How to set apn in sim900 using keil code

Hello friends..
I have learn sim900 module connect the gprs mode and get the HTTP data for any site or we can say url..
so
i try this below code in keil,But the apn was not set,so got he error,,
so how to solve ...ples Tell me..


int main (void)
{
unsigned char t=1,z;
// int j;

IO0DIR = 0xFFFFFFFF;
init_lcd();
uart0_init();
lcd_clear();
delay(100000);

while(z)
{
i=0;
t=1;
while(t)
{
if(i==9)
{
i=0;
}
uart0_puts("AT\r");
while(i<9);
delay(1000);
if(a[5] == 'O' && a[6] == 'K')
{
lcd_clear();
lcd_putstring(0,"GSM Init OK");
t=0;

}
else
{
lcd_clear();
lcd_putstring(0,"GSM Init Error");
delay(10000);
i=0;
delay(1000);
}
t=0;
}

delay(10000);
i=0;
t=1;
while(t)
{
if(i==16)
{
i=0;
}
uart0_puts("AT+CGATT=1\r");
while(i<16);
lcd_clear();
delay(100000);
if(a[13] == 'O' && a[14] == 'K')
{
lcd_clear();
lcd_putstring(0,"GPRS ACTIVE");

t=0;
//i=0;
}
else
{
lcd_clear();
lcd_putstring(0,"GPRS FAILED");
delay(10000);
i=0;
//delay(100000);
t=0;
}
}
delay(10000);
t=1;
i=0;
while(t)
{
if(i==25)
{
i=0;
}
delay(100000);
uart0_puts("AT+CSTT=\"www\"\r");
while(i<25);
delay(100000);
lcd_clear();

lcd_putchar(a[0]);lcd_putchar(a[1]);lcd_putchar(a[2]);lcd_putchar(a[3]);lcd_putchar(a[4]);lcd_putchar(a[5]);
lcd_putchar(a[6]);lcd_putchar(a[7]);lcd_putchar(a[8]);lcd_putchar(a[9]);lcd_putchar(a[10]);lcd_putchar(a[11]);
lcd_putchar(a[12]);lcd_putchar(a[13]);lcd_putchar(a[14]);lcd_putchar(a[15]);

lcd_gotoxy(1,0);
lcd_putchar(a[16]); lcd_putchar(a[17]);
lcd_putchar(a[18]); lcd_putchar(a[19]); lcd_putchar(a[20]); lcd_putchar(a[21]); lcd_putchar(a[22]); lcd_putchar(a[23]);
lcd_putchar(a[24]);
// t=0;
}
}
}

We are a manufacturer of modem, and distributor of Wavecom module for 10 years. We heard you have problem with sending data by XL. We hope you can tell me more and solve it together.

We have the capacity of desinging and making modem, so we also has the problem to do yours'.

Best wishes

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