Calculator Project with just keypad and LCD 8051

/* calculator Project for 8051---
   Possible Operation- add, sub, mul, div
   limitations- decimal part is truncated
                result upto only 6decimals */
/* algorithm::
     step1:store the entered values in an array
         if any operator key is pressed goto step2
  step2:store the var1 here (using convertArrayToDecimal() function)
        and also store the operator pressed
         if '=' operator is pressed goto step3
  step3:do the respective operation and display the result */

#include<reg51.h>
#include"lcd_display.h"

int pow(int, int);
void convertArrayToDecimal(int*);
void clear_array();
void column1();
void column2();
void column3();
void column4();
char getkey();

sbit c1=P2^0;
sbit c2=P2^1;
sbit c3=P2^2;
sbit c4=P2^3;
sbit r1=P2^4;
sbit r2=P2^5;
sbit r3=P2^6;
sbit r4=P2^7;


int var1=0,var2=0,dummy_var,row,col;

char values[4][4]={{55,56,57,'/'},
                   {52,53,54,'*'},
          {49,50,51,'-'},
          {' ',48,'=','+'}};

int num[5]; // to store the entered keys
int i=0;
void main()
{
char key;
unsigned char operation;
int var_count=0;
int result;

  
  r1=r2=r3=r4=rs=en=0;
  c1=c2=c3=c4=1;

  P3=0x00;
  TMOD=0x01;
  
  while(1)
  {
    
     while(c1==1 && c2==1 && c3==1 && c4==1);  
  key=getkey();
  
  if(key==' ')
  {
    lcd_init();
    var1=0;
    var2=0;
    clear_array();
  }

  if(key!='/' && key!='+' && key!='-' && key!='*' && key!=' ' && key!='=')
  {
  num[i]=key-48;
  lcd_data(key);
  i=i+1;
  }

  if(key=='/' || key=='+' || key=='-' || key=='*' )
  {      
            dummy_var=0;
     convertArrayToDecimal(num);
     var1=dummy_var;
     operation=key;
     lcd_data(key);
  }

  if(key=='=')
  {
     dummy_var=0;
     convertArrayToDecimal(num);
     var2=dummy_var;
     lcd_cmd(0xc0);
     lcd_dataS("result is-");
   switch(operation)
    {
     case '+': result=var1+var2;
               lcd_dataint(result);
        break;
     case '-': result=var1-var2;
               lcd_dataint(result);
        break;
     case '*': result=var1*var2;
               lcd_dataint(result);
        break;
     case '/': result=var1/var2;
               lcd_dataint(result);
        break;
    }
  }
  }          //end of while
}

char getkey()
{
       if(c1==0)
    {
      column1();
      while(!c1);
     row=0;
    }
       if(c2==0)
    {
      column2();
      while(!c2);
          row=1;
    }
       if(c3==0)
    {
         column3();
      while(!c3);
         row=2;
    }
    if(c4==0)
    {
         column4();
      while(!c4);
         row=3;
    }  
      
   return values[col][row];
}

void convertArrayToDecimal(int *p)
{
  int k=i-1;
   while(i>0)
    {
      dummy_var=dummy_var+((*p) * pow(10,k));
      k--;
   i--;
   p++;
 }
}

int pow(int x, int z)
{
 int value=1;

   while(z>0)
    {
      value=value*x;
      z=z-1;
    }
 return value;
}

void clear_array()
{
 int j;
 for(j=0;j<5;j++)
  num[j]='\0';
}
 
void column1()
{

 r1=r2=r3=r4=1;

 r1=0;
 if(c1==0)
 col=0;

 r1=1;r2=0;
 if(c1==0)
 col=1;

 r1=1;r2=1;r3=0;
 if(c1==0)
 col=2;

 r1=1;r2=1;r3=1;r4=0;
 if(c1==0)
 col=3;
 
 r1=r2=r3=r4=0;
 
}


void column2()
{

 r1=r2=r3=r4=1;

 r1=0;
 if(c2==0)
 col=0;

 r1=1;r2=0;
 if(c2==0)
 col=1;

 r1=1;r2=1;r3=0;
 if(c2==0)
 col=2;

 r1=1;r2=1;r3=1;r4=0;
 if(c2==0)
 col=3;
 
 r1=r2=r3=r4=0;
 
}


void column3()
{

 r1=r2=r3=r4=1;

 r1=0;
 if(c3==0)
 col=0;

 r1=1;r2=0;
 if(c3==0)
 col=1;

 r1=1;r2=1;r3=0;
 if(c3==0)
 col=2;

 r1=1;r2=1;r3=1;r4=0;
 if(c3==0)
 col=3;
 
 r1=r2=r3=r4=0;

}

void column4()
{

 r1=r2=r3=r4=1;

 r1=0;
 if(c4==0)
 col=0;

 r1=1;r2=0;
 if(c4==0)
 col=1;

 r1=1;r2=1;r3=0;
 if(c4==0)
 col=2;

 r1=1;r2=1;r3=1;r4=0;
 if(c4==0)
 col=3;
 
 r1=r2=r3=r4=0;

}