Conditions and Loops

What you will be able to do

• Explain the five core programming decisions involved in conditions and loops.
• Choose a small code or command method that matches a stated input and output need.
• Interpret execution output and errors before changing broader system state.
• Apply an inspect, implement, test, verify, and recover workflow to a realistic automation task.

01

Build the Execution Model

Use conditions and loops with explicit predicates, finite progress, controlled exits, and visible final state.

Reliable automation separates input, representation, decision, action, output, and failure behavior. Before writing a longer script, state the exact starting data, the intended transformation, the observable result, and which state the program is permitted to change.

Use a disposable project and small deterministic samples. Run read-only inspection first, keep the interpreter or shell and working directory visible, and preserve the exact input with its output. A reproducible example is more useful than a large script whose state is unknown.

02

Boolean condition

A condition evaluates to a truth value that selects the next control-flow path. It is one distinct part of conditions and loops, so keep its input and output visible instead of hiding them inside a larger unexplained script.

Write the predicate in plain language and test true and false examples. Start with this small method: Evaluate the condition with two sample inputs. Record the code, interpreter or shell version, working directory, sample input, and visible result together.

The safety boundary is clear: Truthiness can differ from an explicit comparison. The expected evidence is The boolean condition result matches the documented input and expected state. If the result differs, keep the failure and reduce the example before changing unrelated code or system state.

03

Conditional branches

If and else branches separate mutually exclusive actions under one decision. It is one distinct part of conditions and loops, so keep its input and output visible instead of hiding them inside a larger unexplained script.

Keep the narrowest condition first and verify which branch ran. Start with this small method: Log the selected branch for a test input. Record the code, interpreter or shell version, working directory, sample input, and visible result together.

The safety boundary is clear: Overlapping conditions can make a later branch unreachable. The expected evidence is The conditional branches result matches the documented input and expected state. If the result differs, keep the failure and reduce the example before changing unrelated code or system state.

04

For iteration

A for loop processes each item from an iterable in a defined order. It is one distinct part of conditions and loops, so keep its input and output visible instead of hiding them inside a larger unexplained script.

Use a small collection and record the item and output for each iteration. Start with this small method: Loop over a three-item list. Record the code, interpreter or shell version, working directory, sample input, and visible result together.

The safety boundary is clear: Changing a collection while iterating can skip or repeat work. The expected evidence is The for iteration result matches the documented input and expected state. If the result differs, keep the failure and reduce the example before changing unrelated code or system state.

05

While progress

A while loop repeats while its condition remains true and needs a state change toward completion. It is one distinct part of conditions and loops, so keep its input and output visible instead of hiding them inside a larger unexplained script.

Identify the progress variable and test the stopping condition before automation. Start with this small method: Run with a strict small iteration limit. Record the code, interpreter or shell version, working directory, sample input, and visible result together.

The safety boundary is clear: A missing state change can create an infinite loop. The expected evidence is The while progress result matches the documented input and expected state. If the result differs, keep the failure and reduce the example before changing unrelated code or system state.

06

Loop exits

Break and continue alter normal loop flow for a documented exceptional condition. It is one distinct part of conditions and loops, so keep its input and output visible instead of hiding them inside a larger unexplained script.

Use an explicit exit reason and verify the final state after the loop. Start with this small method: Record the exit reason and processed count. Record the code, interpreter or shell version, working directory, sample input, and visible result together.

The safety boundary is clear: An early exit can leave partial work unexplained. The expected evidence is The loop exits result matches the documented input and expected state. If the result differs, keep the failure and reduce the example before changing unrelated code or system state.

07

Implement One Small Behavior

Translate the requirement into one input-output example before implementation. Name the target and side effects explicitly, validate input at the program boundary, and keep secrets and environment-specific configuration outside source code and ordinary logs.

Add the smallest code that makes the example work. Inspect intermediate values as structured data, not only formatted display text. When an operation can modify files, accounts, services, remote systems, or API resources, build a preview or disposable test path first.

Handle the expected failure that belongs to the operation. Preserve its type, message, target, and timing, then return a meaningful result or nonzero exit. Do not catch errors the program cannot explain merely to make the run appear successful.

08

Test and Handoff the Automation

Test a normal input, one boundary input, and one safe failure. Compare actual output with the written expectation and verify any changed state through an independent read-only query. A zero exit code or successful request is only part of the evidence.

Make the run reproducible. Record runtime version, dependencies, parameters, configuration source, sample data, output shape, and cleanup or reversal procedure. Remove temporary credentials, test files, sessions, and permissions after verification.

A useful handoff explains what the program accepts, what it returns or changes, how it reports failure, and where execution must stop for review. Escalate when authorization, data ownership, target scope, vendor contract, or safe recovery remains uncertain.

09

Recap Before Practice and Prove

Start with boolean condition. Write the predicate in plain language and test true and false examples. Verify that the boolean condition result matches the documented input and expected state.

Keep conditional branches explicit. Keep the narrowest condition first and verify which branch ran. Respect this boundary: overlapping conditions can make a later branch unreachable..

Use for iteration as a separate decision. Use a small collection and record the item and output for each iteration. Preserve the exact input and output.

Before expanding the script, review while progress. Identify the progress variable and test the stopping condition before automation. Stop when a missing state change can create an infinite loop..

Finish with loop exits. Use an explicit exit reason and verify the final state after the loop. Record the final result, failure behavior, cleanup, and reproducible next step.