	}
	void Push(int value) 
	{
		if (counter < 10)
		{
			data[counter]=value;
			counter ++;

		}
	}

	void Pop()
	{
		if (counter >0)
			counter --;
	}

	int Size() {return counter;}
};



int main()
{

	stack temp;
	// counter is initialized to 0
	// this is both the number of values in the stack as well as the next available index


	cout << temp.Size() << endl; // displays 0

	temp.Push(5);  // stores  5 into the array data at index 0 (counter) , counter is incremented to 1 

	temp.Push(34); // stores 34 into the array data at index 1 (counter) , counter is incremented to 2 

	temp.Push(22); // stores 22 into the array data at index 2 (counter) , counter is incremented to 3 



	cout << temp.Size() << endl; // displays 3



	cout << temp.Top() << endl ; // displays 22 the top value on the stack 

	temp.Pop();  // decrements counter to 2


	temp.Push(88); // stores 88 into the array data at index 2 (counter) , counter is incremented to 3 



	cout << temp.Top() << endl ; // displays 88 the top value on the stack 




	temp.Pop();  // decrements counter to 2

	cout << temp.Top() << endl ; // displays 34 the top value on the stack 


	temp.Pop();  // decrements counter to 1

	cout << temp.Top() << endl ; // displays 5  the top value on the stack 

}






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Macros
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File: main2.cpp 


#include "cmpslib19.h"


// include the standard template library stack
#include <stack>
#include "fraction.h"


// MACRO 
// a macro is basically kinda like search and replace
// we have used __LINE__ and __PRETTY_FUNCTION before, these are provided by the compler
// __LINE__ is replaced by the actual line number of code

// you can define your own macros
#define Player_Lives 3

// anywhere we put Player_Lives in our code the compiler will replace it with 3 before it compiles your code


// we can also wrap a define in logic.. this will set ELEMTYPE if it has not already been set
#ifndef ELEMTYPE  
#define ELEMTYPE  int
#endif


// if you comment out this line the line with " x contains the value"  will be skipped
#define DEBUG 1



int main()
{
 ELEMTYPE temp;// temp will be of type int
 cout << "temp is of type " << GetClassName(temp) << endl;

 cout << "Player_Lives: " << Player_Lives << endl;


#ifdef DEBUG 
  cout << "if DEBUG is defined to any value this will show "  << endl;
#endif



	return 0;
}








if we compile like normal 

g++ -Wall  -o runme2 main2.cpp    
./runme2 
temp is of type int
Player_Lives: 3
if DEBUG is defined to any value this will show 

temp is of type int the default for ELEMTYPE 


but we can pass in a value when we compile it will use that
to do this we use the -D flag 

g++ -Wall  -o runme3 -D ELEMTYPE=CFraction  main2.cpp    
./runme3 
temp is of type CFraction
Player_Lives: 3
if DEBUG is defined to any value this will show 

NOTICE that temp is now CFraction instead of int



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