C# - Math.Round()

Math.Round() function in C#

The Math.Round method in C# is used to round a decimal or double value to the nearest integral or specified number of fractional digits. Here's a detailed look at how to use Math.Round with various examples:

Basic Rounding to the Nearest Integral Value

By default, Math.Round rounds a number to the nearest integral value.

double value1 = 123.456;
double rounded1 = Math.Round(value1); // 123

double value2 = 123.556;
double rounded2 = Math.Round(value2); // 124

double value3 = 123.5;
double rounded3 = Math.Round(value3); // 124

double value4 = 123.4;
double rounded4 = Math.Round(value4); // 123

Console.WriteLine($"Rounded value1: {rounded1}"); // 123
Console.WriteLine($"Rounded value2: {rounded2}"); // 124
Console.WriteLine($"Rounded value3: {rounded3}"); // 124
Console.WriteLine($"Rounded value4: {rounded4}"); // 123

Floor and Ceiling

double floorValue = Math.Floor(123.456); // 123.0
double ceilingValue = Math.Ceiling(123.456); // 124.0

Truncate

double truncatedValue = Math.Truncate(123.456); // 123.0

Constants

The Math class provides several mathematical constants.

Pi and E

double pi = Math.PI; // 3.141592653589793
double e = Math.E; // 2.718281828459045

Rounding to a Specific Number of Decimal Places

we can specify the number of decimal places to round to by providing a second argument to Math.Round.

double value1 = 123.456789;
double rounded1 = Math.Round(value1, 2); // 123.46
double rounded2 = Math.Round(value1, 3); // 123.457

Console.WriteLine($"Rounded value1 to 2 decimal places: {rounded1}"); // 123.46
Console.WriteLine($"Rounded value1 to 3 decimal places: {rounded2}"); // 123.457

Examples with Different Decimal Places and Rounding Modes

Example 1: Rounding to 2 Decimal Places

double value1 = 123.456;
double rounded1 = Math.Round(value1, 2); // 123.46
double rounded2 = Math.Round(value1, 2, MidpointRounding.AwayFromZero); // 123.46

Console.WriteLine($"Rounded value1 to 2 decimal places: {rounded1}"); // 123.46
Console.WriteLine($"Rounded value1 to 2 decimal places (AwayFromZero): {rounded2}"); // 123.46

Example 2: Rounding to 0 Decimal Places

double value2 = 123.5;
double rounded3 = Math.Round(value2, 0); // 124 (Bankers' rounding)
double rounded4 = Math.Round(value2, 0, MidpointRounding.AwayFromZero); // 124

Console.WriteLine($"Rounded value2 to 0 decimal places: {rounded3}"); // 124
Console.WriteLine($"Rounded value2 to 0 decimal places (AwayFromZero): {rounded4}"); // 124

Example 3: Rounding Negative Numbers

double value3 = -123.5;
double rounded5 = Math.Round(value3, 0); // -124 (Bankers' rounding)
double rounded6 = Math.Round(value3, 0, MidpointRounding.AwayFromZero); // -124

Console.WriteLine($"Rounded value3 to 0 decimal places: {rounded5}"); // -124
Console.WriteLine($"Rounded value3 to 0 decimal places (AwayFromZero): {rounded6}"); // -124

Summary

The Math.Round method in C# is versatile and allows for various rounding options, whether you need to round to the nearest integer, a specific number of decimal places, or control how midpoint values are rounded. By understanding and using the Math.Round method effectively, you can ensure your numerical calculations meet the precision and rounding requirements of your application.