How Can I Accurately Print Decimal Values to a Specific Precision in C ?

Printing Decimal Values Accurately with C Streams

When working with floating-point numbers in C , it's often necessary to control the number of decimal places displayed during output. By default, the standard output operator cout may not format numbers to the desired precision.

Solution Using

To specify the number of decimal places for floating-point output, use the std::fixed and std::setprecision manipulators from the header:

#include <iomanip>

std::cout << std::fixed;
std::cout << std::setprecision(2);
std::cout << d;

std::fixed sets the floating-point representation to fixed-point notation, and std::setprecision(2) specifies that two decimal places will be displayed.

Example Usage

Consider the following example:

double d = 122.345;

std::cout << std::fixed;
std::cout << std::setprecision(2);
std::cout << d;

This code will output:

122.34

Additional Notes:

• std::setprecision affects only the current output operation, not subsequent ones.
• If no precision is specified, std::setprecision uses the default precision determined by the implementation.
• Alternatively, std::scientific and std::showpoint manipulators can be used for scientific notation and displaying trailing zeros respectively.

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