Lesson: Nested Conditionals

What are Nested Conditionals?

A nested conditional is a conditional statement inside another conditional statement, or an if statement within an if statement.
This allows us to check multiple conditions in a structured way, which is useful when decisions depend on more than one factor

For example:

  • First, check if a main condition is true.
  • Then, only if it’s true, check an additional condition inside it.

The examples below uses if and else statments to form a nested conditional in both Python and Java.


# Example of a nested conditional in Python

age = 18 ##Sets age variable
has_id = True ##Sets has_id variable

if age >= 18: ##Checks if age is 18 or older
    if has_id: ##Checks if the person has an ID
        print("You are allowed to enter.") 
    else: ##If the person does not have an ID
        print("You need an ID to enter.")
else: ##If the person is younger than 18
    print("You are too young to enter.")



// Example of a nested conditional in JavaScript

let age = 18;
let hasID = true;

if (age >= 18) {
    if (hasID) {
        console.log("You are allowed to enter.");
    } else {
        console.log("You need an ID to enter.");
    }
} else {
    console.log("You are too young to enter.");
}

How the example works:

  1. The program first checks if age >= 18.
  2. If False, it immediately goes to the else branch.
  3. If True, it goes inside and checks the nested condition if has_id.
  4. Depending on if the if statement is true or false, a different final result is printed.

Snake Game Example

Heres an example of a nested conditional in our Snake Game Hack. In this example, the nested conditional is used to check whether or not the snake hits a wall, losing a life if they do.

// Wall Checker
            if(wall === 1){
                // Wall on, Game over test
                if (snake[0].x < 0 || snake[0].x === canvas.width / BLOCK || snake[0].y < 0 || snake[0].y === canvas.height / BLOCK){
                    loseLife();
                    return;
                }
            }else{
                // Wall Off, Circle around
                for(let i = 0, x = snake.length; i < x; i++){
                    if(snake[i].x < 0){
                        snake[i].x = snake[i].x + (canvas.width / BLOCK);
                    }
                    if(snake[i].x === canvas.width / BLOCK){
                        snake[i].x = snake[i].x - (canvas.width / BLOCK);
                    }
                    if(snake[i].y < 0){
                        snake[i].y = snake[i].y + (canvas.height / BLOCK);
                    }
                    if(snake[i].y === canvas.height / BLOCK){
                        snake[i].y = snake[i].y - (canvas.height / BLOCK);
                    }
                }
            }

Calculator Example

Heres another example of a nested conditional, this time in our calculator hack. In this example, multiple nested conditionals are used to do multiple things:

  1. Distinguishing between digits and decimal points
  2. Overwrting the display when inputing new numbers
  3. prevent leading zeros
  4. Allowing only 1 decimal per number
// Number action
function number (value) { // function to input numbers into the calculator
    if (value != ".") {
        if (nextReady == true) { // nextReady is used to tell the computer when the user is going to input a completely new number
            output.innerHTML = value;
            if (value != "0") { // if statement to ensure that there are no multiple leading zeroes
                nextReady = false;
            }
        } else {
            output.innerHTML = output.innerHTML + value; // concatenation is used to add the numbers to the end of the input
        }
    } else { // special case for adding a decimal; can't have two decimals
        if (output.innerHTML.indexOf(".") == -1) {
            output.innerHTML = output.innerHTML + value;
            nextReady = false;
        }
    }
}

Nested Conditionals MC

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Question 1

What is a nested conditional?

  • A) Two separate if statements next to each other
  • B) An if statement inside another if statement
  • C) A while loop inside an if statement
  • D) A conditional that always runs no matter what

Question 2

What will the following Python code print?

age = 18
has_id = False

if age >= 18:
    if has_id:
        print("You are allowed to enter.")
    else:
        print("You need an ID to enter.")
else:
    print("You are too young to enter.")
  • A) You are allowed to enter.
  • B) You need an ID to enter.
  • C) You are too young to enter.
  • D) Nothing will print.

Question 3

In the nested condition below, what condition must be true for “Access Granted” to print?

if username == "admin":
    if password == "1234":
        print("Access Granted")
  • A) Only username is correct
  • B) Only password is correct
  • C) Both username and password are correct
  • D) Either one is correct