# Functions - one parameter

## Parameter

A parameter is like a placeholder.  When a function is called, you pass a value to the parameter.

|                                  |                                                                                                                                          |
| -------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------- |
| 1 def function\_name(parameter): | The keyword def indicates a function is defined.  function\_name must follow variable naming rules.  Parameter is passed in parenthesis. |
| 2     \<indented block>          | Indented code to perform some action.                                                                                                    |

### Example 1

Write a function that squares a number.  In the menu option, ask the user for a number.  Call the function square with the user’s number as the value.\
Create a function named square. Print the square of the number.<br>

{% code title="example1.py" %}

```python
def main():
  done = False
  while not done:
    print("Menu")
    print("E1 - Example 1")
    print("Q - Quit")
    choice = input("Choice: ")
    if choice == "E1":
        num = int(input("Give me a number: "))
        square(num)
    elif choice == "Q":
        print("Exiting Game!")
        done = True

def square(num):
  print(num, "squared is", num**2)

main()

```

{% endcode %}

### Example 2

Write a function that determines if a number is even. In the menu option, ask the user for a number.  Call the function even with the user’s number as the value. Create a function named even. If the number is even, print the number is even.

{% code title="example2.py" %}

```python
def main():
  done = False
  while not done:
    print("Menu")
    print("E2 - Example 2")
    print("Q - Quit")
    choice = input("Choice: ")
    if choice == "E2":
        num = int(input("Give me a number: "))
        e1(num)
    elif choice == "Q":
        print("Exiting Game!")
        done = True

def even(num):
  if num % 2 == 0:
    print(num, "is even")

main()
```

{% endcode %}

### Example 3

Write a function that calculates the summation of a number.   In the menu option, ask the user for a number.  Call the function summation with the user’s number as the value. Create a function named summation.

{% code title="example3.py" %}

```python
def main():
  done = False
  while not done:
    print("Menu")
    print("E3 - Example 3")
    print("Q - Quit")
    choice = input("Choice: ")
    if choice == "E3":
        num = int(input("Give me a number: "))
        e1(num)
    elif choice == "Q":
        print("Exiting Game!")
        done = True

def summation(num):
  print(num*(num+1)/2))

main()
```

{% endcode %}

\ <br>