Check out example codes for "how print fload wiht 3 decimal in c++". It will help you in understanding the concepts better.

Code Example 1

#include <iostream>
#include <iomanip>

int main()
{
    double d = 122.345;

    std::cout << std::fixed;
    std::cout << std::setprecision(2);
    std::cout << d;
}

Code Example 2

#include <iostream>
#include <iomanip>

int main()
{
    double d = 122.345;
    std::cout << std::fixed << std::setprecision(2) << d;
}

//result that get print out: 122.34

Code Example 3

#include <iostream>
#include <cstdio>
using namespace std;

int main() 
{
    // This code helps you to print a number with desired decimal
    double Number=10.3454;
    printf("%.3lf",Number);

    return 0;
}

Code Example 4

std::cout << std::setprecision(2) << std::fixed;
// where the 2 is how many decimal places you want
// note you need to <iomanip>

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