C# Program to convert a Double to an Integer Value

To convert a double value to an integer value in C#, you can use several methods. The most common approach is using the Convert.ToInt32() method, which performs rounded conversion, or explicit casting for truncation.

The Int32 data type represents a 32-bit signed integer that can store values from -2,147,483,648 to 2,147,483,647.

Syntax

Following are the different syntaxes for converting double to integer −

// Using Convert.ToInt32() - rounds to nearest integer
int result = Convert.ToInt32(doubleValue);

// Using explicit casting - truncates decimal part
int result = (int)doubleValue;

// Using Math.Round() with casting - custom rounding
int result = (int)Math.Round(doubleValue);

Using Convert.ToInt32() Method

The Convert.ToInt32() method rounds the double value to the nearest integer using banker's rounding −

using System;

public class Demo {
    public static void Main() {
        double val1 = 21.34;
        double val2 = 21.67;
        double val3 = 21.5;
        
        int res1 = Convert.ToInt32(val1);
        int res2 = Convert.ToInt32(val2);
        int res3 = Convert.ToInt32(val3);
        
        Console.WriteLine("Converted double {0} to integer {1}", val1, res1);
        Console.WriteLine("Converted double {0} to integer {1}", val2, res2);
        Console.WriteLine("Converted double {0} to integer {1}", val3, res3);
    }
}

The output of the above code is −

Converted double 21.34 to integer 21
Converted double 21.67 to integer 22
Converted double 21.5 to integer 22

Using Explicit Casting

Explicit casting truncates the decimal part without rounding −

using System;

public class Demo {
    public static void Main() {
        double val1 = 21.34;
        double val2 = 21.99;
        double val3 = -15.78;
        
        int res1 = (int)val1;
        int res2 = (int)val2;
        int res3 = (int)val3;
        
        Console.WriteLine("Truncated double {0} to integer {1}", val1, res1);
        Console.WriteLine("Truncated double {0} to integer {1}", val2, res2);
        Console.WriteLine("Truncated double {0} to integer {1}", val3, res3);
    }
}

The output of the above code is −

Truncated double 21.34 to integer 21
Truncated double 21.99 to integer 21
Truncated double -15.78 to integer -15

Comparison of Conversion Methods

Using Math.Round() for Custom Rounding

using System;

public class Demo {
    public static void Main() {
        double val = 21.5;
        
        int roundUp = (int)Math.Round(val, MidpointRounding.AwayFromZero);
        int roundEven = (int)Math.Round(val, MidpointRounding.ToEven);
        
        Console.WriteLine("Original value: {0}", val);
        Console.WriteLine("Round away from zero: {0}", roundUp);
        Console.WriteLine("Round to even (banker's): {0}", roundEven);
    }
}

The output of the above code is −

Original value: 21.5
Round away from zero: 22
Round to even (banker's): 22

Conclusion

Converting double to integer in C# can be done using Convert.ToInt32() for rounded conversion or explicit casting (int) for truncation. Choose the method based on whether you need rounding or truncation behavior in your application.