How to write program

I am trying to write keypad program, I work with 8051 and keil compiler so I did google search and I found so many links . I have read following three links but still I am confuse because the program has been written differently in all the three links and I don't understand how to write proficient program for keypad interfacing.

https://electrosome.com/interfacing-keypad-8051-microcontroller-keil-c/
https://www.pantechsolutions.net/mi...-interface-keypad-with-8051-development-board
https://circuitdigest.com/microcontroller-projects/keypad-interfacing-with-8051-microcontroller

I don't want to just copy paste the program.I want to write program by proper understanding. I have seen the keypad datasheet and I understand the basic logic but I don't understand how to start to writing program.

Can anyone guide me to write program. If i make program into small parts then which one part's should I make first and then later.

 

Many many thanks for helping me I understand the loops, while loops, if else statements but the problem is that when I am trying to write program I am facing problems.

If 8 pins of matrix keypad connected to port P2 of 8051
Now I know how does matrix keypad connected to 8051.I don't know how to mention in program that 8 pins of matrix keypad connected to port P2 of 8051 What we do, we just define the port

Code:

#include<reg51.h>
#define keyport P2      

do we write like this

Code:

#include<reg51.h >   //Header file for 8051
#define column P2_0     //column 1
#define column P2_1     //column 2
#define column P2_2     //column 3
#define column P2_3     //column 4
#define row P2_4     //row 1
#define row P2_5     //row 2
#define row P2_6     //row 3
#define row P2_6     //row 4

do we set row and column like this

Code:

//Keypad Connections
#include<reg51.h >   //Header file for 8051
sbit column1 = P2^0;
sbit column2 = P2^1;
sbit column3 = P2^2;
sbit column4 = P2^3;
sbit row1 = P2^4;
sbit row2 = P2^5;
sbit row3 = P2^6;
sbit row4 = P2^7;

I am explaining handy program for the switch debouncing

Code:

/* Debounce time */
void Debounce(unsigned int i)
{
  for (i =0; i < 2000; i++);
  {
 
  }
}
   if(switch == 0)  
     {
        // wait 20 ms time  //
        Debounce(20);            
 
         // check switch again //
           if(Switch == 0)
 
            {
 
              }

This is my best attempt to start writing program. I am so confuse because of different type of explanations. I really don't know what to do, I hope you will point out me in right direction

 

I am only familiar with 8051 and arm cortex m0 micro-controller. If possible can you help me to make common program for keypad interfacing like handy program