# 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 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.

example1.py
``````def main():
done = False
while not done:
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()
``````

### 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.

example2.py
``````def main():
done = False
while not done:
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()``````

### 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.

example3.py
``````def main():
done = False
while not done:
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()``````

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