February 29, 2028 is the next leap day. A leap year program in C# needs one call, DateTime.IsLeapYear(year), or one expression: (year % 4 == 0 && year % 100 != 0) || year % 400 == 0. In this tutorial, I’ll show the built-in method, the manual leap year program in C# with if/else, … Read more >>

5! is 5 x 4 x 3 x 2 x 1 = 120. A factorial program in C# starts a long at 1 and multiplies it by every number from 2 to n. For 0 and 1 the loop never runs, so you get 1. In this tutorial, I’ll cover the factorial program in C# … Read more >>

Need 1234567 to print as 1,234,567? To format a number with commas in C#, call number.ToString(“N0”) for whole numbers or ToString(“N2”) for two decimals, and pass an en-US culture so the separator doesn’t change from machine to machine. In this tutorial, I’ll cover each case I’ve hit in production code for C# format number with … Read more >>

Your sales report lists January first, but the dashboard wants the newest month on top. To reverse an array in C#, call Array.Reverse(arr). It flips the array in place in one line. In this tutorial, I’ll walk through eight ways to reverse an array in C#, from the built-in method to loops that skip Reverse() … Read more >>

Got a list of states and need to know whether “Texas” is in it? In C#, a string array contains check is one line: states.Contains(“Texas”) returns true or false. In this tutorial, I’ll walk you through every flavor of the C# string array contains question: exact match, ignore case, substring, StartsWith, wildcard, null elements, multiple … Read more >>

Interviewers love this one: turn “4815” into an int without calling int.Parse. To convert a string to int without Parse in C#, loop over the characters and build the number yourself: In this tutorial, I’ll write my own convert string to int without parse in C# routine, then add a sign, invalid-character checks and overflow … Read more >>

Seven divided by two is 3 in C#, not 3.5. That surprise is why a C# program to add two numbers, then subtract, multiply and divide them, deserves more than one line. The core is simple: add with + and store the result. In this tutorial, I’ll start with a C# program to add two … Read more >>

Need to turn “Albuquerque” into “euqreuqublA”? To reverse a string in C#, copy it with ToCharArray(), flip the copy with Array.Reverse(), and wrap it in new string(…). C# strings don’t have a built-in Reverse() method, so that three-step pattern is the standard answer. In this tutorial, I’ll cover seven ways to reverse a string in … Read more >>

Is 97 prime? A prime number program in C# answers that by trying divisors: return false below 2, return n == 2 for even numbers, then test odd divisors while i <= n / i. If none divides evenly, it’s prime. In this tutorial, I’ll grow one small PrimeTools class step by step, the way … Read more >>

To delete a folder in C#, call Directory.Delete(path, recursive: true). It removes the folder and every file and subfolder inside it. Drop the true and it only deletes an empty folder. In this tutorial, I’ll work through each C# delete folder case I’ve run into: empty and non-empty folders, missing paths, clearing a folder but … Read more >>