Read Statements and Comments
Read Statements and Comments
A statement performs a step, while a comment explains intent without performing that step.
Use braces to show which instructions belong to a function or decision.
Before this lesson, review Your First C++ Program when needed.
What you’ll learn
- Use syntax and comments to read Statements and Comments.
- Explain how the complete example produces 72.
- Make the practice change and explain why the result changes or stays the same.
Follow a complete C++ example
Use braces to show which instructions belong to a function or decision.
Read the declarations above main before tracing its statements. Each declared name supplies the value, type or operation used later. The std:: prefix selects a name from the standard library, and cout << sends a value to the output stream.
C++17 · main.cpp · complete program
#include <iostream>
int main() {
int marks = 72;
/* mark out of 100 */ std::cout << marks << '\n';
return 0;
}
Expected output
72Connect the code to its result
C++17 · source used in this explanation
#include <iostream>
int main() {
int marks = 72;
/* mark out of 100 */ std::cout << marks << '\n';
return 0;
}
Expected output
72A statement performs a step, while a comment explains intent without performing that step. Use braces to show which instructions belong to a function or decision.
Trace the result: Read the complete program below from its starting values to the output operations. Each std::cout statement displays the value supplied at that point; \n begins the next line. The resulting lines, in order, are 72. In this example, distinguish what the program calculates or changes from what it actually displays.
Important mistakes and boundaries
Comment markers inside a string are ordinary text. Comments should explain why a rule exists rather than contradicting the instructions.
Change the school example
C++17 · edit this complete example
#include <iostream>
int main() {
int marks = 72;
/* mark out of 100 */ std::cout << marks << '\n';
return 0;
}
Your task: Remove the comment. Before running your edited program, predict the new output and explain which stored value, condition or object changes. Keep the rest of the example intact.
Use the complete source repeated here; this task does not depend on remembering code from another section.
Worked answer and reasoning
Worked variation: Remove the comment. The program still prints 72.
A statement performs a step, while a comment explains intent without performing that step. Use braces to show which instructions belong to a function or decision.
Comment markers inside a string are ordinary text. Comments should explain why a rule exists rather than contradicting the instructions.
For a baseline run, save this source as main.cpp and use clang++ -std=c++17 -Wall -Wextra -pedantic main.cpp -o school, or equivalent g++ flags. Recompile after editing so that you run the updated executable.
The source and output below belong to the edited program. Compare them with the original example to see the consequence of this single change.
C++17 · worked variation · complete program
#include <iostream>
int main() {
int marks = 72;
std::cout << marks << '\n';
return 0;
}
Expected output
72Check your understanding
C++17 · original program for this question
#include <iostream>
int main() {
int marks = 72;
/* mark out of 100 */ std::cout << marks << '\n';
return 0;
}
What to remember
A statement performs a step, while a comment explains intent without performing that step. Comment markers inside a string are ordinary text. Comments should explain why a rule exists rather than contradicting the instructions.
Useful connections: Your First C++ Program, Give a Task a Name.
Language and design guidance: C++ Core Guidelines and C++ working draft. The draft describes an evolving language; these examples deliberately target C++17.
Reaching the recap and completing the quizzes are separate milestones.