Key Concepts

Review core concepts you need to learn to master this subject

Control Flow

In programming, control flow is the order in which statements and instructions are executed. Programmers are able to change a program’s control flow using control structures such as conditionals.

Being able to alter a program’s control flow is powerful, as it lets us adapt a running program’s behavior depending on the state of the program. For example, suppose a user is using a banking application and wants to withdraw $500. We certainly want the application to behave differently depending on whether the user has $20 or $1000 in their bank account!

Conditional Control

Conditional statements or conditional control structures allow a program to have different behaviors depending on certain conditions being met.

Intuitively, this mimics the way humans make simple decisions and act upon them. For example, reasoning about whether to go outside might look like:

  • Condition: Is it raining outside?
    • If it is raining outside, then bring an umbrella.
    • Otherwise, do not bring an umbrella.

We could keep adding clauses to make our reasoning more sophisticated, such as “If it is sunny, then wear sunscreen”.

  1. 1
    This lesson requires you to know the basics of hamburger-making: Place the bread down Add the burger patty Add the pickles Place the bread on top What if you had to say each step every tim…
  2. 2
    Instead of giving those instructions for every hamburger, we can group and name them as a single function: function makeHamburger() { Add bread Add burger patty Add pickles Add bread } …
  3. 3
    Not everyone wants to eat hamburgers. We could write a new function for each new sandwich type, but that takes a lot of work and risks making mistakes. Instead we’ll generalize the hamburger fu…
  4. 4
    A sandwich wouldn’t be complete without fries and dessert! Here are the instructions to make the complete meal: * Add bread, Add burger patty, Add fried potatoes, Add pickles, Add bread, Add salt…
  5. 5
    Time to get coding! It’s okay if you don’t recognize all the symbols in this code: we’ll walk you through the parts you need to know. The makeSandwich() function is provided in main.js. It is …
  6. 6
    Well done! Functions are a fundamental concept in programming, and learning the basics will serve you wherever your path leads, regardless of language or domain. To review: * A function is a sequ…
  1. 1
    How do computers make decisions? Here are a few examples: Web surfing: Open the browser, load the text, load the images. Social media: If the user’s profile is private, hide their posts. Other…
  2. 2
    If the user’s profile is private, hide their posts. Otherwise, make them visible. Computers can run instructions on their own, leaving us to work on more interesting and creative problems. But c…
  3. 3
    Repeat a sound four times a measure. Computers are good at repetitive tasks: they exactly follow instructions and perform them quickly. But if the programmer has to write the same instructions f…
  4. 4
    Collect shipping and email address. Reject a purchase if either is incorrect. Errors, or exceptions, happen all the time in programming. You can’t escape them. But you can handle them gracefully…
  5. 5
    Let’s recreate the conditional control structure using JavaScript! (The one about social media posts, remember?) ![Diagram of conditional control structure](https://s3.amazonaws.com/codecademy-c…
  6. 6
    Well done! Control flow is a fundamental concept in programming, and learning the basics will serve you wherever your path leads, regardless of language or domain. In review: - Control flow is t…

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