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Floating-point types

Learn float, double and long double types.

Floating-point types

C++ has three floating-point types: float (single precision, ~7 digits), double (double precision, ~15 digits) and long double (extended, ~18+ digits).

When writing a float value, use the f suffix: float temp = 36.5f;. Without the suffix, 36.5 is a double.

For most calculations double is recommended; precision loss is small and there is no performance penalty on modern CPUs. Choose float when memory savings matter.

float and double precision

float holds about 7 significant digits; double about 15. So printing float x = 3.14159265f; may lose some digits.

In scientific and financial calculations, small errors accumulate; that is why double is the safe choice. Do not trust floating-point equality: 0.1 + 0.2 may not exactly equal 0.3.

You can control the number of printed digits with std::setprecision (from <iomanip>); you will see it at an advanced level.

Practice Print float and double

Inside main, declare a float (value 36.5f) and a double (value 3.14159265). Print both on separate lines with std::cout using std::endl.

Starter code

main.cpp
#include <iostream>

int main() {
    // Declare float and double
    // Print each with std::cout
    return 0;
}

Sample solution

main.cpp
#include <iostream>

int main() {
    // Declare float and double
    float temperature = 36.5f;
    double precise = 3.14159265;
    // Print each with std::cout
    std::cout << temperature << std::endl;
    std::cout << precise << std::endl;
    return 0;
}

Expected output

36.5
3.14159

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Double-precision variable

Question 
____ precise = 3.14159265;
Answer 
double precise = 3.14159265;

Explanation: double offers about 15 digits of precision.

2 Which is the highest-precision floating type?

  • int
  • float
  • double
  • long double Correct answer

Explanation: long double offers the widest precision.

3 Match floating types

Term Meaning
float ~7 digits
double ~15 digits
long double ~18+ digits
f suffix float marker

All lessons in Beginner

1 C++ basics

  1. What is C++?
  2. Your first program
  3. std::cout
  4. std::cin
  5. Comments
  6. Summary - C++ basics

2 Variables

  1. Declaring variables
  2. auto
  3. const
  4. constexpr
  5. Type conversion
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. bool and char
  4. std::string
  5. sizeof
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Bitwise operators
  6. Summary - Operators

6 Strings

  1. std::string basics
  2. String concatenation
  3. String length
  4. Substring
  5. String search
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. The switch statement
  4. The ternary operator
  5. Nested conditionals
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. Range-based for
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding products
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Arrays

  1. C-style arrays
  2. Array access
  3. std::array
  4. Multidimensional arrays
  5. Arrays and loops
  6. Summary - Arrays

11 std::vector

  1. Declaring vectors
  2. push_back
  3. size and at
  4. Vector access
  5. Vector loop
  6. Summary - std::vector

12 Functions

  1. Defining functions
  2. Return values
  3. Parameters
  4. Function overloading
  5. Default parameters
  6. Summary - Functions

13 References

  1. What is a reference?
  2. Declaring references
  3. Reference parameters
  4. const references
  5. Dangling references
  6. Summary - References

14 Pointer basics

  1. What is a pointer?
  2. The & address operator
  3. Pointer dereference
  4. nullptr
  5. Pointer arithmetic
  6. Summary - Pointer basics

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. String streams
  2. stoi and stod
  3. to_string
  4. String comparison
  5. String modification
  6. Summary - Advanced strings

17 Structs

  1. Defining structs
  2. Using structs
  3. Struct and function
  4. Array of structs
  5. Nested structs
  6. Summary - Structs

18 Exception basics

  1. try/catch
  2. throw
  3. std::exception
  4. Custom exceptions
  5. catch all
  6. Summary - Exceptions

19 Namespaces

  1. Defining namespaces
  2. using
  3. std namespace
  4. Nested namespaces
  5. Namespace alias
  6. Summary - Namespaces

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together