C++ Double [Declaration, Limits, size etc.]

What is C++ double data type?

• The double is among one of the available data types in C++ like float, int, char, etc.
• The double data type allows storing bigger floating point numbers (decimal numbers) than the float data type.
• It takes eight bytes (64 bits) in the memory whereas float takes four bytes.
• Generally, it’s precision is 15 digits.

How to declare a double variable in C++?

You may declare double variables in these ways:

C++ Program for declaring and using double type variables

In this C++ program, we will create a few double-type variables and display their values by using cout. Have a look:

#include<iostream>

using namespace std;

int main(){

// Declaring and assigning float variables

double d1 = 30.0;
double d2 = -30.5;
double d3 = 25.994524;
double d4 = 4E-6; //An Exponential Number

//Displaying Double variable values
 cout << "First Double Variable Value  = " << d1 << endl;

 cout << "Second Double Variable Value  = " << d2 << endl;

 cout << "Third Double Variable Value  = " << d3 << endl;
 cout << "Fourth Double Variable Value  = " << d4 << endl;

return 1;

}

Output:

Check the memory size of double variables example

As mentioned earlier, a double variable takes eight bytes in memory. The example below shows the actual size by using the sizeof() function.

See the program and its output below:

#include<iostream>

using namespace std;

int main(){

// Declaring and assigning float variables

double d1 = 30.0;
double d2 = -30.5;
double d3 = 25.994524;
double d4 = 4E-6; //An Exponential Number

//Displaying Double variable values

 cout << "First Double Variable Size  = " << sizeof(d1) << endl;
 cout << "Second Double Variable Size  = " << sizeof(d2) << endl;
 cout << "Third Double Variable Size  = " << sizeof(d3) << endl;
 cout << "Fourth Double Variable Size  = " << sizeof(d4) << endl;

return 1;

}

Output:

Checking the minimum and maximum limits of the double type variables example

The example below shows using the numeric_limits to check the minimum and maximum limits of the double-type variables. You have to include the <limits> in the header.

#include <iostream>

#include <limits>

using namespace std;

int main(){

   cout << "The Max and Min Double Limit:" << endl;
   cout << "min: " << numeric_limits<double>::min() << endl;
   cout << "max: " << numeric_limits<double>::max() << "\n\n";

   cout << "The Max and Min Float Limit:" << endl;

   cout << "min: " << numeric_limits<float>::min() << endl;

   cout << "max: " << numeric_limits<float>::max() << "\n\n";

   cout << "The Max and Min Long Double Limit:" << endl;

   cout << "min: " << numeric_limits<long double>::min() << endl;

   cout << "max: " << numeric_limits<long double>::max() << "\n\n";

return 1;

}

Output:

Checking and comparing the precision of double types

The following example checks the precision of double-type variables and compares it with other floating type data types like float and long double.

#include<iostream>
#include<cstdlib>

using namespace std;

int main(){

// Declaring and assigning floating types variables

double dbl1 = 50.8451425421425;

float flt1 = 5.8451425421425f;

long double ld1 = 5.8451425421425L;

//Displaying variable size
 cout << "Double Variable  = " << dbl1 << endl;
 cout << "Float Variable  = " << flt1 << endl;
 cout << "Long Double Variable  = " << ld1 << endl;

return 1;

}

Output:

Now let us use the setprecision() function and see the result

#include<iostream>
#include <iomanip>
#include<cstdlib>

using namespace std;

int main(){

// Declaring and assigning floating types variables

double dbl1 = 50.8451425421425;
float flt1 = 5.8451425421425f;
long double ld1 = 5.8451425421425L;

//Setting precision

cout << setprecision(11);

//Displaying variable size

 cout << "Double Variable  = " << dbl1 << endl;

 cout << "Float Variable  = " << flt1 << endl;
 cout << "Long Double Variable  = " << ld1 << endl;

return 1;

}

Result:

You saw the values for double and long double are displayed correctly with the 11 precision setting. However, the float is showing a garbage value after 7.