i am using avr atmega8 microcontroller....i am getting no idea how to read the value of a pin,I have used a IR sensor in that pin.

Don't you have documentation that gives you the info like this?

Since your question is about a hardware problem, I would ask it, in a hardware or embedded forum. Although I'd like to help, I am not familiar with that hardware.

I've mostly done work with AVR microcontrollers in Assembly, but I have a bit of experience with the C AVR syntax. Assuming you have the required header, you should be able to do the following:

// Sets "Data Direction register" for PORT A; 1 is output, 0 is input
// LSB of DDRA corresponds to pin 0; MSB of DDRA corresponds to pin 7
DDRA = 0b11111110;
// Set initial values for PORT A
PORTA = 0b00000001; // Set input as 1 to trigger pull-up resistor if needed

...

// Later, read the pin
if (bit_is_set(PINA,0))
{
   // Do something
}

This assumes your input is on pin 0 of PORT A. I used similar code for a tiny26 microcontroller. The syntax should be the same.

Thank u sir. Can you please tell me how to save a data from a pin in the memory of the microcontroller ?

the documentation is very necessary for you.
Here iam sharing a code i used on AVR atmega8, for 'Line Follower'
Your purpose must be different, but the complete code here may help you.

#define F_CPU 12000000UL // define cpu frequency for delay function
#include <avr/io.h> // includes input/output header file
#include <util/delay.h> // includes delay header file
/* Program for Line follower using Atmega8 microcontroller*/


//******************************************************************************
/* Connection of 3 PIN Sensor PORTs with atmega 8 in Mobi-botricks Kit

     PC4 Port is connected with PIN27 of Atmega 8
	 PC5 Port is connected with PIN28 of Atmega 8
	 PC3 Port is connected with PIN26 of Atmega 8(DTMF D3 is also sent to this pin)
	 PC2 Port is connected with PIN25 of Atmega 8(DTMF D2 is also sent to this pin)
	 PC1 Port is connected with PIN24 of Atmega 8(DTMF D1 is also sent to this pin)
	 PC0 Port is connected with PIN23 of Atmega 8(DTMF D0 is also sent to this pin)
	 PC6 Port is connected with PIN 1(Reset Pin) of Atmega 8
*******************************************************************************
	Connection of L293D IC  with atmega 8 in Mobi-botricks Kit

	Pin 2(A1) of L293D is Connected with PB2(Pin 16 of Atmega8)
	Pin 7(B1) of L293D is Connected with PB3(MOSI)(Pin 17 of Atmega8)
	**A1 and B1 are the input pins of Left side H-Bridge of L293D which is driving the Left Motor
	Pin 15 (A2) of L293D is Connected with PB0(Pin 14of Atmega8)
	Pin 10 (B2) of L293D is Connected with PB1(Pin 15 of Atmega8)

	Pin 1(EN1) and pin 9(EN2) is connected Via motor enable switch.
	when we switch on Enable Switch Both EN1 and EN2 are given
	5 Volt supply to enalbe both H-Bridges of L293D
	Pin 3 and pin6 of L293D is Connected with Left Motor Connector
	Pin 14 and Pin 11 of L293D is connected with Right Motor Connector */


//connect the left sensors on CN3 and right one on CN2




int main(void)
{
DDRB=0b11111111; //PORTB as output Port connected to motors
DDRC=0b0000000; //PORTC Input port connected to Sensors

int left_sensor=0, right_sensor=0;
while(1) // infinite loop
{
     left_sensor=PINC&0b0010000; // mask PC4 bit of Port C
     right_sensor=PINC&0b0100000;// mask PC5 bit of Port C


	 if((left_sensor==0b0000000) & (right_sensor==0b0000000)) //if both sensors "on"
              {
                 PORTB=0b00000000; // stop
                 left_sensor=0;
				 right_sensor=0;


               }

          if((left_sensor==0b0010000) & (right_sensor==0b0100000)) //if both sensors "on"
              {
                 PORTB=0b00001001; // move straight
                 left_sensor=0;
                 right_sensor=0;



               }
			if((left_sensor==0b0000000) & (right_sensor==0b0100000)) //if both sensors "on"
              {
                 PORTB=0b00000001; // turn left
                 left_sensor=0;
                 right_sensor=0;


               }
			 if((left_sensor==0b0010000) & (right_sensor==0b0000000)) //if both sensors "on"
              {
                 PORTB=0b00001000; // turn right
                 left_sensor=0;
                 right_sensor=0;


               }

 }
 }
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