## Saturday, June 26, 2021

### Function in Python, Javascript and R

A function is what make a code reusable, you write a piece of code once and you use it as many times as you want. These function can either be built-in or custom constructed (user-defined) functions.

Programming languages (Python, Javascript and R in this case) have built in functions. These are functions that are already available by default within the language engine for you to use. There are many of these built-in functions, just to give an example of one lets look at a function that calculates the square root of a number.

### Built-in square root function in Python

In python, this function is available in the built-in math module.
```import math
print(math.sqrt(25))```

### User-defined/Constructed square root function in Python

```def sqrt_num(x):
num_sqrt = x ** 0.5
print(num_sqrt)

sqrt_num(25)```

### Built-in square root function in JavaScript

In JavaScript, this function is available in the built-in math library.
`Math.sqrt(25);`

### User-defined/Constructed square root function in JavaScript

```function sqrt_num(x){
return num_sqrt = x ** 0.5;
}```

### Built-in square root function in R

In R, this function is directly available as seen below.
`sqrt(25)`

### User-defined/Constructed square root function in R

```sqrt_num <- function (x){
num_sqrt = x ** 0.5
print(num_sqrt)
}```

That is it!