If-else statement

Sometimes, one condition is not enough, and for that, in TypeScript (as in other programming languages), there is the if-else construct. For example, if you need to create a calculator, you, as a true programmer, will do it using the if-else construct, like this:


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let a: number = 5;
let b: number = 10;
let operator: string = '*';
if (operator == '+') {
    console.log(a + b);
} else if (operator == '-') {
    console.log(a - b);
} else if (operator == '*') {
    console.log(a * b);
} else if (operator == '/') {
    console.log(a / b);
} else {
    console.log(`Error, there is no ${operator} operator!`)
}

In this code, we have 3 variables: number a, number b, and the operation that will be performed between them. Using the if-else construct, we determine which operation will be applied to these two numbers. If we don't find a suitable operation, we will display a message indicating that such an operation is not available!

Now let's take a closer look at the syntax we're using:

Note that if one of the conditions is met, we exit the if-else statement, and the remaining blocks are ignored.

Unlike else if, the else block does not have a condition block. This is because else executes only if all previous conditions were false.

The if-else construct is often used for a variety of tasks, from checking if a number is positive to writing artificial intelligence.

You can also choose not to use else-if blocks and use only if and else, for example:


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let num: number = 15;
if (num >= 0) {
    console.log('The number is positive!');
} else {
    console.log('The number is negative');
}

This way, we can experiment and use such a construct for various purposes!

1. What is the purpose of the `if-else` statement in TypeScript?

2. In an `if-else` statement, what is executed if the condition inside the `if` block is false?

Everything was clear?

Section 2. Chapter 3