From Arduino to Atmel Studio

#define F_CPU 16000000        // needed for delay.h

#include <avr/io.h>
#include <util/delay.h>       // needed for _delay_ms() function

void USART_Transmit( unsigned char data );
void USART_Init();
int main(void)
{
unsigned char count = 0;
   	
  /* setup() */	
  DDRB = 0x20;  // PB5 = Arduino pin 13	
  USART_Init(); // set up the USART for 115200 baud
  
  /* loop(); */
  while(1)
    {
	PORTB = PORTB ^ 0x20;  // toggle PORTB bit 5
	count ++;              // increment count
	if(count > 9)          // keep count < 10
	  count = 0;
	USART_Transmit( (count + 48) );  // convert count to ASCII and transmit it
	_delay_ms(500);		
    }
}

/* These functions are copied from the ATmega328P user Manual (20.5, 20.6.1) */

void USART_Init()
{
	/* Set baud rate */
	UBRR0H = 0;      
	UBRR0L = 16;     // UBRR0 = (F_CPU/( 8 * 115200 )) - 1 = 16.36
	/* set double speed mode */
	UCSR0A |= (1<<U2X0);
	/* Enable receiver and transmitter */
	UCSR0B = (1<<RXEN0)|(1<<TXEN0);
	/* Set frame format: 8data, 2stop bit */
	UCSR0C = (1<<USBS0)|(3<<UCSZ00);
}


void USART_Transmit( unsigned char data )
{
	/* Wait for empty transmit buffer */
	while ( !( UCSR0A & (1<<UDRE0)) );

	/* Put data into buffer, sends the data */
	UDR0 = data;
}