7 segment multiplexing problem in pic using microc

unsigned int count;
short int ds1,ds2,ds3,ds4,i;

short int mask(short int get)
{
switch (get)
{
 case 0: return 0xc0;
 case 1: return 0xf9;
 case 2: return 0xa4;
 case 3: return 0xb0;
 case 4: return 0x99;
 case 5: return 0x92;
 case 6: return 0x82;
 case 7: return 0xf8;
 case 8: return 0x80;
 case 9: return 0x98;
 }
}

void interrupt()
{

if(rb0_bit)
{

intcon.intf=0;
delay_ms(10);
count++;
if(count>9999) count=0;
}
}

void main()
{
cmcon=0x07;
adcon1=0x06;
option_reg.intedg=1;
INTCON.GIE = 1;
INTCON.INTE = 1;
 trisd=0x00;
 trisb=0x01;
 trisc=0x10;
 portc=0xff;
 portd=0xff;
 count=1234;
 do
 {
  ds1=(count%10);
  ds1= mask(ds1);
  ds2=(count/10)%10;
  ds2= mask(ds2);
  ds3=(count/100)%10;
  ds3= mask(ds3);
  ds4=(count/1000);
  ds4= mask(ds4);

  for(i=0;i<50;i++)
  {
   portd=(ds4);
   portc.f0=0;
   portc.f1=1;
   portc.f2=1;
   portc.f3=1;
   delay_ms(1);
   portd=(ds3);
   portc.f0=1;
   portc.f1=0;
   portc.f2=1;
   portc.f3=1;
   delay_ms(1);
   portd=(ds2);
   portc.f0=1;
   portc.f1=1;
   portc.f2=0;
   portc.f3=1;
   delay_ms(1);
   portd=(ds1);
   portc.f0=1;
   portc.f1=1;
   portc.f2=1;
   portc.f3=0;
   delay_ms(1);
  }
 }while(1);
}