Why Doesn't `std::cout.precision()` Display Trailing Zeros as Expected?

Correct Usage of std::cout.precision() for Trailing Zero Display

The precision specified using std::cout.precision() determines the number of decimal places to be included when formatting a floating-point number. However, in some cases, trailing zeros may not be displayed 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 attempts to output the result of dividing two integers as a floating-point number with a precision of four decimal places. However, the output shows "0.5" instead of the expected "0.5000". This occurs because the integer data types are implicitly converted to floating-point when performing the division, but the precision has not been specifically applied to the integer-to-float conversion.

To correctly display trailing zeros, an additional manipulator, std::fixed, must be used with std::cout:

#include <iostream>
#include <stdlib.h>
#include <iomanip>

int main() {
  int a = 5;
  int b = 10;
  std::cout << std::fixed;
  std::cout << std::setprecision(4);
  std::cout << (float)a / (float)b << "\n";
  return 0;
}

The std::fixed manipulator instructs std::cout to output floating-point numbers in fixed-point notation, which includes trailing zeros. The std::setprecision(4) manipulator specifies that the output should have a precision of four decimal places.

By incorporating the std::fixed manipulator, the output of the code snippet now correctly displays trailing zeros, resulting in "0.5000" as expected.

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