What are the types of the following expressions and what do they evaluate to, and why?

let seventeen : int = 17;;
let eleven : int = 1 + 2 * 3 + 4;; (* 11 *)
let one : int = 800 / 80 / 8;; (* 1 *)
let a : bool = (400 > 200) = true;;
let b : bool = (1 <> 1) = false;;
let c : bool = (true || false) = true;;
let d : bool = (true && true) = true;;
let e : bool = (if true then false else true) = false;;
let f : char = '%';;
(* 'a' + 'b' -> Error! *)

Consider the evaluations of the expressions 1 + 2 mod 3, (1 + 2) mod 3, and 1 + (2 mod 3). What can you conclude about the + and mod operators?

(mod) has higher precendece than (+).

A programmer writes 1+2 * 3+4. What does this evaluate to? What advice would you give them?

let expr : bool = (1+2 * 3+4) = 11;;

(* my suggestion would be to rewrite as follows *)
let expr' : bool = ((1 + 2) * (3 + 4)) = 21;;

The range of numbers available is limited. There are two special numbers: min_int and max_int. What are their values on your computer? What happens when you evaluate the expressions max_int + 1 and min_int - 1?

min_int = (-4611686018427387904);;
max_int = 4611686018427387903;;

(* when we add to max_int or subtract from min_int, we loop around *)
(min_int - 1) = max_int;;
min_int = (max_int + 1);;

What happens when you try to evaluate the expression 1 / 0? Why?

We get an Exception, because we can't divide by zero.

Can you discover what the mod operator does when one or both of the operands are negative? What about if the first operand is zero? What if the second is zero?

Hmmm...

Why not just use, for example, the integer 0 to represent false and the integer 1 for true? Why have a separate bool type at all?

Because then we limit the range of possible inputs two bool, instead of int which has a ridiculous amount of possibilities.

What is the effect of the comparison operators like < and > on alphabetic values of type char? For example, what does 'p' < 'q' evaluate to? What is the effect of the comparison operators on the booleans, true and false?

For bool values, true is GT false. For char values it checks for order. i.e. 'a' comes before 'g', therefor LT.