How do you round off decimal places in C++?

Question

I need help rounding off a float value to one decimal place.

I know setprecision(x) and cout << precision(x). Both of which work if I wanted to round the entire float, but I am only interested in rounding the decimals to the tenths place.

Solution 1

There's another solution which doesn't require casting to int:

#include <cmath>

y = floor(x * 10d) / 10d

Solution 2

#include <cmath>

int main() {
    float f1 = 3.14159f;
    float f2 = 3.49321f;
    std::cout << std::floor(f1 * 10 + 0.5) / 10 << std::endl; 
    std::cout << std::floor(f2 * 10 + 0.5) / 10 << std::endl;
    std::cout << std::round(f1 * 10) / 10 << std::endl; // C++11
    std::cout << std::round(f2 * 10) / 10 << std::endl; // C++11
}