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Computers tend to be great at repetitive tasks. Further, repetitive tasks are relatively easy to program. You write code for the task once, then you place that task in a loop. A loop will try to repeat itself forever, but you usually don’t want that. So you write a control structure with a condition statement. Either the loop will run while the condition is true, or it will stop when the condition is true, depending on how the structure is written.

Below is a conditional loop statement. It will continue to increase the production until the step variable has reached the value of 10. The step +=1 increases the step variable by 1 each time this loop runs.

# Initialize variable
production = 1.0
step = 1

# Run loop
while(step < 10): # Condition statement
    production = production * 2.5
    print 'Production =', production
    step += 1

Activity

• Write and run the above program.
• Modify the program to run for exactly 30 steps.

Leveling Up

• Write a loop within a loop. This is a common programming practice. For example, the top level loop might run a calculation that occurs for each country, while the second level loop might run a calculation that occurs for each province to state.

Further Reading

• Python While Loops (W3schools)
• Python For Loops (W3schools)

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