Code Eyzi

# Conditions

Let's talk about one of the common data types that we brushed over -- boolean. A boolean is simply either true or false. Despite only having two possible values for its type, it is more used than any other type. It is a great type to use when dealing with decisions, which most program needs to do.

boolean isLegalAge(int age) {
  if (age < 18) {
    return false;
  } else {
    return true;
  }
}

In this example, we have a function that determines whether the given age is legal or not, which we determine if the given age is below 18 or not. If it is below 18, the age is not (false) legal. Otherwise, it is (true).

Inside the parenthesis (()) following the if clause, there is a statement (age < 18). This also returns a true or false value when evaluated. When it is true, the code within the if block -- everything inside the curly brackets following if ({}) -- would execute. Otherwise, it would execute the else block.

To sum it up, if the input age is below 18, that is, if age < 18 evaluates to true, then return false; statement would run. If it's not, then the return true; statement would run instead.

# Equality

Operators for equality are common in languages. < for less than, > for greater than, <= for less than or equal to, >= for greater than or equal to. Since most language has = as a variable assignment operator, == is used to evaluate equality. And to evaluate inequality, a bang (!) is often used with it -- !=

  • age < 18: is age less than 18?
  • age <= 18: is age less than or equal to 18?
  • age > 18: is age greater than 18?
  • age >= 18: is age greater than or equal to 18?
  • age == 18: is age 18?
  • age != 18: is age not 18?

But wait! Since age < 18 returns a boolean value already, can't we just use it as return somehow?

Correct! The if statement in this case feels redundant. For this particular case, we can just return the negated equivalent of age < 18. Which, instead of checking if it's below 18, let's check if it is 18 or above.

boolean isLegalAge(int age) {
  return age >= 18;
}

# Multi-conditional

On top of the if-else statement, languages can also have support for multiple conditional statements. Commonly, there would be an else if statement or what's known as a switch-case statement.

function toOrdinalForm(singleDigit) {
  if (singleDigit == 1) {
    return "1st"
  } else if (singleDigit == 2) {
    return "2nd"
  } else if (singleDigit == 3) {
    return "3rd"
  } else {
    return singleDigit + "th"
  }
}

or the switch-case alternative would be something like

function toOrdinalForm(singleDigit) {
  switch (singleDigit) {
    case 1: return "1st"
    case 2: return "2nd"
    case 3: return "3rd"
    default: return singleDigit + "th"
  }
}

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