Loops

You could always use a while loop.
while loops are condition controlled.
for loops are count controlled.
Use a while loop when you don't know how many times it will have to repeat, like a user entering bad input.
There must always be something inside the loop that changes the loop condition. If not, you get an infinite loop.
The name for a variable that keeps a running total is an accumulator, i.e. runningTotal += anotherNumber
The name for one loop execution is an iteration.
Sentinel - special value to stop loop
You can use a loop to make sure you have good input.

got_good_input = False

while got_good_input == False:

try:

x = int(input("Please enter a number: "))

got_good_input = True

except ValueError:

print("That was not a valid number. Try again...")

Explanation:

The input function returns a string so nothing could go wrong there.
The int function attempts to convert a string to an integer.
If the user enters an integer, like 2, this would work fine.
If the user enters something else, like two, this would not work and it would cause an exception.
An unhandled exception would cause the program to crash.
By putting that line of code that could cause an exception into a try statement, instead of the program crashing, program execution would jump from the line that caused the exception to the line that starts with except.
With this code, the only way it could get to the line where got_good_input is set to True would be if the line with int did not cause an exception.

Sample Program

# Prof. Vanselow

# An integration of everything I have learned about programming

print("Welcome to my Integration Project!")

continueProgram = True

while continueProgram:

print("Enter the choice for what you would like to see")

print("1. Area calculator")

print("2. Output formatting")

print("5. Quit")

userChoice = int(input())

if userChoice == 1:

# side is a variable

# a variable is a name for a location in memory

side = int(input("Enter the length of the side of a square to get the area:"))

area = side * side

print(area)

# You could also do print(side * side)

elif userChoice == 2:

print("Output can be formatted to two decimal places with format(variableName, '.2f')")

price = 599.9999

print("For example, 599.999 becomes:", format(price, '.2f'))

elif userChoice == 5:

continueProgram = False

else:

print("Invalid selection. Try again.")

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