unsigned char keypad()
{
    unsigned char i,temp=0,temp1=0,temp2=0xff,wait=0;//,wait1=0;
    bit flag_x=0;
    while(1)
    {
        //write program to prevent indefinite waiting here
        //wait++;
        timer_50();
        hex = 0x0f;
        //delay_ms(10);

        for(i=0; i<4; i++)
        {
            if(i==0)        hex = temp1 = 0xEF;
            else if(i==1)   hex = temp1 = 0xDF;
            else if(i==2)   hex = temp1 = 0xBF;
            else if(i==3)   hex = temp1 = 0x7F;

            temp = hex;
            temp &= 0x0f;
            temp1&= 0xf0;
...