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Reuse a Typed Calculation

Reuse a Typed Calculation

A function template describes a family of functions parameterized by type.

A simple larger-value helper can compare compatible integer or decimal marks without separate copied definitions.

Before this lesson, review Let Members Own Resources when needed.

What you’ll learn

  • Use function templates to reuse a Typed Calculation.
  • Explain how the complete example produces 80 → 80.5.
  • Make the practice change and explain why the result changes or stays the same.

Follow a complete C++ example

A simple larger-value helper can compare compatible integer or decimal marks without separate copied definitions.

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>

template<typename T> T larger(T first, T second)  {
  return first < second ? second : first;
}
int main()  {
  std::cout << larger(70, 80) << '\n' << larger(72.5, 80.5) << '\n';
  return 0;
}

Expected output

80
80.5
Run in C++ compiler →

Connect the code to its result

C++17 · source used in this explanation

#include <iostream>

template<typename T> T larger(T first, T second)  {
  return first < second ? second : first;
}
int main()  {
  std::cout << larger(70, 80) << '\n' << larger(72.5, 80.5) << '\n';
  return 0;
}

Expected output

80
80.5

A function template describes a family of functions parameterized by type. A simple larger-value helper can compare compatible integer or decimal marks without separate copied definitions.

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 80 → 80.5. In this example, distinguish what the program calculates or changes from what it actually displays.

Important mistakes and boundaries

Template arguments must support the operations used. Mixed argument types may fail deduction rather than choosing an arbitrary common type.

Change the school example

C++17 · edit this complete example

#include <iostream>

template<typename T> T larger(T first, T second)  {
  return first < second ? second : first;
}
int main()  {
  std::cout << larger(70, 80) << '\n' << larger(72.5, 80.5) << '\n';
  return 0;
}

Your task: Compare 60 and 75. 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: Compare 60 and 75. The integer result is 75.

A function template describes a family of functions parameterized by type. A simple larger-value helper can compare compatible integer or decimal marks without separate copied definitions.

Template arguments must support the operations used. Mixed argument types may fail deduction rather than choosing an arbitrary common type.

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>

template<typename T> T larger(T first, T second)  {
  return first < second ? second : first;
}
int main()  {
  std::cout << larger(60, 75) << '\n' << larger(72.5, 80.5) << '\n';
  return 0;
}

Expected output

75
80.5
Run in C++ compiler →

Check your understanding

C++17 · original program for this question

#include <iostream>

template<typename T> T larger(T first, T second)  {
  return first < second ? second : first;
}
int main()  {
  std::cout << larger(70, 80) << '\n' << larger(72.5, 80.5) << '\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

80 80.5

A function template describes a family of functions parameterized by type. A simple larger-value helper can compare compatible integer or decimal marks without separate copied definitions. Template arguments must support the operations used. Mixed argument types may fail deduction rather than choosing an arbitrary common type.

What to remember

A function template describes a family of functions parameterized by type. Template arguments must support the operations used. Mixed argument types may fail deduction rather than choosing an arbitrary common type.

Useful connections: Let Members Own Resources, 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.

    Next lesson: Reuse a Typed Container →