slides-04-03.qmd

---
title: "if elif else statements (slides)"
format: revealjs
slide-number: true
---

# CSc 110 if elif else statements

## if elif else

While the if condition is required, the elif and else statements are not.

`elif` is saying 'if the previous conditions were not true, then try this condition'. It forces the cases to be mutually exclusive.

```{html}
if conditionA:
    statements
elif conditionB:
    statements
elif conditionC:
    statements
else:
    statements
```


## Compare the functions

```{python}
#| eval: true
#| echo: true
def func_one(a):
  message = ""
  if a >= 18:
    message += 'You may apply to join the military.'
  if a >= 35:  # independent from a >= 18
    message += ' You may run for president.'
  return message

def func_two(a):
  message = ""
  if a >= 18:
    message += 'You may apply to join the military.'
  elif a >= 35:  # only runs when a >= 18 is False
    message += ' You may run for president.'
  return message

def main():
  print(func_one(40))
  print(func_two(40))
  
main()
```


## Write a function

Write a function that does the following:

1. Its name is `max_of_two`
1. It takes two numeric arguments
1. It returns the highest value

Test cases

```{python}
#| eval: false
#| echo: true
print( max_of_two(-1, 3) ) # 3
print( max_of_two(-1, -3) ) # -1
print( max_of_two(5, 5) ) # 5
```

## Write a function -- solution

```{python}
#| eval: true
#| echo: true
def max_of_two(x, y):
  if x >= y:
    return x
  else:
    return y

def main():
  print( max_of_two(-1, 3) ) # 3
  print( max_of_two(-1, -3) ) # -1
  print( max_of_two(5, 5) ) # 5

main()
```


## Write a function

Write a function that does the following:

1. Its name is `max_of_three`
1. It takes three numeric arguments
1. It returns the highest value

Name your file `max_of_three.py` and submit to Gradescope.

Test cases:

```{python}
#| eval: false
#| echo: true
print( max_of_three(-1, 3, 3) ) # 3
print( max_of_three(-1, -3, 0) ) # 0
print( max_of_three(5, 5, 10) ) # 10
```

## Write a function -- solution 1

```{python}
#| eval: true
#| echo: true
def max_of_three(x, y, z):
  if x >= y and x >= z:
    return x
  elif y >= x and y >= z:
    return y
  else:
    return z

def main():
  print( max_of_three(-1, 3, 3) ) # 3
  print( max_of_three(-1, -3, 0) ) # 0
  print( max_of_three(5, 5, 10) ) # 10

main()
```

## Write a function -- solution 2

```{python}
#| eval: true
#| echo: true
def max_of_three(x, y, z):
  max_value = x
  
  if y >= max_value:
    max_value = y
    
  if z >= max_value:
    max_value = z
    
  return max_value

def main():
  print( max_of_three(-1, 3, 3) ) # 3
  print( max_of_three(-1, -3, 0) ) # 0
  print( max_of_three(5, 5, 10) ) # 10

main()
```

## Write a function -- solution 3

```{python}
#| eval: true
#| echo: true
def max_of_two(x, y):
  if x >= y:
    return x
  else:
    return y

def max_of_three(x, y, z):
  max_x_y = max_of_two(x, y)
  return max_of_two(max_x_y, z)

def main():
  print( max_of_three(-1, 3, 3) ) # 3
  print( max_of_three(-1, -3, 0) ) # 0
  print( max_of_three(5, 5, 10) ) # 10

main()
```



## Write a function

Write a function that does the following:

1.  Its name is `average_of_highest`
2.  It has three numeric parameters: `x`, `y` and `z`
3.  It returns the average of the two highest of the three arguments
4.  Test cases:
    1.  arguments `1`, `3`, `4` should return `3.5`

    2.  arguments `6`, `4`, `2` should return `5.0`

    3.  arguments `4`, `2`, `1` should return `3.0`

## Write a function - solution

```{python}
#| eval: true
#| echo: true
def average_of_highest(x, y, z):
  if x >= z and y >= z:
    return (x + y) / 2
  elif y >= x and z >= x:
    return (y + z) / 2
  else:
    return (x + z) / 2
  
def main():
  print( average_of_highest(1, 3, 5) ) # should print 4.0
  print( average_of_highest(6, 4, 2) ) # should print 5.0
  print( average_of_highest(4, 2, 1) ) # should print 3.0
  print( average_of_highest(2, 2, 1) ) # should print 2.0
  print( average_of_highest(2, 1, 2) ) # should print 2.0
  print( average_of_highest(1, 2, 1) ) # should print 1.5
  
main()
```