read() in c raspberry pi gsm-module - c

Question

I am working on a project where i can send sms with my raspberry pi thats connected to a sim300s module thrue a usb to serial connection.
problem:
sim300 doesnt detect the simcard , harware malfunction, i have ordered a new one. Until then i want to check if the connection works between the 2.
Now i want to send at command and receive OK(or something like that) Here is my code:
the value that is stored in string buf is TATATATAT.... etc.. etc..
Can someone explain why i am not getting OK back? Am i doing something wrong?
#include <stdio.h> /* Standard input/output definitions */
#include <string.h> /* String function definitions */
#include <unistd.h> /* UNIX standard function definitions */
#include <fcntl.h> /* File control definitions */
#include <errno.h> /* Error number definitions */
#include <termios.h> /* POSIX terminal control definitions */
/*
* 'open_port()' - Open serial port 1.
*
* Returns the file descriptor on success or -1 on error.
*/
int main(int argc, char* argv[])
{
puts("start open_port");
open_port();
puts("open_port started ");
}
int
open_port(void)
{
char reply;//not shure if its gonna be used
struct termios options;
int n=0;
int fd; /* File descriptor for the port */
char buf[50];
int valueBytes;
int x = 0;
fd = open("/dev/ttyUSB0", O_RDWR | O_NOCTTY ); //| O_NDELAY);
if (fd == -1)
{//could not open port
fprintf(stderr, "open_port: Unable to open /dev/ - %s\n",
strerror(errno));
}
printf("%d",fd);
tcgetattr(fd, &options); //get current options for port
puts("test1");
cfsetispeed(&options, B9600);//set baud rate
cfsetospeed(&options, B9600);//set baud rate
puts("\n2");
options.c_cflag |= (CLOCAL | CREAD | CRTSCTS);//enable the receiver and set local mode
puts("\n3");
options.c_cflag &= ~PARENB;//disable parity generation and detection
options.c_cflag &= ~CSTOPB;//Use one stop bit per character
options.c_cflag &= ~CSIZE;
options.c_cflag |= CS8;//use 8 bits to send or receive characters
options.c_lflag &= ~(ICANON | /* Enable canonical input (else raw) */
ECHO | /*Enable echoing of input characters */
ECHOE | /*Echo erase character as BS-SP-BS*/
ISIG); /*Enable SIGINTR, SIGSUSP, SIGDSUSP, and SIGQUIT signals*/
tcsetattr(fd, TCSANOW, &options);//TCSANOW change values immediately
puts("4");
n = write(fd, "AT\r", 4); // n = write(fd, "AT+CMGF=1\r", 10);
if (n < 0){
puts("write() of 4 bytes failed!");}
if(read(fd, buf, 2) < 0){
puts("it doesnt work"); }
fcntl(fd, F_SETFL, FNDELAY);
valueBytes=read(fd, buf,50);
printf("%d",valueBytes);
if(valueBytes < 0){
printf(strerror(errno));}
puts("6.3");
for(x; x<50;x++){
printf("%c",buf[x]);
}
close(fd);
puts("7");
return (fd);
puts("8");
}