I have never typed C++ code since I retired. In C++ language, when solving the problem about floating point type, I have encountered a similar situation before, but it seems that there is no card data, basically using a setprecision function to reserve a few significant digits AC. But this time I got stuck on a set of data when calculating the average of any five numbers, and the problem was as follows:

#include <iostream>
#include <iomanip>
#include <stdio.h>
using namespace std;
int main(a){
    float a,b,c,d,e;
    cin>>a>>b>>c>>d>>e;
    float ave = (a+b+c+d+e)*1.0/5;
    / / cout < < setiosflags (ios: : fixed) < < setprecision (2) < < ave * 1.0 < < endl;
    cout<<setprecision(2)<<ave*1.0<<endl;
    //printf("%.2f",ave);
    return 0;
}
/* * Problem: Enter five consecutive numbers, ranging from 0.00 to 2.00, and output their average value, reserving two decimal places. * * * /

/* Use case: 1.82 1.86 1.88 1.65 1.78 Output should be: 1.80 Your output is: 1.8 ** */
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Let’s take a look at this code from beginning to end.

#include

contains all of the C++ header files, so you may not remember many of the smaller ones.

The source code for bits/stdc++. H is as follows:

// C++ includes used for precompiling -*- C++ -*-

// Copyright (C) 2003-2014 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library. This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 3, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
3.1, as Published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
// <http://www.gnu.org/licenses/>.

/** @file stdc++.h * This is an implementation file for a precompiled header. */

/ / 17.4.1.2 Headers

// C
#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#if __cplusplus >= 201103L
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdalign>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#endif
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Include is an I/O flow control header file, similar to the formatted output file in C, just remember, some specific operators and functions can refer to the table below.

Floating-point numbers but one thing to keep in mind is that the significant digits of a floating-point number default to 6. You can use the setPrecision (n) operator to change the number of significant digits displayed. But there are two important pitfalls to be aware of:

• If the significant number is less than the number to display, setPrecision drops it
• The trailing zero will be omitted

What if we want to output the number of decimal places we want?

C++ defines an ios::fixed operator in the iostream header, which prints output data to the screen as a decimal point. So we can artificially control the output to keep the number of digits after the decimal point.

Setiosflags (ios::fixed) is a function defined in. This operator performs actions in the area specified by the argument. We pass in the argument ios::fixed, which specifies actions in the form of a decimal point. And move the number to the right of the decimal point as accurately as possible.

For example, let’s take the example above:

cout<<ave*1.0<<endl;                                                (1)
cout<<setprecision(2)<<ave*1.0<<endl;                               (2)
cout<<setiosflags(ios::fixed)<<ave*1.0<<endl;                       (3)
cout<<setiosflags(ios::fixed)<<setprecision(2)<<ave*1.0<<endl;      (4)
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From what has been described above, we can easily get the following results:

(1) = 1.798
(2) = 1.8
(3) = 1.798000
(4) = 1.80
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