functions.md

Functions

Setup

Install python if you haven't already

macOS

brew install python

Ubuntu

sudo apt-get install python
sudo apt-get install python-pip

Install node if you haven't already

Mac

brew install node

Ubuntu

sudo apt-get install nodejs

Defining a function

A function has inputs and an output. The inputs are known as the "arguments", and the output is known as a "return value"

below is an example of a function in python

def multiply(a,b):
	return a * b

this is an example of the same function in javascript

function multiply(a,b) { 
	return (a * b)
}

This function takes two arguments (a and b), and returns the value of them multiplied together

Calling a function

In the above exercise you have simply defined a function, but you haven't asked python to call it. If you ran the program above, you wouldn't see any output in the terminal.

# This part of the code defines a function
def multiply(a,b):
	return a * b

# This part of the code then calls that function and assigns the variable x to its return value
x = multiply(8,9)

# This prints x to the terminal for humans to read
print x

in JavaScript that would look like this

// This part of the code defines a function
function multiply(a,b) { 
	return (a * b)
}

// This part of the code then calls that function and assigns the variable x to its return value
var x = multiply(8,9)

// This prints x to the terminal for humans to read
console.log(x)

Return vs Print

The function can also contain other logic and do other things. For example, you could write the function above like this:

def multiply(a,b):
	print "I'm multiplying two numbers"
	return  a * b

This would both print to the terminal and return a value. The return is the very last logical thing that happens in the execution of a function. Once a return is called, no additional code can be run inside the function. The same is true in JavaScript (and all programming languages).

Try It

1. create a new branch in your assignments git repo called "calculator"

2. inside that branch create a new file called calculator.py

3. Write a program that defines four functions (multiply, add, subtract, and divide). These functions should not print anything, they should simply perform a mathematical operation on the two arguments and return the value.

4. Commit to git git commit -m "add functions to calculator"and push the change to github. git push

5. At the bottom of the file, Call the function and print a line explaining what is happening. Like this:

   print "I'm going use the calculator functions to multiply 5 and 6"
   x = multiply(5,6)
   print x

6. Commit this change and explain what you just did in the commit message

7. Run the file with the following command to make sure your python is all right:

   python2 calculator.py
   

8. Make sure everything works correctly and issue a pull request on github back to the master branch with a message explaining what changes you made in this branch.

9. Accept the pull request into the master branch and delete the calculator branch on github.

10. Checkout the master branch, and pull the version of master with the calculator branch merged

    git checkout master
    git pull
    

11. Delete your local version of the calculator branch

    git branch -D calculator
    

bonus

1. Add two more functions, square and cube.
2. Make a function called square_n_times that takes two arguments, number and n. square the number n times and return the result.

Try It

1. create a new branch in your assignments git repo called "js-calculator"

2. inside that branch create a new file called calculator.js

3. Write (in javascript) a program that defines four functions (multiply, add, subtract, and divide). These functions should not print anything, they should simply perform a mathematical operation on the two arguments and return the value.

4. Commit to git git commit -m "add functions to calculator"and push the change to github. git push

5. At the bottom of the file, Call the function and print a line explaining what is happening. Like this:

   console.log("I'm going use the calculator functions to multiply 5 and 6")
   var x = multiply(5,6)
   console.log(x)

6. Commit this change and explain what you just did in the commit message

7. Run the file with the following command to make sure your python is all right:

   node calculator.js
   

8. Make sure everything works correctly and issue a pull request on github back to the master branch with a message explaining what changes you made in this branch.

9. Accept the pull request into the master branch and delete the js-calculator branch on github.

10. Checkout the master branch, and pull the version of master with the calculator branch merged

    git checkout master
    git pull
    

11. Delete your local version of the js-calculator branch

    git branch -D js-calculator