What is a C code fall through and compiling with/without optimization? [closed]

Answer 1

Fallthough is when a switch case "falls through" to another case:

switch(someInt) {
case 0:
    // Do stuff
case 1:
    // Do more stuff
    break;
}

In this example, if someInt is 0, it will execute both commented sections of code before hitting the break statement, which exits the switch. Forgetting to put in a break after each switch section is a common beginner error. If you want to make case 0 only execute it's own code and not the code for case 1, it would look like this:

switch(someInt) {
case 0:
    // Do stuff
    break;
case 1:
    // Do more stuff
    break;
}

Compiling with optimization simply refers to using the optimization option to let the compiler figure out ways to speed up or simplify the program.