How to convert/format numbers? (eg. 123K, 456M, 789B)

The maximum possible value for int is 2,147,483,647. You have to change int to long if you want to work with larger numbers. The maximum value for long is 9,223,372,036,854,775,807.

 using UnityEngine;
 using System.Collections.Generic;
 using System.Linq;
 
 public class Test : MonoBehaviour
 {
     void Start()
     {
         //Some tests
         Debug.Log("123000 is " + AbbrevationUtility.AbbreviateNumber(123000));
         Debug.Log("456000000 is " + AbbrevationUtility.AbbreviateNumber(456000000));
         Debug.Log("789000000000 is " + AbbrevationUtility.AbbreviateNumber(789000000000));
         Debug.Log("1000 is " + AbbrevationUtility.AbbreviateNumber(1000));
         Debug.Log("1000000 is " + AbbrevationUtility.AbbreviateNumber(1000000));
         Debug.Log("135000000000000 is " + AbbrevationUtility.AbbreviateNumber(135000000000000));
     }
 }
 
 public static class AbbrevationUtility
 {
     private static readonly SortedDictionary<long, string> abbrevations = new SortedDictionary<long, string>
     {
         {1000,"K"},
         {1000000, "M" },
         {1000000000, "B" },
         {1000000000000,"T"}
     };
 
     public static string AbbreviateNumber(float number)
     {
         for (int i = abbrevations.Count - 1; i >= 0; i--)
         {
             KeyValuePair<long, string> pair = abbrevations.ElementAt(i);
             if (Mathf.Abs(number) >= pair.Key)
             {
                 int roundedNumber = Mathf.FloorToInt(number / pair.Key);
                 return roundedNumber.ToString() + pair.Value;
             }
         }
         return number.ToString();
     }
 }

private static readonly SortedDictionary abbrevations = new SortedDictionary { {1000,"K"}, {1000000, "M" }, {1000000000, "B" } };

 public static string FormatK(float number)
 {
     for (int i = abbrevations.Count - 1; i >= 0; i--)
     {
         KeyValuePair<int, string> pair = abbrevations.ElementAt(i);
         if (Mathf.Abs(number) >= pair.Key)
         {

             float rest = number % pair.Key;
             float k = (number - rest) / pair.Key;
             float f = Mathf.Round(rest / (pair.Key / 10));
             string roundedNumber;
             if (f == 0)
             {
                 roundedNumber = k.ToString();
             }
             else
             {
                 if(f == 10)
                 {
                     f = 9;
                 }
                 roundedNumber = k.ToString() + "." + f.ToString();
             }

             return roundedNumber + pair.Value;
         }
     }
     return number.ToString();
 }