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C++ Type Casting

Type casting is the change of a value from one type to another type. The static_cast tool writes the new type for the changed value.

A decimal becomes whole

static_cast<int> changes 9.99 to an int. The decimal part drops away, so the print shows 9.

#include <iostream>

int main() {
  std::cout << static_cast<int>(9.99) << "\n";
  return 0;
}

Two divisions

The cast makes 7 a double, so the first division keeps its decimal part. The second division uses whole numbers and drops the part.

#include <iostream>

int main() {
  std::cout << static_cast<double>(7) / 2 << "\n";
  std::cout << 7 / 2 << "\n";
  return 0;
}

A character code

Each character has a number code. A cast to int shows the code for the letter A.

#include <iostream>

int main() {
  std::cout << static_cast<int>('A') << "\n";
  return 0;
}

Text cannot become a number

This program tries to store text in an int variable. The compiler refuses the program and prints the error line below.

#include <iostream>

int main() {
  int count = "many";
  std::cout << count << "\n";
  return 0;
}

Example

#include <iostream>

int main() {
  int celsius = 25;
  double fahrenheit = static_cast<double>(celsius) * 9 / 5 + 32;
  std::cout << "Celsius: " << celsius << "\n";
  std::cout << "Fahrenheit: " << fahrenheit << "\n";
  return 0;
}

Key points

  • Use static_cast to change a value to a new type.
  • A cast to int drops the decimal part of a value.
  • A cast to double lets a division keep its decimal part.
  • Each character has a number code.
  • A cast of a char to int shows the number code of the character.
  • A cast cannot turn text into a number.

In this example, celsius holds the int value 25. The cast makes a double copy of that value for the formula. The formula gives 77, and the two lines print the Celsius and Fahrenheit values.

Note

A cast makes a changed copy. The original value keeps its own type.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Programiz C++ Compiler

Exercise

What does static_cast<int>(9.99) print?