Atmega328P constantly restarting when defining a function

I wanted to make a simple led on/off program using USART interface. When the code doesn't have any functions other than main it runs fine, however Arduino keeps resetting when one is included. At this point I have no clue what could I be doing wrong. Here's the code:

#include <avr/io.h>
#include <util/delay.h>

#define BAUD 19200
#define BAUDRATE ((F_CPU / 16 / BAUD) - 1)

// void init()
// {
//     // Keeps resetting when uncommented, runs fine when commented
// }

int main() {
    // Initialize USART
    UBRR0H = (BAUDRATE >> 8);
    UBRR0L = BAUDRATE;
    UCSR0B = (1 << RXEN0);
    UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);
    // Set bit 3 to output and pull it high
    DDRD |= 0b00001000;
    PORTD = 0b00001000;

    char char_arr[128];

    while(1)
    {
        int i;
        // Read USART
        for(i = 0; i < 128; i++){
            loop_until_bit_is_set(UCSR0A, RXC0);
            char c = UDR0;
            if(c == '\r')
                break;
            char_arr[i] = c;
        }
        // Handle received characters
        for(int j = 0; j < i; j++){
            switch(char_arr[j]){
                case '1': 
                    PORTD = 0b00001000; 
                    break;
                case '0': 
                    PORTD = 0b00000000; 
                    break;
            }
            _delay_ms(100);
        }
    }
}