PIC16F877 matrix keyboard

//The program does not perform key debounce, nor does it consider the situation where multiple keys are pressed at the same time.
//The lowest two digital tubes display the corresponding keys (e.g., if S10 is pressed, 10 is displayed; if S25 is pressed, 25 is displayed)
//FF is displayed when no key is pressed 
//The key and key scanning results satisfy the following relationship:
// Key Scan Result (result) Key Scan Result  
// K10 0XE7 K18 0XB7
// K11 0XEB K19 0XBB
// K12 0XED K20 0XBD
// K13 0XEE K21 0XBE
// K14 0XD7 K22 0X77
// K15 0XDB K23 0X7B
// K16 0XDD K24 0X7D
// K17 0XDE K25 0X7E

//Hardware requirements: All DIP switches S4 are set to ON
// All DIP switches S6 are set to ON, DIP switch S5 positions 5-6 are ON, and other positions are OFF
// Other DIP switches are set to OFF

#include //Includes the predefined
 __CONFIG(0x1832) internal resources of the MCU;        
//Chip configuration word, watchdog off, power-on delay on, power-off detection off, low voltage programming off, encryption, 4M crystal HS oscillation

 int result;
 void delay(); //delay function declaration
 void init(); //I/O port initialization function declaration
 void scan(); //Key scanning program declaration
 void display(int x); //Display function declaration
//---------------------------------------------------
                             //Main program  
void main()
{
  while(1) //Loop work
    {
      init(); //Call initialization subroutine
      scan(); //Call key scanning subroutine
      display(result); //Call result display subroutine
    }
 }
 
//---------------------------------------------------
//Initialization function
void init() 
 {
  ADCON1=0X07; //Set port A as a normal I/O port
  TRISA=0X0f; //Set the high 2 bits of port A as output and the low 4 bits as input
  TRISC=0XF0; //Set the high 4 bits of port C as input and the low 4 bits as output
  TRISD=0X00; //Set port D as output PORTA
  =0XFF;              
  PORTD=0XFF; //Clear all displays first
 }

//---------------------------------------------------
//Key scanning program
void scan()
{
 PORTC=0XF7; //C3 outputs low level, and the other three bits output high level
 asm("nop"); //Insert a certain delay to ensure that the level is stable
 result=PORTC; //Read back the high 4 bits of port C
 result=result&0xf0; //Clear the low 4 bits
 if(result!=0xf0) //Judge whether the high 4 bits are all 1 (all 1 means no button is pressed)?
   {
     result=result|0x07; //No, add the lower 4 bits 0x07 as the result of the key scan
   }
 else //Yes, change the lower 4 bits output and re-judge whether a key is pressed
   {
   PORTC=0XFb; //C2 outputs low level, and the other three bits output high levelasm
   ("nop"); //Insert a certain delay to ensure that the level is stableresult
   =PORTC; //Read back the high 4 bits of port
   Cresult=result&0xf0; //Clear the low 4 bitsif
   (result!=0xf0) //Judge whether the high 4 bits are all 1 (all 1 means no key is pressed)
     {
     result=result|0x0b; //No, add the lower 4 bits 0xb as the result of the key scan
     }
   else //Yes, change the lower 4 bits output and re-scan
       {
       PORTC=0XFd; //C1 outputs low level, and the other three bits output high levelasm
       ("nop"); //Insert a certain delay to ensure that the level is stableresult
       =PORTC; //Read back the high 4 bits of port C
       result=result&0xf0; //Clear the low 4 bitsif
       (result!=0xf0) //Judge whether the high 4 bits are all 1 (all 1 means no button is pressed)
        {
        result=result|0x0d; //No, add the low 4 bits 0x0d as the result of the key scan
        }
       else //Yes, change the output of the low 4 bits and rescan
          {
          PORTC=0XFe; //C0 outputs low level, and the other three bits output high levelasm
          ("nop"); //Insert a certain delay to ensure that the level is stableresult
          =PORTC; //Read back the high 4 bits of port C
          result=result&0xf0;//Clear the low 4 bitsif
          (result!=0xf0) //Judge whether the high 4 bits are all 1 (all 1 means no button is pressed)
            {
             result=result|0x0e;//No, add the low 4 bits 0x0e as the result of the key scan
            }
          else //Yes, all key scans are completed, no key is pressed, set the no key pressed flag
            {
             result=0xff; //The scan result is 0xff, which is used as a sign that no key is pressed
            }   
          }      
      }
   }
 }

//------------------------------------------------ ----------
//Display program
void display(int x)
  {
   switch(result)                 
      {
       case 0xe7:
                 PORTD=0xf9;PORTA=0X2F;delay();PORTD=0xc0;PORTA=0X1F;delay ();break; //K10
       case 0xeb:
                 PORTD=0xf9;PORTA=0X2F;delay();PORTD=0xf9;PORTA=0X1F;delay();break; //K11
       case 0xed:
                 PORTD=0xf9;PORTA=0X2F ;delay();PORTD=0xa4;PORTA=0X1F;delay();break; //K12
       case 0xee:
                 PORTD=0xf9;PORTA=0X2F;delay();PORTD=0xb0;PORTA=0X1F;delay();break ; //K13
       case 0xd7:
                 PORTD=0xf9;PORTA=0X2F;delay();PORTD=0x99;PORTA=0X1F;delay();break; //K14
       case 0xdb:
                 PORTD=0xf9;PORTA=0X2F;delay();PORTD=0x92;PORTA= 0X1F;delay();break; //K15
       case 0xdd:
                 PORTD=0xf9;PORTA=0X2F;delay();PORTD=0X82;PORTA=0X1F;delay();break; //K16
       case 0xde:
                 PORTD=0xf9; PORTA=0X2F;delay();PORTD=0XF8;PORTA=0X1F;delay();break; //K17
       case 0xb7:
                 PORTD=0xf9;PORTA=0X2F;delay();PORTD=0X80;PORTA=0X1F;delay();break; //K18
       case 0xbb:
                 PORTD=0xf9;PORTA=0X2F;delay();PORTD=0X90;PORTA= 0X1F;delay();break; //K19
       case 0xbd:
                 PORTD=0xa4;PORTA=0X2F;delay();PORTD=0xc0;PORTA=0X1F;delay();break; //K20
       case 0xbe:
                 PORTD=0xa4; PORTA=0X2F;delay();PORTD=0xf9;PORTA=0X1F;delay();break; //K21
       case 0x77:
                 PORTD=0xa4;PORTA=0X2F;delay();PORTD=0xa4;PORTA=0X1F;delay();break; //K22
       case 0x7b:
                 PORTD=0xa4;PORTA=0X2F;delay();PORTD=0xb0;PORTA= 0X1F;delay();break; //K23
       case 0x7d:
                 PORTD=0xa4;PORTA=0X2F;delay();PORTD=0x99;PORTA=0X1F;delay();break; //K24
       case 0x7e:
                 PORTD=0xa4; PORTA=0X2F;delay();PORTD=0x92;PORTA=0X1F;delay();break; //K25
       case 0xff:
                 PORTD=0x8e;PORTA=0X2F;delay(); PORTD=0x8e; PORTA=0X1F; delay(); //No button pressed
      }
   }

//------------------------------------------------------------------
//Delay program
void delay() //Delay program
    {
     int i; //Define integer variables
     for(i=0x100;i--;); //Delay
    }