What is C++ Double data type?
- The double is among one of the available data types in C++ like float, int, char etc.
- 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:
double var;
double var, var2, var3;
double var = 500.987678767;
double var = -500.877878787;
double var = 500;
float var = 87; //Declaring a float type variable without suffix f or F is taken as double type as well.
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.
Note that, the output varies from compiler to compiler – where you execute this code:
#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;
}
You saw, the values for double and long double are displayed correctly with the 11 precision setting. However, the float is showing garbage value after 7.