ProgramGuru

Choose Data Types

Choose Data Types

An int represents whole numbers; double can represent fractional values; bool represents a logical result.

The operand types determine how a calculation happens before its result is assigned.

Before this lesson, review Name and Update Values when needed.

What you’ll learn

  • Use data types to choose Data Types.
  • Explain how the complete example produces 72.5.
  • Make the practice change and explain why the result changes or stays the same.

Follow a complete C++ example

The operand types determine how a calculation happens before its result is assigned.

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 total = 145;
  double average = total / 2.0;
  std::cout << average << '\n';
  return 0;
}

Expected output

72.5
Run in C++ compiler →

Connect the code to its result

C++17 · source used in this explanation

#include <iostream>

int main()  {
  int total = 145;
  double average = total / 2.0;
  std::cout << average << '\n';
  return 0;
}

Expected output

72.5

An int represents whole numbers; double can represent fractional values; bool represents a logical result. The operand types determine how a calculation happens before its result is assigned.

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

Important mistakes and boundaries

145 / 2 performs integer division even when stored in double. Floating-point values have finite precision and are not exact decimal-money storage.

Change the school example

C++17 · edit this complete example

#include <iostream>

int main()  {
  int total = 145;
  double average = total / 2.0;
  std::cout << average << '\n';
  return 0;
}

Your task: Change total to 151. 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: Change total to 151. The average becomes 75.5.

An int represents whole numbers; double can represent fractional values; bool represents a logical result. The operand types determine how a calculation happens before its result is assigned.

145 / 2 performs integer division even when stored in double. Floating-point values have finite precision and are not exact decimal-money storage.

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 total = 151;
  double average = total / 2.0;
  std::cout << average << '\n';
  return 0;
}

Expected output

75.5
Run in C++ compiler →

Check your understanding

C++17 · original program for this question

#include <iostream>

int main()  {
  int total = 145;
  double average = total / 2.0;
  std::cout << average << '\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

72.5

An int represents whole numbers; double can represent fractional values; bool represents a logical result. The operand types determine how a calculation happens before its result is assigned. 145 / 2 performs integer division even when stored in double. Floating-point values have finite precision and are not exact decimal-money storage.

Check a common mistake

What happens in double average = 145 / 2;?
Choose one answer. You can try again.

Answer and explanation

Integer division produces 72, then conversion stores 72.0.

Operand types select integer division; a widening assignment afterward cannot recover the discarded fraction.

What to remember

An int represents whole numbers; double can represent fractional values; bool represents a logical result. 145 / 2 performs integer division even when stored in double. Floating-point values have finite precision and are not exact decimal-money storage.

Useful connections: Name and Update Values, 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: Protect Fixed Values →