Build a Practical How Programs Work Example in Programming Foundations

Define the build target

Write a parent program that starts a child process, captures the child output and exit code, and explains which parts belong to source code, runtime, operating system process creation, memory, CPU scheduling, and output.

Keep the How Programs Work build centered on these technical constraints: Source code is text written for people and language tooling; the CPU does not execute source text directly. A compiler can translate ahead of time while an interpreter or virtual machine can translate or execute instructions at runtime; many modern runtimes combine these approaches. Apply them through this path lens: Use language-neutral program state, control flow, runtime behavior, and terminal evidence so the concept transfers across languages. Use language-neutral program state, control flow, runtime behavior, and terminal evidence so the concept transfers across languages.

Implement the core behavior

Implement How Programs Work around the module artifact—an execution-chain diagram plus process/runtime evidence from a working and failing program—and keep the implementation specific to this path context: Use language-neutral program state, control flow, runtime behavior, and terminal evidence so the concept transfers across languages.

import os
import subprocess
import sys

child_code = "import os; print('child-pid:', os.getpid()); print('child-output: 42')"
result = subprocess.run([sys.executable, '-c', child_code], capture_output=True, text=True)
print('parent-pid:', os.getpid())
print(result.stdout.strip())
print('child-exit-code:', result.returncode)

python3 parent-child-process.py

Different parent/child process IDs, captured child output, and exit code 0.

practice/\n├── README.md\n├── parent-child-process.py\n└── evidence/\n    └── expected-result.txt

Run the complete path

Run one realistic How Programs Work case end to end and record the required evidence: interpreter path, process ID, exit code, terminal output/error, and a short explanation of where the failure occurred. Interpret the result through this path context: Use language-neutral program state, control flow, runtime behavior, and terminal evidence so the concept transfers across languages.

Change one meaningful condition

Modify one condition central to How Programs Work using this path context: Use language-neutral program state, control flow, runtime behavior, and terminal evidence so the concept transfers across languages. Predict the new result before rerunning the same workflow.

Verify the artifact

Your deliverable is an execution-chain diagram plus process/runtime evidence from a working and failing program.

Common mistakes to avoid

• Confusing storage with memory.
• Assuming source code executes directly.
• Mixing bits, bytes, and encoded values.
• Ignoring the operating system/runtime layer.