* Robust programming means writing programs that can cope with errors. One example would be to use **data validation** to avoid incorrect input.
* Secure programming means writing programs that use security features such as passwords
You must check your validation with normal, boundary and erroneous data.
# Examples
**NOTE: All the following use while loops, not ifs! Why?**
The following code checks that a value is entered
```python
ans = input("Enter your choice")
while ans == "":
ans = input("You must enter a value")
```
Test data: Erroneous: "" Normal: "Pizza"
The following code checks that the username is at least 6 characters long
```python
ans = input("Choose your username")
while len(ans) <6:
ans = input("Username must be at least 6 characters")
```
Test data: Erroneous: "Pizza" Normal: "Hamburger"
The following checks that someone is aged between 11 and 18
```python
age = int(input("Enter your age: "))
while age < 11 or age > 18:
age = int(input("Age must be between 11 and 18 "))
```
Test data: Erroneous: 8 Boundary: 11 Normal: 15
The following checks that someone is in a year 9 form
```python
forms = ["9b","9h","9bh","9l","9m","9lm","9r","9w","9rw"]
f = input("Enter your form group: ").lower()
while f not in forms:
f = input("Not a valid form group: ").lower()
```
Test data: Erroneous: "8qt" Normal: "9l"
# Exercise
Write code to perform the following validation checks.
1. Jockey club names cannot be more than 18 characters long. Write a validation check for these names. Test with the normal data "Ariel" and the erroneous data "supercalifragilisticexpialidocious"
2. Modify your answer to question 1 so that blank names are also rejected
3. Police officers in the UK are aged between 18 and 60. Write a validation check for this. Test your code with the following data: 25, 60 and 81
4. A cafe sells the following drinks: tea, black coffee, white coffee, hot chocolate, lemonade. Write a validation check for the above drinks.
# Extension
The following code demonstrate the **in**, **startswith** and **endswith** functions
```python
>>> s ="I never saw a purple cow"
>>> s.endswith("cow")
True
>>> s.startswith("I")
True
>>> "never" in s
True
```
Use them to write validation checks for the following:
This is an example of a URL: [http://blue-coat.org](http://blue-coat.org/)
1. URL check: does it end in .com or .org?
2. Does it start with [http://](http:) or [https://](https:)
3. Simple check for email: does the string contain an '@'?
4. More complex email check: does a string contain '@' and end with .com or .org?