ProgramGuru

Give a Task a Name

Give a Task a Name

A function groups reusable instructions behind a name, parameters and a return type.

A pass rule can be called from several reports instead of copying its threshold everywhere.

Before this lesson, review Visit Rows and Columns when needed.

What you’ll learn

  • Use functions to give a Task a Name.
  • Explain how the complete example produces true.
  • Make the practice change and explain why the result changes or stays the same.

Follow a complete C++ example

A pass rule can be called from several reports instead of copying its threshold everywhere.

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>

bool passed(int marks)  {
  return marks >= 50;
}
int main()  {
  std::cout << std::boolalpha << passed(72) << '\n';
  return 0;
}

Expected output

true
Run in C++ compiler →

Connect the code to its result

C++17 · source used in this explanation

#include <iostream>

bool passed(int marks)  {
  return marks >= 50;
}
int main()  {
  std::cout << std::boolalpha << passed(72) << '\n';
  return 0;
}

Expected output

true

A function groups reusable instructions behind a name, parameters and a return type. A pass rule can be called from several reports instead of copying its threshold everywhere.

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 true. In this example, distinguish what the program calculates or changes from what it actually displays.

Important mistakes and boundaries

The declaration must be visible before a call. A return value and text printed by a function are different results.

Change the school example

C++17 · edit this complete example

#include <iostream>

bool passed(int marks)  {
  return marks >= 50;
}
int main()  {
  std::cout << std::boolalpha << passed(72) << '\n';
  return 0;
}

Your task: Call passed(40) instead. 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: Call passed(40) instead. The returned decision is false.

A function groups reusable instructions behind a name, parameters and a return type. A pass rule can be called from several reports instead of copying its threshold everywhere.

The declaration must be visible before a call. A return value and text printed by a function are different results.

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>

bool passed(int marks)  {
  return marks >= 50;
}
int main()  {
  std::cout << std::boolalpha << passed(40) << '\n';
  return 0;
}

Expected output

false
Run in C++ compiler →

Check your understanding

C++17 · original program for this question

#include <iostream>

bool passed(int marks)  {
  return marks >= 50;
}
int main()  {
  std::cout << std::boolalpha << passed(72) << '\n';
  return 0;
}
Before making the practice edit, what does the original C++17 program print?
Choose one answer. You can try again.

Answer and explanation

true

A function groups reusable instructions behind a name, parameters and a return type. A pass rule can be called from several reports instead of copying its threshold everywhere. The declaration must be visible before a call. A return value and text printed by a function are different results.

What to remember

A function groups reusable instructions behind a name, parameters and a return type. The declaration must be visible before a call. A return value and text printed by a function are different results.

Useful connections: Visit Rows and Columns.

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.

    Next lesson: Pass Inputs and Return Results →