# How to declare a constant in PHP?

, in category: PHP General , 9 months ago

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by jerad , 8 months ago

﻿@jasen_gottlieb ﻿

In PHP, you can declare a constant using the `define()` function. The `define()` function takes two parameters: the name of the constant and its value. Here is an example:

 ```1 2 ``` ```// Define a constant named PI with the value 3.14159 define('PI', 3.14159); ```

In this example, the `define()` function creates a constant named `PI` with the value `3.14159`. Once a constant is defined, it cannot be changed or redefined throughout the execution of the script.

You can then use the constant in your code by referencing its name, like this:

 ```1 2 ``` ```// Output the value of the constant PI echo PI; ```

This will output the value of the constant `PI`. You can also use constants in expressions, like this:

 ```1 2 3 ``` ```// Calculate the area of a circle with radius 2 using the constant PI \$area = PI * 2 * 2; echo \$area; ```

This will output the area of the circle with radius 2, which is calculated using the constant `PI`.

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by orpha , 17 days ago

﻿@jasen_gottlieb ﻿

To declare a constant in PHP, you can use the const keyword. Here is an example:

 ```1 2 ``` ```// Declare a constant named PI with the value 3.14159 const PI = 3.14159; ```

In this example, the const keyword is used to declare a constant named PI with the value 3.14159. Once a constant is defined, it cannot be changed or redefined throughout the execution of the script.

You can then use the constant in your code by referencing its name, like this:

 ```1 2 ``` ```// Output the value of the constant PI echo PI; ```

This will output the value of the constant PI.

You can also use constants in expressions, like this:

 ```1 2 3 ``` ```// Calculate the area of a circle with radius 2 using the constant PI \$area = PI * 2 * 2; echo \$area; ```

This will output the area of the circle with radius 2, which is calculated using the constant PI.