[AVR] simulate Digital thermostat

#define F_CPU (12000000UL)
#include <avr/io.h>

#include <util/delay.h>
#include <stdlib.h>
#include <avr/interrupt.h>
void ADC_init(void);
unsigned int ADC_read(unsigned char);
int user_D_temp(void);
void seven_seg(unsigned int x);
int main(void)
{
    DDRB.2 = 1;//  is used for output resistor
	DDRB.0 = 0; // temperature increase switch
	DDRB.1 = 0; // temperature decrease switch
	DDRC = 0xFF;
	PORTC = 0x00; // 7 segment 1st and 2nd  digit
	DDRD=0xFF;
	PORTD=0x00;   // 7 segment	3rd digit				 
	
	ADC_init();
	
	unsigned int ADC_data;
	unsigned int i,temp_D;
	float t_duty,t1,t2,ADC_data1;
	while(1)
    {
		lcd_clear();
		ADC_data = ADC_read(0);
		ADC_data1=ADC_data/4;
		
		temp_D=user_D_temp();
		
		t_duty = (1-(((ADC_data1)-temp_D)/2));
		PORTB.2=1;
		t1=10*t_duty;
		
	
		for(i=0;i<t1;i++)
		_delay_ms(1000);
		PORTB.2=0;
		t2=10*(1-t_duty);
		
		for(i=0;i<t2;i++)
		_delay_ms(1000);  
        //TODO:: Please write your application code 
    }
}

void ADC_init(void) // Initialization of ADC
{
	ADMUX =(1<<REFS0); // internal 2.56v with external capacitor at AREF
	ADCSRA=(1<<ADEN)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0);
	// Enable ADC and set Prescaler division factor as 128`
}

unsigned int ADC_read(unsigned char ch)
{
	ch= ch & 0b00000111; // channel must be b/w 0 to 7
	ADMUX |= ch; // selecting channel
	
	ADCSRA|=(1<<ADSC); // start conversion
	while(!(ADCSRA & (1<<ADIF))); // waiting for ADIF, conversion complete
	ADCSRA|=(1<<ADIF); // clearing of ADIF, it is done by writing 1 to it
	
	return (ADC);
}

int user_D_temp(void)
{
	unsigned int temp=0;
	if(PORTB.0==1)
	{
		temp++;
		seven_seg(temp);
	}
	else if(PORTB.1==1)
	{
		temp--;
		seven_seg(temp);
	}
	else
		temp=temp;
	return(temp);
}

void seven_seg(unsigned int x)
{
   unsigned int y,z;
   y=x/100;	   //1st digit on lower nibble
   PORTC &=(0x0F)&y;
   y=x%100;
   z=y/10;	  //2nd digit on higher nibble
   PORTC |=(0xF0)|(z<<4);
   z=y%10;	  //3rd digit on lower nibble
   PORTD &=z;
}