Why Does `std::cout.precision()` Not Print Trailing Zeros By Default?

Understanding std::cout.precision() and Trailing Zeros

std::cout.precision() is a function used to control the number of decimal places displayed for floating-point values. However, in certain scenarios, trailing zeros may not be printed as expected.

Consider the following code snippet:

#include <iostream>
#include <stdlib.h>
int main()
{
  int a = 5;
  int b = 10;
  std::cout.precision(4);
  std::cout << (float)a / (float)b << "\n";
  return 0;
}

This code prints 0.5 instead of the expected 0.5000. This is not due to the original integer data types but rather a lack of trailing zero suppression by default.

To correctly display trailing zeros, the std::fixed manipulator must be used:

std::cout << std::fixed;
std::cout << std::setprecision(4);
std::cout << (float)a / (float)b << "\n";

With this addition, the code will now output 0.5000 as intended. The std::fixed manipulator specifies that the floating-point value should be formatted with a fixed number of decimal places, ensuring that trailing zeros are retained.

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