If Statements
Understanding Program Flow
Programs are said to have a "flow of execution". You start by executing a line of code, then the next, then the next, and so on.
A flow chart is a common visual used to represent the various paths of execution that your program might take. Many people use them to help plan programs.
- This flow chart depicts a program executing one line after another until it gets to a point where it needs to make a decision.
- In order to determine which path to take you state some condition. It should be a Boolean expression - something that evaluates to true or false. Here we have a simple comparsion of two values: the person's age and the number 18.
- The program does one thing if the condition is true, and something else if the condition is false.
- The program can continue a single thread of execution after the condition as well.
How If-statements work
if statements are the lines of code you use to change the flow of a program while it's running. You can write code that determines which lines of code should run next.
At the right is a diagram showing the elements of a basic if statement in JavaScript.
There are two basic parts to an if-statement.
- A condition to be evaluated (A Boolean expression that evaluates to true or false)
- Code that should run if the expression was true - enclosed in curly braces
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