Loops

Fixed loop (for)

Before a fixed loop starts, the number of times it will run is stated.

The range function produces a sequence of values. The last value in the sequence is always one less than the stop value:

range(stop)  ## Starts from 0

range(start, stop)

range(start, stop, step)

Example 1 - Stop value

Display the numbers 0 to 9, ten numbers in total. The loop variable is counter and it holds the current value from the range function.

# Fixed loop: Stop value
for counter in range(10):

    # Display loop variable
    print(counter)

Example 2 - Start and stop values

Display the numbers 1 to 9.

# Fixed loop: Start, Stop values
for counter in range(1, 10):

    # Display loop variable
    print(counter)

Example 3 - Start, stop, and stop values

Display the odd numbers from 1 to 9.

# Fixed loop: Start, Stop, Step values
for counter in range(1, 10, 2):

    # Display loop variable
    print(counter)

Conditional loop (while)

Before a conditional loop starts, the number of times it will run is not stated.

It only runs if the comparison is True. Each time the code is completed the comparison is checked again. If it is still True the code is run again.

Example

# Get value from user and cast to integer
value = int(input("Enter a value: "))

# Check value
while value < 10:

    # True: do the following

    # Increment value
    value = value + 1

    # True: Display value
    print(value)