slides-03-01.qmd

---
title: "more on Functions (class slides)"
format: revealjs
slide-number: true
---

# CSC 110 - More on Functions in Python

## Global vs. Local variables (scope)

-   Every variable that is created has a particular scope
-   The scope of a variable is the region in the code where the variable can be used or modified

## Global vs. Local variables (scope)

-   **Local Variables** have local scope -- for example, a variable assigned inside a function can only be used or modified within that function
-   **Global Variables** have global scope -- for example, a variable delcared outside a function can be accessed or modified across multiple functions

## Global or Local?

```{python}
#| eval: true
#| echo: true
a = 5              
b = 10               

def sum():
    return a + b

def multiply():
    return a * b

def main():
    print(sum())
    print(multiply())

main()
```

## Global or Local?

```{python}
#| eval: true
#| echo: true
def sum(a, b):
    return a + b

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

def main():
    a = 5
    b = 10
    print(sum(a, b))
    print(multiply(a, b))
    a = 10
    print(multiply(a, b))

main()
```

## Argument vs. Parameter

-   Never set variables as global variables, pass values to functions when called
-   When a function is defined, the variables you want to pass to the function are called **parameter variables**
-   When the function is then called, the values you pass to the function are called **arguments**

## Argument or Parameter?

```{python}
#| eval: false
#| echo: true
# The parameters are a and b
def add(a, b):
    return a+b
  
# The arguments being passed through are 5 and 4
add(5, 4)
```

## Write functions

Write two functions: `sphere_area` and `sphere_volume` that calculates the area and the volume of a sphere:

use `3.1415` for $\pi$ and return the rounded value.

$$
a = 4 \cdot \pi \cdot radius^2
$$

$$
v = {4 / 3} \cdot \pi \cdot radius^3 
$$
Name your file as `sphere.py` and submit to gradescope.

Test case:
```{python}
#| echo: true
#| eval: false
r = 0.75
print(sphere_area(r)) # 7.07
print(sphere_volume(r)) # 1.77
```


## Write functions -- solutions 1

```{python}
#| echo: true
#| eval: true
def sphere_area(radius):
  "calculates the area of a sphere of given radius"
  area = 4 * 3.1415 * radius**2
  return round(area, 2)

def sphere_volume(radius):
  "calculates the volume of a sphere of given radius"
  volume = (4 / 3) * 3.1415 * radius**3
  return round(volume, 2)

def main():
  r = .75
  v = sphere_volume(r)
  a = sphere_area(r)
  print(v, a)

main()
```

## Write functions
Comparing two formulas:
$$
a = 4 \cdot \pi \cdot radius^2
$$

$$
v = {4 / 3} \cdot \pi \cdot radius^3 
$$
We can use area when calculating volume:
$$
v = {1 / 3} \cdot a \cdot radius
$$

Modify your `sphere_volume` function by calling `sphere_area` inside the function.

## Write functions -- solutions 2

```{python}
#| echo: true
#| eval: true
def sphere_area(radius):
  "calculates the area of a sphere of given radius"
  area = 4 * 3.1415 * radius**2
  return round(area, 2)


def sphere_volume(radius):
  "calculates the volume of a sphere of given radius"
  volume = (1 / 3) * sphere_area(radius) * radius
  return round(volume, 2)


def main():
  r = .75
  v = sphere_volume(r)
  a = sphere_area(r)
  print(v, a)

main()
```

## Function Comments

-   Every function created is required to have a function comment, including main
-   Function comments are a multi-line string (as opposed to using `#` for other comments)

## Function Comments

```{python}
#| echo: true
#| eval: true
'''
Xinchen Yu
CSC110
Class Demonstration
This program has two functions: one to calculate the area of a sphere,
the other to calculate the volume of a sphere.
The main() function is called to print to the standard output the
area and volume of a sphere of radius .75
'''
def sphere_area(radius):
  '''
  This function calculates the area of a sphere of given radius.
  Args:
    radius: integer representing the radius of the sphere
  Returns:
    The float representing the area of a sphere of the given radius
  '''
  area = 4 * 3.1415 * radius**2
  return round(area, 2)

def sphere_volume(radius):
  '''
  This function calculates the volume of a sphere of given radius.
  Args:
    radius: integer representing the radius of the sphere
  Returns:
    The float representing the volume of a sphere of the given radius
  '''
  volume = (1 / 3) * sphere_area(radius) * radius
  return round(volume, 2)

def main():
  '''
  This function prints the area and volume of a sphere of radius .75.
  Args:
    None
  Returns:
    None
  '''
  r = .75
  a = sphere_area(r)
  v = sphere_volume(r)
  print(a, v)
  
main()
```


## Function to calculate the volume of a cylinder

Write a function that does the following:

1.  Its name is `volume`
2.  It takes two integer arguments: `radius` and `height`
3.  It calculates the volume of a cylinder, based on `radius` and `height`. Volume is area multiplied by height.
4.  It returns the float value for calculated volume.


## Function to calculate the volume of a cylinder

```{python}
#| echo: true
#| eval: false
def volume(radius, height):
  # calculate the area first
  area = 3.1415 * radius ** 2
  
  # multiply area by height
  vol = area * height
  
  # return calculated volume
  return vol

def main():
  print(volume(1, 2)) # 6.283
  print(volume(6, 10)) # 1130.94
  print(volume(5, 5)) # 392.68750000000006
  
main()
```