In this example, x, y, and z, are variables:
From the example above, you can expect:
In this example, price1, price2, and total, are variables:
In programming, just like in algebra, we use variables (like price1) to hold values.
In programming, just like in algebra, we use variables in expressions (total = price1 + price2).
From the example above, you can calculate the total to be 11.
These unique names are called identifiers.
Identifiers can be short names (like x and y), or more descriptive names (age, sum, totalVolume).
The general rules for constructing names for variables (unique identifiers) are:
This is different from algebra. The following does not make sense in algebra:
(It calculates the value of x + 5 and puts the result into x. The value of x is incremented by 5.)
In programming, text values are called text strings.
Strings are written inside double or single quotes. Numbers are written without quotes.
If you put quotes around a number, it will be treated as a text string.
After the declaration, the variable is empty (it has no value).
To assign a value to the variable, use the equal sign:
You can also assign a value to the variable when you declare it:
In the example below, we create a variable called carName and assign the value "Volvo" to it.
Then we "output" the value inside an HTML paragraph with id="demo":
|It's a good programming practice to declare all variables at the beginning of a script.|
You can declare many variables in one statement.
Start the statement with var and separate the variables by comma:
A declaration can span multiple lines:
In computer programs, variables are often declared without a value. The value can be something that has to be calculated, or something that will be provided later, like user input.
A variable declared without a value will have the value undefined.
The variable carName will have the value undefined after the execution of this statement:
The variable carName will still have the value "Volvo" after the execution of these statements:
You can also add strings, but strings will be concatenated (added end-to-end):
Also try this:
|If you add a number to a string, the number will be treated as string, and concatenated.|