# 2: Functions
**Source**: https://cscircles.cemc.uwaterloo.ca/2-functions/
**Parent**: https://cscircles.cemc.uwaterloo.ca/
We have seen one function already, `print()`, which outputs a message. To use a function you always write its name, followed by some *arguments* in parentheses `()`. The word *argument* basically means an input to the function. Then, the function does some action depending on its arguments. When there are multiple arguments to a function, you separate them with commas (`,`). For example, you can give multiple arguments to `print`; it will print all of them in order, with spaces separating them. We demonstrate in the example below.\
Example
Print three numbers
x = 3
print(x, x + x , x \* x)
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| | The extra spaces in the sample program above had no effect on the output. Extra spaces are meaningless in most other situations too. However, be careful that *extra space at the **beginning** of a line*, called *indenting*, has a special meaning that can [cause errors (click for an example)](https://cscircles.cemc.uwaterloo.ca/console/?consolecode=print%28%22This%20line%20is%20ok%22%29%0A%20print%28%22This%20one%20starts%20with%20a%20space%22%29) if used incorrectly. You will see correct indenting a few lessons later. |
A function may also give back a value (like an output). For example the function `max()` (short for *maximum*) gives back the largest out of all of its arguments, which must be numbers.\
Example
*Try to predict the output of the following program, before you run it.*
print(max(42, 17))
print(max(128,281,812))
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The name *return value* means the value that a function gives back. For example in `max(42, 17)` we say that "the function `max` returned the value `42`."
The `max` function has a friend which behaves similarly: the `min` function returns the *minimum* (smallest) of its arguments.
Multiple Choice Exercise: Min and Max I
What is the output of the following program?
```
x = 13\
y = 7\
a = max(x+y, x*2)\
b = min(x, y)\
print(a,b)
```
Your choice: Select one7 2626 720 1313 20
Correct!
Functions can be combined to create more complicated expressions.\
Short Answer Exercise: Min and Max II
What is the output of the following program? Hint
```
x = min(max(13, 7), 9)\
print(x)
```
Your answer (enter a number):
Correct!
You are not limited to using functions that are pre-defined in Python. In a few lessons you will learn how to define new functions!
## Common Errors
If you call a function with not enough arguments (inputs) or too many arguments, you get an error. For example, `max` requires at least one input:
Example
Calling `max` with too few arguments.
max()
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It's very important to carefully read the errors that you get back, when your code doesn't work. Python will usually give you helpful feedback on what went wrong. However, sometimes you need to look around a little bit to diagnose the problem — here's an example.
Example
Press **Run program** and look at the error that occurs.
smaller = min(14, 99
bigger = max(3, 4)
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Python says there is a syntax error, which means it can't understand what you're trying to do:
```
Traceback (most recent call last):
In line 2 of the code you submitted:
bigger = max(3, 4)
^
SyntaxError: invalid syntax
```
However, the line `bigger = max(3, 4)` is actually fine. The problem actually spilled over from the previous line: we forgot to add the closing parenthesis `)` after `smaller = min(14, 99` and Python started looking at the next line for the `)`. So, check the lines before and after what Python suggests, if you are stuck debugging your programs.
## Exercise
This is a two-part exercise using the `min` and `max` functions. There are connections between the cities of Maxime and Miniac with several bridges. There is a separate limit on the amount of weight that can be transported across each bridge.
Coding Exercise: One Road
For part 1, there is a single road between the two cities. The road has three bridges with weight limits `a`, `b`, `c`, as shown in the picture below:
In order to drive along the route, your truck needs to drive first over the bridge with weight limit `a`, then the one with weight limit `b`, then the one with weight limit `c`. Your truck will crash if you overload *any* of the three weight limits. *Write a program that prints out the maximum weight that can be transported along this road.* Your code should assume that the variables `a`, `b`, and `c` already contain the bridge weight limits.
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