Introduction to CS | 3.3: While Loops, Counters, and Infinite Loops
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Learn to write Python while loops that respond to user input, track iterations with counter variables, and terminate cleanly. This video traces exactly how the loop condition is evaluated on each pass — and shows what goes wrong when the loop variable is never updated.
Key concepts covered:
• User-input while loops: reading and reassigning the loop variable inside the loop body to eventually make the condition false
• Memory traces showing how variable bindings change across iterations
• Case-sensitive string comparison: "RIGHT" does not equal "right" — and how .lower() fixes it
• Numeric while loops: decrementing a counter variable to control how many times the loop runs
• Step-by-step trace table for a loop counting down from n = 4 to n = 0, including five condition checks (four true, one false)
• Infinite loops: how a missing variable update causes endless repetition
• How to stop an infinite loop: Ctrl+C, closing the program, or interrupting the kernel
• The while True pattern as a guaranteed infinite loop
• Combining a counter variable with a conditional inside the loop body
• The not-equal operator (!=) for testing non-equivalence
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SOURCE MATERIALS
The source materials for this video are from • Lecture 3: Iteration