Cairo: let vs tempvar what is the difference?

Imagine you have the following code:

tempvar x = 2;
let y = x * x * x;
let z = y * y * y;
serialize_word(z);

Because of the lets, the serialize_word(z) is equivalent to serialize_word(x * x * x * x * x * x * x * x * x) .

"tempvar" stands for "temporary variable", which means that a variable will be allocated for the intermediate values (x * x * x and y * y * y). If you change the two lets to tempvars and run the program this reduces the same computation to use only 4 steps and 2 new variables.

let is used to declare a reference. let keyword doesn't create an instruction, it simply replace reference by value. Example, everywhere I use x, compiler will replace it by 10.

let x = 10;
serialize_word(x);

equivalent to

serialize_word(10);

tempvar is used to declare a variable. It means we will take memory to store my variable. And tempvar keyword will create an instruction.