need help for gsm programming!!!

the 1st do while loop is working properly but the program run till receive the data from modem ofprintf("at+cgmm\r"); then the program stops working ....

any solution on it?

#include <htc.h>
#include <stdio.h>
#include "usart.h"
#include "delay.h"
#include <string.h>

int main(void)
{
//Initialize PORTD
//PD0 as Output
TRISB=0b00000000;
TRISC=0b10000000;
INTCON=0; // purpose of disabling the interrupts.
init_comms(); // set up the USART - settings defined in usart.h

char input[80],i;




PORTB =0B11111111; //PORTB0 = HIGH
DelayMs(1000);
PORTB =0B00000000; //PORTB0 = LOW
DelayMs(500);
while(1)
{
printf("at\r");
do
{
gets(input);
i=strstr(input,"OK"); // Find OK from input
} while(i!=input);
RB0=1;
DelayMs(1000);
RB0=0;
DelayMs(500);
printf("at+cgmm\r");
do
{
gets(input);
i=strstr(input,"OK"); // Find OK from input
} while(i!=input);
RB1=1;
DelayMs(1000);
RB1=0;
DelayMs(500);




}

}