[AVR] problem about communication with sim900a through atmega16

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include <uart_lib.h>
#include <stdio.h>



static unsigned char c;

static char line=0, status = 0,index = 0,mob[10] = "          ", A[20]="asdfghjk";
ISR(USART_RXC_vect)
{
	c = UDR;
	if(index<16)
A[index]=c;
	index++;
	if (c==0x0A)
{
status|=1;
index = 0;
line=0;
}

	else if(index == 5)
{
			 if((strncmp(A,"+CMTI",5) == 0))
{
 status|=4;
line=1;
}
		else if((strncmp(A,"+CLIP",5) == 0))
{
 status|=2;
line=1;
}
		else if((strncmp(A,"NO CA",5) == 0))
{
 status&=~2;
line=1;
}
	}
	else if(index>11&index<22&(status>>1))mob[index-12]=c;
}




int main(void) {
	DDRA|=(1<<0);
	set_uartbaud(9600);
	enable_uart_rxcint();
	
	sei();
	_delay_ms(2000);
	sendstring_uart("AT\r");
	sendstring_uart("at+clip=1\r");
	_delay_ms(2000);
	while (1)
 {
		if(status==3)
{
			_delay_ms(100);
		if(status>>1&(strncmp(mob,"9694324852",10) == 0))
{
			sendstring_uart("ath\r");
			PORTA^=(1<<0);
			status=1;
		}
	
		}

		
	}
}

#include<uart_lib.h>
#include<avr/io.h>
#include<util/delay.h>
#define FOSC 4000000
void set_uartbaud(int BAUD)
{
	UBRRH = (unsigned char)((FOSC/16/BAUD-1)>>8);
	UBRRL = (unsigned char)(FOSC/16/BAUD-1);
	UCSRC|=(1<<URSEL)|(1<<UCSZ1)|(1<<UCSZ0);
	UCSRB|=(1<<RXEN)|(1<<TXEN);
}

void disable_uart()
{
	UCSRB&=~(1<<TXEN);
	UCSRB&=~(1<<RXEN);
}



void enable_uart_txcint()
{
	UCSRB|=(1<<TXCIE);
}

void enable_uart_rxcint()
{
	UCSRB|=(1<<RXCIE);
}

void enable_uart_udreint()
{
	UCSRB|=(1<<UDRIE);
}

void disable_uart_txcint()
{
	UCSRB&=~(1<<TXCIE);
}

void disable_uart_rxcint()
{
	UCSRB&=~(1<<RXCIE);
}

void disable_uart_udreint()
{
	UCSRB&=~(1<<UDRIE);
}

void sendchar_uart(char data)
{
	int temp;
	temp=UCSRA&(1<<UDRE);
	temp=temp>>UDRE;
	while(!temp)
	{

	}
	UDR=data;
}

char getchar_uart()
{
	// Wait until a byte has been received

	while((UCSRA&(1<<RXC)) == 0);

	// Return received data

	return UDR;

}

void sendstring_uart(char v[])
{
	int i;
	for(i=0;i<strlen(v);i++)
	{
		sendchar_uart(v[i]);
		_delay_ms(10);
	}
}

#include <avr/io.h>

#define FOSC 4000000// Clock Speed