Conditionals

Programming languages make it convenient to tell the computer perform an action given a condition. Most general purpose languages have if-statements are switch-cases.

Condition Definition

A condition is something that is needed before something else can happen.

In many programming languages, the condition is a boolean expression.

Boolean Expression

The term boolean expression is used to describe some code that gets evaluated until at its simplest form becoming a boolean true or false.

Evaluation

In an interpreted language like Python, Lua, JavaScript, the interpreter evaluates expressions. An a compiled language, the CPU directly evaluates the program’s expressions.

If-Statements

Here are example of if-statements in different programming languages in the context of returning early from a function that checks for valid arguments.

def need_int(a):
    if not isinstance(a, int):
        return
    return a+1

function need_num(a)
   if typeof(a) ~= "number" then
      return
   end
   return a + 1
end

int needInt(int * int_ptr) {
    // Checking type of pointer using dynamic cast.
    if (int_ptr != nullptr && dynamic_cast<int*>(int_ptr)) {
        return 0;
    }
}

Switch Statements (Or Equivalents)

Switch statements might not exist in newer programming languages. This sections shows the switch-case statements in C++ but it’s not enough as exclusive learning materials. There are also imitations of a switch-case in Python and Lua. In this example, we’re making a simple game menu.

int choice = 2;

switch (choice) {
 case 1:
     std::cout << "Start game\n";
     break;

 case 2:
     std::cout << "Open settings\n";
     break;

 case 3:
     std::cout << "Quit game\n";
     break;

 default:
     std::cout << "Invalid choice\n";
     break;
 }

choice = 2

match choice:
    case 1:
        print("Start game")
    case 2:
        print("Open settings")
    case 3:
        print("Quit game")
    case _:
        print("Invalid choice")

local choice = 2

local actions = {
   [1] = function()
      print("Start")
   end,

   [2] = function()
      print("Settings")
   end,

   [3] = function()
      print("Quit")
   end
}

local action = actions[choice]

if action then
   action()
else
   print("Invalid choice")
end