AVRFreaks.net

 PORTx+=1;

//Atmega8, 8 MHz
#include <avr/io.h>
#include <avr/interrupt.h>     

ISR(TIMER0_OVF_vect)        //ovf 8 ms
{
static uint8_t state;       

   //if pinb.0=0 in 8 subsequent interrupts
   //then toggle portb.1
   if(bit_is_clear(PINB,0)) //if buton pressed
   {
      state++;
      if(state == 8) PORTB ^= (1<<1); //toggle Led
   }       
   else state = 0;
}

//===============================================================================
int main(void)
{
   DDRB   = 0b00000010; //portb.1 Led
   PORTB  = 0b00000001; //portb.0 buton, pull-up
   TCCR0  = (1<<CS02);  //prescaler 256
   TIMSK  = (1<<TOIE0); //enable timer0_ovf 
   sei();

   for(;;)
   {
   }
}

   DDRB |= 1<<PINB0;//assigning pin0 as output
   DDRB &= ~(1<<PINB1); //PINB1 as input
   DDRB |= 1<<PINB2;//assigning pin0 as output
   //Set the initial statuts of the both leds
   PORTB|=1<<PINB0;
   PORTB&=~(1<<PINB2);
   //This is a flag to keep the status
   int  pressed = 0;
   while(1)
   { 
          /*bit_clear is a simple routine to check whether a pin is high it is simple to write as a function or a macro*/
          if(bit_clear(PINB,1))
     {
          if(pressed ==0)
          {
          PORTB^=1<<PINB0;
           PORTB^=1<<PINB2;
          pressed = 1;
          }
     }
     else
     {
       pressed = 0;
     }
   }