C++/Data Type/Double

Calculates the area of a circle based on a radius inputted by the user.

<source lang="cpp">

1. include <iostream>
2. include <cmath>

using namespace std; int main(void) {

  double radius, area;
  cout << "Enter radius of circle: ";
  cin >> radius;
  area = 3.14159 * pow(radius, 2);
  cout << "The area is " << area << endl;
  return 0;

}

 </source>

Circumference and area of a circle with radius 2.5

<source lang="cpp">

1. include <iostream>

using namespace std; const double pi = 3.141593; int main() {

  double area, circuit, radius = 1.5;
  area = pi * radius * radius;
  circuit = 2 * pi * radius;
  cout << "\nTo Evaluate a Circle\n" << endl;
  cout << "Radius:        " << radius    << endl
       << "Circumference: " << circuit   << endl
       << "Area:          " << area      << endl;
  return 0;

}

 </source>

Create a table of square roots and squares.

<source lang="cpp">

1. include <iostream>
2. include <cmath>

using namespace std; int main() {

 double x;
 cout.precision(4);
 cout << "      x   sqrt(x)     x^2\n\n";
 for(x = 2.0; x <= 20.0; x++) {
   cout.width(7);
   cout << x << "  ";
   cout.width(7);
   cout << sqrt(x) << "  ";
   cout.width(7);
   cout << x*x << "\n";
 }

 return 0;

}

 </source>

Define, input and output double

<source lang="cpp">

1. include <iostream>

using namespace std; int main() {

 double hours, wage;
 cout << "Enter hours worked: ";
 cin >> hours;
 cout << "Enter wage per hour: ";
 cin >> wage;
 cout << "Pay is: $" << wage * hours;
 return 0;

}

 </source>

double value cout format

<source lang="cpp">

1. include <iostream>

using namespace std; int main() {

  double x = 12.0;
  cout.precision(2);              // Precision 2
  cout << " By default:   " << x << endl;
  cout << " showpoint:  " << showpoint  << x << endl;
  cout << " fixed:      " << fixed      << x << endl;
  cout << " scientific: " << scientific << x << endl;
  return 0;

}

 </source>

Do while loop with double value type

<source lang="cpp">

1. include <iostream>

using namespace std; int main() {

 double feet;
 do {
    cout << "Enter feet (0 to quit): ";
    cin >> feet;
    
    cout << feet * 12 << " inches\n";
 } while (feet != 0.0);
 return 0;

}

 </source>

Get sin, cos and tan value of an angle in double

<source lang="cpp">

1. include <iostream>
2. include <cmath>

using namespace std; int main(){

   double angle, dsine,dcos,dtan;
   cout << "Please enter an angle in radians \n";
   cin >> angle;
   dcos =cos(angle);
   dsine =sin(angle);
   dtan =tan(angle);
   cout << " Your angles trigonometric functions are \n";
   cout << " Sine is " << dsine << "\n";
   cout << " Cosine is " << dcos << "\n";
   cout << " Tangent is " << dtan << "\n";
   return 0;

}

 </source>

Get the square root, power and log value of a double

<source lang="cpp">

1. include <iostream>
2. include <cmath>

using namespace std; int main() {

double number, dsqrt,dpow,dlog;
cout << "Please enter a number \n";
cin >> number;
dsqrt =sqrt(number);
dpow =pow(number,5);
dlog =log(number);
cout << " Math Example\n";
cout << " Square Root is " << dsqrt << "\n";
cout << " Raised to the fifth power is " << dpow << "\n";
cout << " Log is " << dlog << "\n";
return 0;

}

 </source>

long double: Formatting includes precision, width, alignment, and format of large numbers.

<source lang="cpp">

1. include <iostream>
2. include <iomanip>

using namespace std; int main(){

long double number,factorial;
number=1.0;
factorial=1.0;
cout.precision(0);           // no decimal point
cout.setf(ios::left);        // left justify numbers
cout.setf(ios::fixed);       // use fixed format
 
for(int i=0;i<25;i++) {
  factorial*=number;
  number=number+1.0;
  cout.width(30);            // width of 30 characters
  cout << factorial << endl;
}
return (0);

}

 </source>

long double: Formatting includes precision, width and fixed with default of right justification when printing.

<source lang="cpp">

1. include <iostream>
2. include <iomanip>

using namespace std; main( ) {

long double number,factorial;
number=1.0;
factorial=1.0;
cout.precision(0);           // no decimal place
cout.setf(ios::fixed);       // use fixed format
for(int i=0;i<25;i++) {
  factorial*=number;
  number=number+1.0;
  cout.width(30);            // width of 30 characters
  cout << factorial << endl;
}
return (0);

}

 </source>

Read double value from keyboard and save it to another value

<source lang="cpp">

1. include <iomanip>
2. include <ios>
3. include <iostream>
4. include <string>

using std::cin; using std::setprecision; using std::cout; using std::string; using std::endl; using std::streamsize; int main() {

 cout << "Please enter your first name: ";
 string name;
 cin >> name;
 cout << "Hello, " << name << "!" << endl;
 cout << "Please enter your midterm and final exam grades: ";
 double midterm, final;
 cin >> midterm >> final;
 cout << "Enter all your homework grades, " "followed by end-of-file: ";
 int count = 0;
 double sum = 0;
 double x;
 while (cin >> x) {
   ++count;
   sum += x;
 }
 streamsize prec = cout.precision();
 cout << "Your final grade is " << setprecision(3)
      << 0.2 * midterm + 0.4 * final + 0.4 * sum / count
      << setprecision(prec) << endl;
 return 0;

}

 </source>

Using atof: convert string to double

<source lang="cpp">

1. include <iostream>
2. include <stdlib.h>

using namespace std; int main() {

  double d = atof( "99.0" );
  cout << "The string \"99.0\" converted to double is "
       << d << "\nThe converted value divided by 2 is "
       << d / 2.0 << endl;
  return 0;

}

 </source>

Using strtod: convert string to double

<source lang="cpp">

1. include <iostream>
2. include <stdlib.h>

using namespace std; int main() {

  double d;
  char *string = "51.2% are admitted", *stringPtr;
  d = strtod( string, &stringPtr );
  cout << "The string \"" << string 
       << "\" is converted to the\ndouble value " << d 
       << " and the string \"" << stringPtr << "\"" << endl;
  return 0;

}

 </source>