CompareTo

This method acts upon 2 values (like strings or numbers). It returns an int value. The returned value (-1, 1 or 0) tells us which of the 2 numbers is bigger.

When using CompareTo, we usually return directly the value of the method call. This enables us to easily implement comparisons for sorting in C#.

Input and output

A negative one indicates the first value is smaller. A positive one indicates the first value is bigger. And a zero indicates the two values are equal.

5.CompareTo(6) = -1      First int is smaller.
6.CompareTo(5) =  1      First int is larger.
5.CompareTo(5) =  0      Ints are equal.

An example

This program uses 3 int values. Next, the variables "ab", "ba", and "ca" contain the results of the ints "a", "b", and "c" compared to one another.

using System;

class Program
{
    static void Main()
    {
        const int a = 5;
        const int b = 6;
        const int c = 5;

        int ab = a.CompareTo(b);
        int ba = b.CompareTo(a);
        int ca = c.CompareTo(a);

        Console.WriteLine(ab);
        Console.WriteLine(ba);
        Console.WriteLine(ca);
    }
}
-1
1
0

Uses

The CompareTo method is most useful in implementing sorting routines. We use CompareTo when implementing IComparable, Comparison delegate target methods, and Comparisons with lambdas.

A summary

CompareTo provides a standard way to determine which of two numbers is larger. The result tells us if a number comparison is larger, smaller, or equal.