Learn D - 10 Code Examples & CST Typing Practice Test

D is a high-level, statically typed, compiled systems programming language combining C-like performance with modern features like garbage collection, functional programming, and meta-programming.

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D Counter and Theme Toggle D Simple Addition D Factorial D Fibonacci Sequence D Max of Two Numbers D Array Sum D Even Numbers Filter D Conditional Counter Increment D Resettable Counter D Theme Toggle Only

Learn D with Real Code Examples

Updated Nov 20, 2025

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Code Sample Descriptions

D Counter and Theme Toggle

import std.stdio;

int count = 0;
bool isDark = false;

void updateUI() {
    writeln("Counter: ", count);
    writeln("Theme: ", isDark ? "Dark" : "Light");
}

void increment() {
    count += 1;
    updateUI();
}

void decrement() {
    count -= 1;
    updateUI();
}

void reset() {
    count = 0;
    updateUI();
}

void toggleTheme() {
    isDark = !isDark;
    updateUI();
}

// Simulate actions
updateUI();
increment();
increment();
toggleTheme();
decrement();
reset();

Demonstrates a simple counter with theme toggling using D variables and console output.

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D Simple Addition

import std.stdio;
void main() {
    int a = 10;
    int b = 20;
    int sum = a + b;
    writeln("Sum: ", sum);
}

Adds two numbers and prints the result.

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D Factorial

import std.stdio;
int factorial(int n) {
    return n <= 1 ? 1 : n * factorial(n - 1);
}
void main() {
    writeln("Factorial 5: ", factorial(5));
}

Calculates factorial recursively.

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D Fibonacci Sequence

import std.stdio;
int fib(int n) {
    return n < 2 ? n : fib(n - 1) + fib(n - 2);
}
void main() {
    foreach(i; 0 .. 10)
        writeln(fib(i));
}

Generates first 10 Fibonacci numbers.

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D Max of Two Numbers

import std.stdio;
void main() {
    int a = 10, b = 20;
    int max = a > b ? a : b;
    writeln("Max: ", max);
}

Finds the maximum of two numbers.

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D Array Sum

import std.stdio;
void main() {
    int[] arr = [1,2,3,4,5];
    int sum = 0;
    foreach(x; arr)
        sum += x;
    writeln("Sum: ", sum);
}

Sums elements of an array.

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D Even Numbers Filter

import std.stdio;
void main() {
    int[] arr = [1,2,3,4,5];
    foreach(x; arr)
        if(x % 2 == 0)
        writeln(x);
}

Prints even numbers from an array.

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D Conditional Counter Increment

import std.stdio;
void main() {
    int count = 3;
    if(count < 5)
        count++;
    writeln("Count: ", count);
}

Increment counter only if less than 5.

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D Resettable Counter

import std.stdio;
void main() {
    int count = 0;
    count += 1;
    count += 1;
    writeln("Count: ", count);
    count = 0;
    writeln("Count: ", count);
}

Counter that increments and can be reset.

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D Theme Toggle Only

import std.stdio;
void main() {
    bool isDark = false;
    writeln("Theme: ", isDark ? "Dark" : "Light");
    isDark = !isDark;
    writeln("Theme: ", isDark ? "Dark" : "Light");
    isDark = !isDark;
    writeln("Theme: ", isDark ? "Dark" : "Light");
}

Toggles theme multiple times.

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Frequently Asked Questions about D

What is D?

D is a high-level, statically typed, compiled systems programming language combining C-like performance with modern features like garbage collection, functional programming, and meta-programming.

What are the primary use cases for D?

Systems programming and OS-level development. High-performance computing. Game engines and graphics programming. Financial and trading applications. Compile-time code generation and metaprogramming

What are the strengths of D?

High-performance native code. Clean modern syntax with C-style familiarity. Powerful compile-time metaprogramming. Versatile multi-paradigm language. Rich standard library with ranges and algorithms

What are the limitations of D?

Smaller community and ecosystem than C++ or Rust. Less industrial adoption for large-scale projects. Limited GUI library support. Garbage collector can be unpredictable in real-time systems. Interfacing with C++ can be complex

How can I practice D typing speed?

CodeSpeedTest offers 10+ real D code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.

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Code Sample Descriptions

D Counter and Theme Toggle

import std.stdio;

int count = 0;
bool isDark = false;

void updateUI() {
    writeln("Counter: ", count);
    writeln("Theme: ", isDark ? "Dark" : "Light");
}

void increment() {
    count += 1;
    updateUI();
}

void decrement() {
    count -= 1;
    updateUI();
}

void reset() {
    count = 0;
    updateUI();
}

void toggleTheme() {
    isDark = !isDark;
    updateUI();
}

// Simulate actions
updateUI();
increment();
increment();
toggleTheme();
decrement();
reset();

Demonstrates a simple counter with theme toggling using D variables and console output.

Let’s Try →

D Simple Addition

import std.stdio;
void main() {
    int a = 10;
    int b = 20;
    int sum = a + b;
    writeln("Sum: ", sum);
}

Adds two numbers and prints the result.

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D Factorial

import std.stdio;
int factorial(int n) {
    return n <= 1 ? 1 : n * factorial(n - 1);
}
void main() {
    writeln("Factorial 5: ", factorial(5));
}

Calculates factorial recursively.

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D Fibonacci Sequence

import std.stdio;
int fib(int n) {
    return n < 2 ? n : fib(n - 1) + fib(n - 2);
}
void main() {
    foreach(i; 0 .. 10)
        writeln(fib(i));
}

Generates first 10 Fibonacci numbers.

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D Max of Two Numbers

import std.stdio;
void main() {
    int a = 10, b = 20;
    int max = a > b ? a : b;
    writeln("Max: ", max);
}

Finds the maximum of two numbers.

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D Array Sum

import std.stdio;
void main() {
    int[] arr = [1,2,3,4,5];
    int sum = 0;
    foreach(x; arr)
        sum += x;
    writeln("Sum: ", sum);
}

Sums elements of an array.

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D Even Numbers Filter

import std.stdio;
void main() {
    int[] arr = [1,2,3,4,5];
    foreach(x; arr)
        if(x % 2 == 0)
        writeln(x);
}

Prints even numbers from an array.

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D Conditional Counter Increment

import std.stdio;
void main() {
    int count = 3;
    if(count < 5)
        count++;
    writeln("Count: ", count);
}

Increment counter only if less than 5.

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D Resettable Counter

import std.stdio;
void main() {
    int count = 0;
    count += 1;
    count += 1;
    writeln("Count: ", count);
    count = 0;
    writeln("Count: ", count);
}

Counter that increments and can be reset.

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D Theme Toggle Only

import std.stdio;
void main() {
    bool isDark = false;
    writeln("Theme: ", isDark ? "Dark" : "Light");
    isDark = !isDark;
    writeln("Theme: ", isDark ? "Dark" : "Light");
    isDark = !isDark;
    writeln("Theme: ", isDark ? "Dark" : "Light");
}

Toggles theme multiple times.

Let’s Try →

Frequently Asked Questions about D

What is D?

D is a high-level, statically typed, compiled systems programming language combining C-like performance with modern features like garbage collection, functional programming, and meta-programming.

What are the primary use cases for D?

Systems programming and OS-level development. High-performance computing. Game engines and graphics programming. Financial and trading applications. Compile-time code generation and metaprogramming

What are the strengths of D?

High-performance native code. Clean modern syntax with C-style familiarity. Powerful compile-time metaprogramming. Versatile multi-paradigm language. Rich standard library with ranges and algorithms

What are the limitations of D?

How can I practice D typing speed?

CodeSpeedTest offers 10+ real D code examples for typing practice. You can measure your WPM, track accuracy, and improve your coding speed with guided exercises.