C# Academy · Lesson

Implicit and Explicit Conversions

Convert between compatible types safely.

Lesson 3 of 413 steps

Implicit and Explicit Conversions is a free C# Academy lesson on CoddyKit. This is lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C# Academy learning path, and your progress syncs across the web and the CoddyKit app. The C# Academy course includes 4 lessons in total.

Converting Between Types

C# can convert one numeric type to another. Some conversions happen automatically (implicit), while others need an explicit cast.

using System;

class Program
{
    static void Main()
    {
        int i = 10;
        double d = i;       // implicit
        int back = (int)d;   // explicit
        Console.WriteLine(d + ", " + back);
    }
}

Implicit (Widening) Conversions

An implicit conversion is allowed when no data can be lost, such as int to long or int to double. No cast is needed.

using System;

class Program
{
    static void Main()
    {
        int i = 42;
        long l = i;      // widening, safe
        double d = i;    // widening, safe
        Console.WriteLine(l + ", " + d);
    }
}

Why Widening Is Safe

The target type can represent every value of the source type, so the compiler permits it silently.

using System;

class Program
{
    static void Main()
    {
        byte b = 200;
        int i = b;       // byte fits in int
        Console.WriteLine("byte " + b + " -> int " + i);
    }
}

Explicit (Narrowing) Conversions

An explicit conversion (a cast) is required when data might be lost, such as double to int. You write (int)value.

using System;

class Program
{
    static void Main()
    {
        double d = 9.78;
        int i = (int)d;   // truncates toward zero -> 9
        Console.WriteLine(i);
    }
}

Casting Truncates, Not Rounds

Casting a floating value to an integer drops the fractional part; it does not round. Use Math.Round first if you want rounding.

using System;

class Program
{
    static void Main()
    {
        double d = 7.99;
        Console.WriteLine("Cast: " + (int)d);
        Console.WriteLine("Round: " + (int)Math.Round(d));
    }
}

Overflow on Narrowing

If a value does not fit the target type, a plain cast may wrap around silently. Wrap it in checked to throw on overflow instead.

using System;

class Program
{
    static void Main()
    {
        int big = 300;
        byte wrapped = (byte)big;   // 300 wraps to 44
        Console.WriteLine("Wrapped: " + wrapped);

        try
        {
            byte safe = checked((byte)big);
            Console.WriteLine(safe);
        }
        catch (OverflowException)
        {
            Console.WriteLine("checked caught overflow");
        }
    }
}

Loss of Precision

Even some widening conversions, like very large long to float, can lose precision though they are still implicit.

using System;

class Program
{
    static void Main()
    {
        long big = 9007199254740993L;
        double approx = big;   // implicit, may lose precision
        Console.WriteLine("long: " + big);
        Console.WriteLine("double: " + approx.ToString("F0"));
    }
}

char and Numeric Conversions

A char implicitly converts to its numeric code, and you can explicitly cast a number back to a char.

using System;

class Program
{
    static void Main()
    {
        char c = 'A';
        int code = c;          // implicit -> 65
        char next = (char)(code + 1);   // explicit -> B
        Console.WriteLine(code + " -> " + next);
    }
}

Conversions in Expressions

In mixed arithmetic, smaller types are promoted to the larger type automatically before the operation.

using System;

class Program
{
    static void Main()
    {
        int a = 7;
        double b = 2;
        double result = a / b;   // a promoted to double -> 3.5
        Console.WriteLine(result);
    }
}

Integer Division Pitfall

If both operands are integers, division is integer division. Cast one to double first to get a fractional result.

using System;

class Program
{
    static void Main()
    {
        int a = 7, b = 2;
        Console.WriteLine("int / int: " + (a / b));
        Console.WriteLine("with cast: " + ((double)a / b));
    }
}

Putting It Together

Prefer implicit conversions when safe, use explicit casts when narrowing, and watch for truncation, overflow, and integer division.

using System;

class Program
{
    static void Main()
    {
        int total = 17, count = 5;
        double average = (double)total / count;   // cast to avoid integer division
        int rounded = (int)Math.Round(average);
        Console.WriteLine("avg=" + average + ", rounded=" + rounded);
    }
}

Quick Check

Test your understanding of conversions.

Answer it in the interactive lesson

Recap

Implicit (widening) conversions happen automatically when no data is lost (int to long, int to double). Explicit (narrowing) conversions need a cast like (int)x and may truncate or overflow. Use checked to catch overflow and cast to double to avoid integer division.

using System;

class Program
{
    static void Main()
    {
        double d = 3.9;
        int i = (int)d;     // explicit, truncates to 3
        long l = i;          // implicit widening
        Console.WriteLine(i + ", " + l);
    }
}

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Frequently Asked Questions

Is the “Implicit and Explicit Conversions” lesson free?

Yes — the full text of “Implicit and Explicit Conversions” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C# Academy course, upgrade to CoddyKit PRO. The C# Academy course includes 4 lessons in total.

What will I learn in “Implicit and Explicit Conversions”?

Convert between compatible types safely. You practise C# Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C# Academy?

No prior experience is required. C# Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 3 of 4.

How long does the “Implicit and Explicit Conversions” lesson take?

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