Use a field width of 20 : double output « Data Types « C++ Tutorial

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3. double output

#include <iostream>
#include <iomanip>

using namespace std;

int main()
{
  cout << "Default format: " << 123.123456789 << endl;

  cout << "Use a field width of 20:\n";
  cout << "|" << setw(20) << "Testing" << "|\n\n";
  cout << "Use a field width of 20 with left justification:\n";
  cout << "|" << setw(20) << left << "Testing" << "|\n\n";

  return 0;
}