AVR USART communication - c

Question

I am implementing USART communication on an AVR micro-controller. Below is my code. At the moment, I can send a character, send a string and receive a character. I have a method to receive a string.
The method is called char* receive_string() and returns the address of the string that I am receiving. This is the 55 element char array to hold the string, char string[55]. However, for example, when I send the word hello to the micro-controller, this method returns only the first character h. What is it that I am doing wrong?
#include <avr/io.h>
#include <util/delay.h>
#include <string.h>
#include <avr/interrupt.h>
// macro definition
#define bit(n) (1 << n) // bit
#define sbit(v, n) v |= (1 << n) // set bit
#define cbit(v, n) v &= !(1 << n) // clear bit
#ifndef F_CPU
#define F_CPU 16000000
#endif
#define BAUD 9600 // baud rate
#define M_UBRR ((F_CPU/16/BAUD)-1) //contents of UBRRnH and UBRRnL registers
// function prototypes
void usart_init();
void send_char(char);
void send_string(char*);
char receive_char();
char* receive_string();
char string[55];
int main() {
usart_init();
char* msg = receive_string();
sei();
while (1) {
send_string(msg);
_delay_ms(1000);
}
return 0;
}
void usart_init() {
UBRR0H = (M_UBRR >> 8); // setting baud rate
UBRR0L = M_UBRR;
UCSR0B = (1 << TXEN0) | (1 << RXEN0) | (1 << RXCIE0); // enable transmitter and receiver
UCSR0C = (1 << USBS0); // 2 stop bit
UCSR0C = (1 << UCSZ00) | (1 << UCSZ01);
}
void send_char(char byte) {
while (!(UCSR0A & (1 << UDRE0))); // wait until the register is empty
UDR0 = byte; // put a char in the UDR0 register
}
void send_string(char* string) {
int i;
int len = strlen(string);
for (i = 0; i < len; i++) {
send_char(string[i]);
}
}
char receive_char() {
while (!(UCSR0A & (1 << RXC0))); // wait until all data in receive buffer is read
return UDR0;
}
char* receive_string() {
char x;
int len = strlen(string);
int i = 0;
while (i < len) {
x = receive_char();
string[i++] = x;
}
string[len] = '\0';
return (string);
}

Answer 1

strlen(string) in your code does not make sense. How can you get the length of a string that has not been sent yet?
Change that to len = 55 or len = sizeof(string).
In C, strlen counts the number of characters before finding the zero terminator.