C# Console Input and Output

Console Output Methods

Console.WriteLine()

Prints text and moves to a new line.

Console.WriteLine("Hello World!");
Console.WriteLine("This is on a new line");

Output:

Hello World!
This is on a new line

Console.Write()

Prints text without moving to a new line.

Console.Write("Hello ");
Console.Write("World!");

Output:

Hello World!

Combining Output

Console.Write("Enter your name: ");  // Prompt stays on same line
string sName = Console.ReadLine();

Console.WriteLine("Welcome, " + sName + "!");

Printing Special Characters

Escape Sequences

Escape Sequence	Description	Example
`\n`	New line	`"Line 1\nLine 2"`
`\t`	Tab	`"Name\tAge"`
`\\`	Backslash	`"C:\\Files"`
`\"`	Double quote	`"She said \"Hi\""`
`\'`	Single quote	`'It\'s'`

// New line
Console.WriteLine("Hello\nWorld");
// Output:
// Hello
// World

// Tab
Console.WriteLine("Name\tAge\tGrade");
Console.WriteLine("John\t20\tA");
// Output:
// Name    Age    Grade
// John    20     A

// Backslash
Console.WriteLine("File path: C:\\Users\\Documents");
// Output: File path: C:\Users\Documents

Verbatim Strings

Use @ to ignore escape sequences:

string sPath = @"C:\Users\Documents\file.txt";
Console.WriteLine(sPath);
// Output: C:\Users\Documents\file.txt

string sMultiLine = @"Line 1
Line 2
Line 3";
Console.WriteLine(sMultiLine);

ASCII Art Examples

Example 1: Duck (From Worksheet 1)

Console.WriteLine(" _");
Console.WriteLine(" ___(.)<");
Console.WriteLine(" \\____) ");
Console.WriteLine(" Duck");

Example 2: Butterfly (From Worksheet 1)

Console.WriteLine(" _ \" _ ");
Console.WriteLine(" (_\\|/_)");
Console.WriteLine(" (/|\\)");
Console.WriteLine(" Butterfly");

Example 3: Flower and Dog (From Practical Test 1)

Console.WriteLine(" _/)");
Console.WriteLine(" .-(_(=:");
Console.WriteLine(" | \\)");
Console.WriteLine(" (\\_ |");
Console.WriteLine(" :=)_)-| _/)");
Console.WriteLine(" (/ |-(_(=:");
Console.WriteLine(" | \\)");
Console.WriteLine(" ____|____");
Console.WriteLine(" [ ]");
Console.WriteLine(" \\ /");
Console.WriteLine(" \\ /");
Console.WriteLine(" \\___/");
Console.WriteLine("Flower.");

Console.WriteLine(" |");
Console.WriteLine(" .-. / \\");
Console.WriteLine(" ((\")) .|||.");
Console.WriteLine(" ==)-/_\\--o /| |\\");
Console.WriteLine(" /___\\ / | | \\");
Console.WriteLine("......d b....\\/\\|||/\\/........");

Console Input Methods

Console.ReadLine()

Reads a complete line of text (returns string).

Console.Write("Enter your name: ");
string sName = Console.ReadLine();
Console.WriteLine("Hello, " + sName + "!");

Console.ReadKey()

Reads a single key press (doesn't display in console by default).

Console.WriteLine("Press any key to continue...");
Console.ReadKey();  // Waits for any key press

Console.WriteLine("Press any key to exit...");
Console.ReadKey();

Console.Read()

Reads a single character as an ASCII value (integer).

Console.Write("Enter a character: ");
int iAsciiValue = Console.Read();
char ch = (char)iAsciiValue;
Console.WriteLine("You entered: " + ch);
Console.WriteLine("ASCII value: " + iAsciiValue);

Reading and Converting Input

Using Parse Methods

// Reading an integer
Console.Write("Enter your age: ");
int iAge = int.Parse(Console.ReadLine());

// Reading a double
Console.Write("Enter price: ");
double dPrice = double.Parse(Console.ReadLine());

// Reading a decimal
Console.Write("Enter salary: ");
decimal mSalary = decimal.Parse(Console.ReadLine());

// Reading a character
Console.Write("Enter grade (A-F): ");
char cGrade = char.Parse(Console.ReadLine());

Using Convert Class

Console.Write("Enter a number: ");
int iNumber = Convert.ToInt32(Console.ReadLine());

Console.Write("Enter temperature: ");
double dTemp = Convert.ToDouble(Console.ReadLine());

Formatting Output

String Concatenation

string sName = "Alice";
int iAge = 25;
Console.WriteLine("Name: " + sName + ", Age: " + iAge);

String.Format()

string sName = "Bob";
int iAge = 30;
double dScore = 85.75;

string sOutput = String.Format("Name: {0}, Age: {1}, Score: {2}", 
                                sName, iAge, dScore);
Console.WriteLine(sOutput);

// With formatting
string sFormatted = String.Format("Score: {0:0.00}", dScore);
Console.WriteLine(sFormatted);  // Score: 85.75

String Interpolation (Modern Way)

string sName = "Charlie";
int iAge = 28;
Console.WriteLine($"Name: {sName}, Age: {iAge}");

double dPrice = 19.99;
Console.WriteLine($"Price: R{dPrice:0.00}");

Number Formatting with ToString()

double dValue = 123.456789;

// Fixed decimal places
Console.WriteLine(dValue.ToString("0.00"));    // 123.46
Console.WriteLine(dValue.ToString("0.0"));     // 123.5
Console.WriteLine(dValue.ToString("F2"));      // 123.46
Console.WriteLine(dValue.ToString("F4"));      // 123.4560

// Currency
decimal mMoney = 1234.56m;
Console.WriteLine(mMoney.ToString("C"));       // R1,234.56

// Integer with leading zeros
int iNumber = 7;
Console.WriteLine(iNumber.ToString("00"));     // 07
Console.WriteLine(iNumber.ToString("000"));    // 007

Practical Examples from Course

Example 1: User Information

using System;

namespace UserInfo
{
    class Program
    {
        static void Main(string[] args)
        {
            // Get input
            Console.Write("Enter your name: ");
            string sName = Console.ReadLine();

            Console.Write("Enter your age: ");
            int iAge = int.Parse(Console.ReadLine());

            Console.Write("Enter your GPA: ");
            double dGPA = double.Parse(Console.ReadLine());

            // Display output
            Console.WriteLine("\n--- Student Information ---");
            Console.WriteLine("Name: " + sName);
            Console.WriteLine("Age: " + iAge);
            Console.WriteLine("GPA: " + dGPA.ToString("0.00"));

            Console.WriteLine("\nPress any key to exit...");
            Console.ReadKey();
        }
    }
}

Example 2: Stock Trading Calculator (Practical Test 2)

using System;

namespace StockTrading
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("EasyEquities: trading product of First World Trader (Pty) Ltd");
            Console.WriteLine("-------------------------------------------------------------");

            Console.Write("\nEnter trader's name: ");
            string sName = Console.ReadLine();

            Console.Write($"\nHow much did {sName} pay for the stock (1000 shares)? R");
            decimal mPurchaseAmount = decimal.Parse(Console.ReadLine());

            Console.Write($"What percentage (%) did {sName} pay his broker for the purchase? ");
            double dBuyingPercentage = double.Parse(Console.ReadLine()) / 100;

            Console.Write($"\nHow much did {sName} sell the stock (1000 shares) for? R");
            decimal mSellAmount = decimal.Parse(Console.ReadLine());

            Console.Write($"What percentage (%) did {sName} pay his broker for selling? ");
            double dSellingPercentage = double.Parse(Console.ReadLine()) / 100;

            // Calculate
            decimal mBrokerBuyingFee = mPurchaseAmount * (decimal)dBuyingPercentage;
            decimal mBrokerSellingFee = mSellAmount * (decimal)dSellingPercentage;
            decimal mFinalAmount = (mSellAmount - mBrokerSellingFee) - 
                                  (mPurchaseAmount + mBrokerBuyingFee);

            // Display
            Console.WriteLine($"\n{sName} made {mFinalAmount.ToString("C")} after the two transactions.");

            Console.WriteLine("\nPress any key to exit...");
            Console.ReadKey();
        }
    }
}

Example 3: Hexagon Area Calculator (Worksheet 2)

using System;

namespace HexagonArea
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("\nEnter the length of the side: ");
            double dLength = double.Parse(Console.ReadLine());

            double dHexagonArea = (3 * Math.Sqrt(3) / 2) * (dLength * dLength);

            Console.WriteLine("\nThe area of the hexagon is " + 
                            dHexagonArea.ToString("F4"));

            Console.WriteLine("\nPress any key to exit...");
            Console.ReadKey();
        }
    }
}

Example 4: Distance Between Two Points (Worksheet 2)

using System;

namespace DistanceCalculator
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("\nEnter x1: ");
            double dx1 = double.Parse(Console.ReadLine());

            Console.Write("Enter y1: ");
            double dy1 = double.Parse(Console.ReadLine());

            Console.Write("Enter x2: ");
            double dx2 = double.Parse(Console.ReadLine());

            Console.Write("Enter y2: ");
            double dy2 = double.Parse(Console.ReadLine());

            double dDistance = Math.Sqrt(Math.Pow(dx2 - dx1, 2) + 
                                        Math.Pow(dy2 - dy1, 2));

            Console.WriteLine("\nThe distance between the two points is " + 
                            dDistance.ToString("F2"));

            Console.WriteLine("\nPress any key to exit...");
            Console.ReadKey();
        }
    }
}

Using Math Class

The Math class provides mathematical functions:

// Square root
double dResult = Math.Sqrt(16);        // 4.0

// Power
double dPower = Math.Pow(2, 3);        // 8.0 (2³)
double dSquare = Math.Pow(5, 2);       // 25.0 (5²)

// Absolute value
double dAbs = Math.Abs(-10);           // 10.0

// Rounding
double dRound = Math.Round(3.7);       // 4.0
double dRound2 = Math.Round(3.4);      // 3.0

// Min and Max
int iMin = Math.Min(5, 10);            // 5
int iMax = Math.Max(5, 10);            // 10

// Constants
double dPi = Math.PI;                  // 3.14159...

Practice Exercises

Exercise 1: Personal Information

Create a program that asks for: - Name - Age - City - Favorite color

Display all information in a formatted way.

Exercise 2: Rectangle Calculator

Ask user for length and width. Calculate and display: - Area = length × width - Perimeter = 2(length + width)

Exercise 3: Temperature Display

Create a program that displays a temperature conversion table using proper formatting with tabs.

Common Mistakes to Avoid

❌ Forgetting to convert input:

string sAge = Console.ReadLine();
int iResult = sAge + 5;  // WRONG! Can't add string and int

✅ Correct:

int iAge = int.Parse(Console.ReadLine());
int iResult = iAge + 5;  // CORRECT

❌ Not handling special characters:

Console.WriteLine("C:\Users\file.txt");  // WRONG! \U and \f are escape sequences