Output Streams

Formatting Floating-Point Numbers

How can I format numbers in scientific notation using C++ output streams?

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Formatting floating-point numbers in scientific notation using C++ output streams is straightforward with the help of manipulators like std::scientific and std::setprecision().

Using std::scientific

To format a number in scientific notation, you can use the std::scientific manipulator:

#include <iostream>

int main() {
  double pi = 3.141592653589793;
  std::cout << std::scientific << pi;  
}
3.141593e+00

This converts the number into scientific notation with a default precision.

Adjusting Precision

You can control the number of digits displayed after the decimal point using the std::setprecision() manipulator from the <iomanip> header:

#include <iostream>
#include <iomanip>

int main() {
  double pi = 3.141592653589793;
  std::cout << std::scientific
    << std::setprecision(3)
    << pi;  
}
3.142e+00

Here, std::setprecision(3) sets the precision to three digits after the decimal point.

Combining with Other Manipulators

You can combine std::scientific with other manipulators for more complex formatting. For example, if you want to set a fixed width for the output, you can use std::setw() and std::setfill():

#include <iostream>
#include <iomanip>

int main() {
  double pi = 3.141592653589793;
  std::cout << std::scientific
            << std::setprecision(2)
            << std::setw(15)
            << std::setfill('_')
            << pi; 
}
_______3.14e+00

Resetting to Default

To revert to the default floating-point notation, you can use std::defaultfloat:

#include <iostream>
#include <iomanip>

int main() {
  double pi = 3.141592653589793;
  std::cout << std::scientific << pi << '\n';    
  std::cout << std::defaultfloat << pi;  
}
3.141593e+00
3.14159

Understanding how to use these manipulators allows you to present floating-point numbers in the most appropriate format for your application.

Answers to questions are automatically generated and may not have been reviewed.

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