char DS1620_Temperature_Array(){
char temperature_array [20];
	int i;
	for (i = 0; i < 21; i++){
		int get_temp, MSB; 
		float temperature;
		get_temp = DS1620_Read(0xAA, 9);
		temperature = (float) get_temp * 0.5;	
		MSB = get_temp >>7;
		if ( MSB > 0 ) temperature = temperature - 256;
		temperature_array [i] = temperature;
		HW_DELAY_50ms();
		}
return (temperature_array);
}

This post, as not directly related to 8051, belongs to the General Chat.

Also, please read the FAQ on how to post formatted code.

The questions you presented are rather trivial and you should perhaps go through some general programming textbook first. Just conceptually:

Q1: add up all members of the array and divide by their number

Q2: assume max is the first member of the array; then go through rest of the array and if some of the member is higher, replace max by this member.

JW