C++ double Keyword

The double keyword in C++ is used to declare variables of type double-precision floating-point. It is a built-in data type that can store decimal numbers with greater precision and a wider range compared to the float type. The double type is commonly used in scientific calculations and when higher precision is required for numeric data.

The size of a double typically depends on the system and compiler but is generally 8 bytes (64 bits) on most modern systems.

Syntax

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double variable_name = value;
double
The keyword that specifies a double-precision floating-point variable.
variable_name
The name of the variable being declared.
value
An optional initial value for the variable. It can be a decimal number or integer.

Examples

Example 1: Declaring and Initializing a double Variable

In this example, we will learn how to declare and initialize a double variable.

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#include <iostream>
using namespace std;

int main() {
    double pi = 3.14159; // Declare and initialize a double variable
    cout << "Value of pi: " << pi << endl;
    return 0;
}

Output:

Value of pi: 3.14159

Explanation:

  1. The variable pi is declared with the type double and initialized to the value 3.14159.
  2. The cout statement prints the value of pi to the console.

Example 2: Performing Arithmetic with double Variables

In this example, we will learn how to do arithmetic operations using double variables.

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#include <iostream>
using namespace std;

int main() {
    double num1 = 5.5, num2 = 2.2;

    double sum = num1 + num2;
    double product = num1 * num2;

    cout << "Sum: " << sum << endl;
    cout << "Product: " << product << endl;

    return 0;
}

Output:

Sum: 7.7
Product: 12.1

Explanation:

  1. The variables num1 and num2 are declared and initialized with decimal values.
  2. Arithmetic operations are performed, and the results are stored in sum and product.
  3. The results are printed using cout.

Example 3: Comparing Precision of double and float

In this example, we will show the precision difference between float and double types.

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#include <iostream>
#include <iomanip> // For std::setprecision
using namespace std;

int main() {
    float floatVal = 3.14159265358979323846f; // Single-precision floating-point
    double doubleVal = 3.14159265358979323846; // Double-precision floating-point

    cout << fixed << setprecision(20);
    cout << "Float value: " << floatVal << endl;
    cout << "Double value: " << doubleVal << endl;

    return 0;
}

Output:

Float value: 3.14159274101257324219
Double value: 3.14159265358979311600

Explanation:

  1. The float type has less precision, so its representation deviates after 6-7 decimal places.
  2. The double type has higher precision, accurately representing values up to 15-16 decimal places.
  3. The output shows the difference in precision between the two types.

Key Points about double Keyword

  1. The double keyword is used to declare double-precision floating-point variables.
  2. A double variable typically occupies 8 bytes (64 bits) in memory.
  3. The precision of double is higher than that of float, making it suitable for scientific calculations.
  4. The range of double is much wider, allowing it to store very large or very small values.
  5. Use the double type when precision and accuracy are critical.