Program checking PINs level, send it and port name via uart (str[] = {port_name, pin_number})
But when sending a string has length equal 3.
Why and atfter what changing str[2] -> str[3], if string length initialize like str[2] and in code not add values more then 2?

#include "globals.h"
#include "variables.h"

#include "ports.h"
#include "uart.h"
#include "pin_macros.h"

#include "setup.h"

extern volatile uint8_t pinNumber;

extern volatile uint8_t port_value;

extern char str[2];
extern char previouse_str[2];

extern uint8_t trigger_D;

void initialization ()
{
    WDT_off();
    
    PORTS_setup();
    
    ACD_setup();
    ADC_setup();

    interruptsInit();
    
    USART_Init(MYUBRR);

    if (!ACTIVE(D10))
    {
        str[0] = PORT_NAME_B; //0x42
        str[1] = (char) (BITNUM(D10) + 7); 
        
        USART_send_str(str); // *1 
    }
}

int main(void)
{
    initialization();
    
    while(1){}
}

ISR (PCINT2_vect)
{
    _delay_ms(20);
    
    uint8_t count = 0;
    
    str[0] = PORT_NAME_D;
    str[1] = (char) 0;

    port_value = ~(PIND >> 2);

    if ((PIND >> 2) != ALL_PINS_HIGH)
    {
        pinNumber = 0;
        
        if ((PIND >> 2) == ALL_PINS_HIGH)
        {
            count = 0;
        } else {
            count = 1;
        } //end IF
    
        port_value &= (~((1<<6) | (1<<7)));
    
        while (port_value)
        {
            if (port_value != 1)
            {
                ++count;
            } //end IF
        
            port_value = port_value >> 1;
        } //end while
    
        ++count;
    
        pinNumber = count;
    } //end IF
    
    str[1] = (char) pinNumber;

    if (!((PIND >> 2) == ALL_PINS_HIGH))
    {
        if (str[1] != previouse_str[1])
        {
            if (trigger_D == 1)
            {
                //trigger_D = 0;
                USART_send_str(str);     //*2
                
            } else {
                
                trigger_D = 1;
                
            } //end IF
        } //end IF
    } else {
        
        trigger_D = 1;
        str[1] = 0;
        USART_send_bit(str[0]);
        
    } //end IF
    
    strcpy(previouse_str, str);
}

ISR (PCINT0_vect)
{
    uint8_t count = 7;
    
    str[0] = PORT_NAME_B;
    str[1] = (char) 0;
    
    _delay_ms(20);

    port_value = ~PINB & (~((1<<6) | (1<<7)));

    if ((PINB >> 2) != ALL_PINS_HIGH)
    {
        pinNumber = 0;
        
        while (port_value)
        {
            if (port_value != 1)
            {
                ++count;
            } //end IF
            
            port_value = port_value >> 1;
        } //end while
        
        ++count;
        
        pinNumber = count;
    } //end IF
        
    str[1] = (char) pinNumber;
    
    if (!((PINB) == ALL_PINS_HIGH))
    {
        if (str[1] != previouse_str[1])
        {
            trigger_D = 0;
            
            USART_send_str(str);
        }
    } else {
        str[1] = 0;
        USART_send_bit(str[0]);
    } //end IF
    
    strcpy(previouse_str, str);
}

1. send -> 0x42 0x09 0x01, if variable trigger_D change to ‘0’ -> 0x42 0x09 and strlen(str) equal 2.
2. in this send string for ping D2 equal “0x44 0x02 0x01”, if change trigger_D to 0 before sending, string will be have length equal 2.