Functions & Methods - C to C# | codemirr

Introduction

In this lesson, you'll learn about functions & methods in C#. Coming from C, you already have a foundation for understanding this concept. We'll build on that knowledge while highlighting the key differences.

Mirror Card

From C:

In C, you're familiar with defining reusable code.

In C#:

C# has its own approach to defining reusable code, which we'll explore step by step.

The C# Way

Let's see how C# handles this concept. Here's a typical example:

C# Example

using System;

// C# methods must belong to a class
static class MathUtils {
    public static int Add(int a, int b) => a + b;

    public static void Greet(string name) =>
        Console.WriteLine("Hello, " + name + "!");

    // out parameters (like C pointer params)
    public static void DivMod(int a, int b, out int q, out int r) {
        q = a / b;
        r = a % b;
    }

    // Func<T> replaces function pointers
    public static int Apply(Func<int, int, int> op, int a, int b) =>
        op(a, b);
}

MathUtils.DivMod(17, 5, out int q, out int rem);
Console.WriteLine(string.Format("{0} rem {1}", q, rem));
int result = MathUtils.Apply((a, b) => a + b, 3, 4);

Comparing to C

Here's how you might have written similar code in C:

C (What you know)

#include <stdio.h>

/* All functions are free-standing */
int add(int a, int b) {
    return a + b;
}

void greet(const char *name) {
    printf("Hello, %s!\n", name);
}

/* Multiple outputs via pointer params */
void divmod(int a, int b, int *q, int *r) {
    *q = a / b;
    *r = a % b;
}

/* Function pointer */
typedef int (*BinaryOp)(int, int);

int apply(BinaryOp op, int a, int b) {
    return op(a, b);
}

Mirror Card

From C:

You may be used to different syntax or behavior.

In C#:

C# methods must live inside a class; C functions are free-standing

Mirror Card

From C:

You may be used to different syntax or behavior.

In C#:

C# out parameters replace C's output pointer params

Mirror Card

From C:

You may be used to different syntax or behavior.

In C#:

C# Func<T> and lambda expressions replace C function pointers

Mirror Card

From C:

You may be used to different syntax or behavior.

In C#:

C# static class groups related functions like a C module

Step-by-Step Breakdown

1. Methods in Classes

C# has no free-standing functions — all code lives in classes. Use static classes to group utility functions like C source files.

int add(int a, int b) { return a + b; }

static class MathUtils {
    public static int Add(int a, int b) => a + b;
}

2. out Parameters

C# out parameters replace C's output pointer params, with type safety and without needing to pass addresses.

void divmod(int a, int b, int *q, int *r) { *q = a/b; *r = a%b; }

void DivMod(int a, int b, out int q, out int r) { q = a/b; r = a%b; }
// call: DivMod(17, 5, out int q, out int r);

3. Func and Lambdas

C# Func<in, out> and lambda expressions replace C function pointer typedefs with type-safe, concise alternatives.

typedef int (*BinaryOp)(int, int);

Func<int, int, int> op = (a, b) => a + b;
int result = op(3, 4);

Common Mistakes

When coming from C, developers often make these mistakes:

C# methods must live inside a class; C functions are free-standing
C# out parameters replace C's output pointer params
C# Func<T> and lambda expressions replace C function pointers

Common Pitfall

Don't assume C# works exactly like C. While the concepts may be similar, the syntax and behavior can differ significantly.

Key Takeaways

All C# code lives in classes; use static for utility functions
out parameters replace output pointer params
Func<T> + lambdas replace function pointers
Expression-bodied members (=>) for concise methods

Rule of Thumb

The best way to learn is by doing. Try rewriting some of your C code in C# to practice these concepts.

Introduction

Mirror Card

From C:

In C, you're familiar with defining reusable code.

In C#:

C# has its own approach to defining reusable code, which we'll explore step by step.

The C# Way

Let's see how C# handles this concept. Here's a typical example:

C# Example

using System;

// C# methods must belong to a class
static class MathUtils {
    public static int Add(int a, int b) => a + b;

    public static void Greet(string name) =>
        Console.WriteLine("Hello, " + name + "!");

    // out parameters (like C pointer params)
    public static void DivMod(int a, int b, out int q, out int r) {
        q = a / b;
        r = a % b;
    }

    // Func<T> replaces function pointers
    public static int Apply(Func<int, int, int> op, int a, int b) =>
        op(a, b);
}

MathUtils.DivMod(17, 5, out int q, out int rem);
Console.WriteLine(string.Format("{0} rem {1}", q, rem));
int result = MathUtils.Apply((a, b) => a + b, 3, 4);

Comparing to C

Here's how you might have written similar code in C:

C (What you know)

#include <stdio.h>

/* All functions are free-standing */
int add(int a, int b) {
    return a + b;
}

void greet(const char *name) {
    printf("Hello, %s!\n", name);
}

/* Multiple outputs via pointer params */
void divmod(int a, int b, int *q, int *r) {
    *q = a / b;
    *r = a % b;
}

/* Function pointer */
typedef int (*BinaryOp)(int, int);

int apply(BinaryOp op, int a, int b) {
    return op(a, b);
}

Mirror Card

From C:

You may be used to different syntax or behavior.

In C#:

C# methods must live inside a class; C functions are free-standing

Mirror Card

From C:

You may be used to different syntax or behavior.

In C#:

C# out parameters replace C's output pointer params

Mirror Card

From C:

You may be used to different syntax or behavior.

In C#:

C# Func<T> and lambda expressions replace C function pointers

Mirror Card

From C:

You may be used to different syntax or behavior.

In C#:

C# static class groups related functions like a C module

Step-by-Step Breakdown

1. Methods in Classes

C# has no free-standing functions — all code lives in classes. Use static classes to group utility functions like C source files.

int add(int a, int b) { return a + b; }

static class MathUtils {
    public static int Add(int a, int b) => a + b;
}

2. out Parameters

C# out parameters replace C's output pointer params, with type safety and without needing to pass addresses.

void divmod(int a, int b, int *q, int *r) { *q = a/b; *r = a%b; }

void DivMod(int a, int b, out int q, out int r) { q = a/b; r = a%b; }
// call: DivMod(17, 5, out int q, out int r);

3. Func and Lambdas

C# Func<in, out> and lambda expressions replace C function pointer typedefs with type-safe, concise alternatives.

typedef int (*BinaryOp)(int, int);

Func<int, int, int> op = (a, b) => a + b;
int result = op(3, 4);

Common Mistakes

When coming from C, developers often make these mistakes:

C# methods must live inside a class; C functions are free-standing
C# out parameters replace C's output pointer params
C# Func<T> and lambda expressions replace C function pointers

Common Pitfall

Don't assume C# works exactly like C. While the concepts may be similar, the syntax and behavior can differ significantly.

Key Takeaways

All C# code lives in classes; use static for utility functions
out parameters replace output pointer params
Func<T> + lambdas replace function pointers
Expression-bodied members (=>) for concise methods

Rule of Thumb

The best way to learn is by doing. Try rewriting some of your C code in C# to practice these concepts.