CSharp Basics FirstConsoleApp Input

C# Basics: First Console App and Simple Input

This lesson gives you a first experience with a C# console project and basic user input.

Related wiki pages:

• Overview: CSharpBible.md
• Basics of Console.WriteLine and DateTime: CSharp-Basics-ConsoleWriteLine-DateTime.md

Official docs:

• Get started with C#: https://learn.microsoft.com/dotnet/csharp/tour-of-csharp/

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1. Create your first console app

From a terminal:

dotnet new console -o MyFirstApp
cd MyFirstApp

The template creates a Program.cs with a Main method.

Replace Program.cs with:

using System;

namespace MyFirstApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello, C#!");
        }
    }
}

Run it:

dotnet run

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2. Basic types recap

• int – whole numbers
• string – text
• bool – true/false

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3. Read and validate user input

using System;

namespace MyFirstApp
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("Please enter your age: ");
            string? input = Console.ReadLine();

            if (!int.TryParse(input, out int age))
            {
                Console.WriteLine("Error: please enter a whole number.");
                return;
            }

            if (age >= 18)
            {
                Console.WriteLine("You are an adult.");
            }
            else
            {
                Console.WriteLine("You are not an adult.");
            }
        }
    }
}

This combines:

• Console.ReadLine for input
• int.TryParse for safe conversion
• if/else for basic branching

For more input/output patterns see Lesson20.12.2025.md (to be renamed to an I/O lesson file).

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4. Next steps

• Extend this program to be a simple calculator.
• Combine basic types from Lesson07.12.2025.md with input/output from this lesson.