<h3>Variables:</h3><ul><li><strong>Definition:</strong> Containers for storing data.</li><li><strong>Types:</strong><ul><li><strong>Immutable (val):</strong> Value cannot be changed after initialization.<pre class="!overflow-visible"><div class="contain-inline-size rounded-md border-[0.5px] border-token-border-medium relative bg-token-sidebar-surface-primary dark:bg-gray-950"><div class="overflow-y-auto p-4" dir="ltr"><code class="!whitespace-pre hljs language-kotlin"><span class="hljs-keyword">val</span> age = <span class="hljs-number">25</span>
</code></div></div></pre></li><li><strong>Mutable (var):</strong> Value can be updated.<pre class="!overflow-visible"><div class="contain-inline-size rounded-md border-[0.5px] border-token-border-medium relative bg-token-sidebar-surface-primary dark:bg-gray-950"><div class="overflow-y-auto p-4" dir="ltr"><code class="!whitespace-pre hljs language-kotlin"><span class="hljs-keyword">var</span> name = <span class="hljs-string">"John"</span>
</code></div></div></pre></li></ul></li></ul><h3>Data Types:</h3><ul><li><strong>Primitive Types:</strong><ul><li>Numeric: <code>Int</code>, <code>Double</code>, <code>Float</code>, <code>Long</code>, <code>Short</code>, <code>Byte</code></li><li>Characters: <code>Char</code></li><li>Boolean: <code>true</code>/<code>false</code></li></ul></li><li><strong>Collections:</strong> <code>Array</code>, <code>List</code>, <code>Set</code>, <code>Map</code></li><li><strong>Special Types:</strong><ul><li><code>String</code>: Text representation.</li><li><code>Any</code>: Parent of all types.</li></ul></li></ul><h3>Operators:</h3><ul><li><strong>Arithmetic:</strong> <code>+</code>, <code>-</code>, <code>*</code>, <code>/</code>, <code>%</code></li><li><strong>Relational:</strong> <code>==</code>, <code>!=</code>, <code>&lt;</code>, <code>&gt;</code>, <code>&lt;=</code>, <code>&gt;=</code></li><li><strong>Logical:</strong> <code>&amp;&amp;</code>, <code>||</code>, <code>!</code></li><li><strong>Assignment:</strong> <code>=</code>, <code>+=</code>, <code>-=</code>, <code>*=</code>, <code>/=</code></li><li><strong>Unary:</strong> <code>++</code>, <code>--</code></li></ul><h3>Example:</h3><pre class="!overflow-visible"><div class="contain-inline-size rounded-md border-[0.5px] border-token-border-medium relative bg-token-sidebar-surface-primary dark:bg-gray-950"><div class="sticky top-9 md:top-[5.75rem]"><div class="absolute bottom-0 right-2 flex h-9 items-center"><div class="flex items-center rounded bg-token-sidebar-surface-primary px-2 font-sans text-xs text-token-text-secondary dark:bg-token-main-surface-secondary"><span class="" data-state="closed"><button class="flex gap-1 items-center select-none py-1"><br></button></span></div></div></div><div class="overflow-y-auto p-4" dir="ltr"><code class="!whitespace-pre hljs language-kotlin"><span class="hljs-keyword">val</span> x: <span class="hljs-built_in">Int</span> = <span class="hljs-number">10</span>
<span class="hljs-keyword">val</span> y: <span class="hljs-built_in">Int</span> = <span class="hljs-number">20</span>
<span class="hljs-keyword">val</span> sum = x + y <span class="hljs-comment">// 30</span>
println(<span class="hljs-string">"Sum: <span class="hljs-variable">$sum</span>"</span>)
</code></div></div></pre><p>Understanding these basics lays the foundation for effective Android app development.</p>