Waveform generator & DA conversion based on 51 single chip microcomputer (dac0832)

#include"reg51.h"
#define uchar unsigned char
sbit ksaw=P2^0; //Sawtooth wave button.
sbit ktran=P2^1; //Triangle wave button.
sbit ksquare=P2^2; //Square wave button.
sbit ksin=P2^3; //Sine wave button.

uchar key1;
uchar keya;
uchar keyb;
uchar keyc;
uchar keyd;void delay( );
uchar code tab[128]={
64,67,70,73,76,79,82,85,88,91,94, 96,99,102,104,106,
109,111,113,115,117,118,120,121,123,124,125,126,126,
127,127,127,127,127,127,127,126,126,125,124,123,12 1,
120,118,117,115,113,111,109,106,104,102,99,96,94,91,
88,85,82,79,76,73,70,67,64,60,57,54,51,48,45,42,39,
36,33,31, 28,25,23,21,18,16,14,12,10,9,7,6,4,3,2,1,
1,0,0,0,0,0,0,0,1, 1,2,3,4,6,7,9,10,12,14,16,18,21,23,
25,28,31,33,36,39,42,45,48,51,54,57,60};

void delay( )
{
  uchar i;
  for(i=0;i<255;i++);
}
void saw(void) //sawtooth wave.
{
 uchar i;
 while(1)
 {
  if(keya==1)
  {
  for (i=0;i<255;i++)
  P0=i;
   }
   else break;
  }
 }
void tran(void) //Triangular wave
{
 uchar i;
 while(1)
 {
  if(keyb==1)
  {
  for(i= 0;i<255;i++)
  P0=i;
  for(i=255;i>0;i--)
  P0=i;
  }
  else break;
  }
}
void square(void) //square wave
{
  while(1)
  {
   if(keyc==1)
   {
   P0=0x00;
   delay();
   P0=0xff;
   delay();
    }
 else break;
  }

}

void sin( ) //sine wave
{
  unsigned int i=0;
  while(1)
  {
   if(keyd==1)
   {
   if(++i==128)i=0;
       {P0=tab[i];}
    }
 else break;
  }
}
void main(void) //main function
{
  EA=1;
  EX0=1;
  while(1)
  {
  if(key1)
  {
   switch(key1)
   {
    case 0x01:
    //P0=0XC0;//
    saw();
    break;
  case 0x02:
    //P0=0XC0;//
    tran();
    break;
     case 0x03:
    //P0=0XBE;//
    square();
    break;
  case 0x04:
    //P0=0XB6;/ /
    sin();
    break;
   }
 }
  }

}

void int0(void)interrupt 0 using 1
{
if(ksaw==0)
   {key1=0x01;keya=1;keyb=0;keyc=0;keyd=0;}                 
 if(ktran==0)
  {key1=0x02 ;keya=0;keyb=1;keyc=0;keyd=0;}
  if(ksquare==0)
  { key1=0x03;keya=0;keyb=0;keyc=1;keyd=0;}
 if(ksin ==0)
  {key1=0x04;keya=0;keyb=0;keyc=0;keyd=1;}
}

The pictures are as follows: