How to retain the number of decimal places in C++

In C, retaining several decimal places usually involves formatting the output. This can be achieved by using std::setprecision and std::fixed from the I/O streams library. You can use std::cout and I/O stream formatting, std::stringstream, std::round or std::floor/std::ceil for rounding, and use the C-style printf function.

In C, retaining a few decimal places usually involves formatting the output, which can be done by using std from the I/O stream library: :setprecision and std::fixed to achieve this. The following are some ways to preserve the decimal places:

1. Use std::cout and I/O stream formatting

You You can use std::cout with std::fixed and std::setprecision to set the output format.

cpp

##

#include <iostream>  
#include <iomanip> // 包含 setprecision 和 fixed  
  
int main() {  
    double value = 3.141592653589793;  
    std::cout << std::fixed << std::setprecision(2) << value << std::endl; // 输出: 3.14  
    return 0;  
}

In this example, std::fixed makes sure to use fixed Point notation, and std::setprecision(2) sets the number of digits after the decimal point to 2.

2, Use std::stringstream

If you need to store the formatted string in a variable instead of outputting it directly To the console you can use std::stringstream.

cpp

##

#include <sstream>  
#include <iomanip>  
#include <string>  
  
int main() {  
    double value = 3.141592653589793;  
    std::stringstream ss;  
    ss << std::fixed << std::setprecision(2) << value;  
    std::string formatted_value = ss.str(); // formatted_value 现在包含 "3.14"  
    return 0;  
}

#include <cmath> // 包含 round 函数  
#include <iostream>  
  
int main() {  
    double value = 3.141592653589793;  
    double rounded_value = std::round(value * 100.0) / 100.0; // 四舍五入到小数点后两位  
    std::cout << rounded_value << std::endl; // 输出: 3.14  
    return 0;  
}

##

#include <cstdio>  
  
int main() {  
    double value = 3.141592653589793;  
    printf("%.2f\n", value); // 输出: 3.14  
    return 0;  
}

These methods can be used to retain several decimal places in C. Which method you choose depends on your specific needs and which programming style you prefer.

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