# 變量 Go語言在聲明變量的時候，會自動對變量對應的內存區域進行初始化操作。每個變量會被初始化成其類型的默認值，例如： 整型和浮點型變量的默認值為0。 字符串變量的默認值為空字符串。 布爾型變量默認為`false`。 切片、函數、指針變量的默認為`nil`。 注意事項： ``` <pre class="calibre13">``` 函數外的每個語句都必須以關鍵字開始（<span class="token2">var</span>、<span class="token2">const</span>、func等） <span class="token1">:</span><span class="token">=</span>不能使用在函數外。 _多用于占位，表示忽略值。 ``` ``` ### iota `iota`是`go`語言的常量計數器，只能在常量的表達式中使用。`iota`在`const`關鍵字出現時將被重置為`0`。`const`中每新增一行常量聲明將使`iota`計數一次(`iota`可理解為`const`語句塊中的行索引)。 使用`iota`能簡化定義，在定義枚舉時很有用。 ``` <pre class="calibre13">``` <span class="token2">const</span> <span class="token1">(</span> n1 <span class="token">=</span> iota <span class="token6">//0</span> n2 <span class="token6">//1</span> n3 <span class="token6">//2</span> n4 <span class="token6">//3</span> <span class="token1">)</span> ``` ``` ### 幾個常見的iota示例: 使用\_跳過某些值 ``` <pre class="calibre13">``` <span class="token2">const</span> <span class="token1">(</span> n1 <span class="token">=</span> iota <span class="token6">//0</span> n2 <span class="token6">//1</span> _ n4 <span class="token6">//3</span> <span class="token1">)</span> ``` ``` `iota`聲明中間插隊 ``` <pre class="calibre13">``` <span class="token2">const</span> <span class="token1">(</span> n1 <span class="token">=</span> iota <span class="token6">//0</span> n2 <span class="token">=</span> <span class="token5">100</span> <span class="token6">//100</span> n3 <span class="token">=</span> iota <span class="token6">//2</span> n4 <span class="token6">//3</span> <span class="token1">)</span> <span class="token2">const</span> n5 <span class="token">=</span> iota <span class="token6">//0</span> ``` ``` ## 短變量聲明 ``` <pre class="calibre13">``` <span class="token2">package</span> main <span class="token2">import</span> <span class="token1">(</span> <span class="token4">"fmt"</span> <span class="token1">)</span> <span class="token6">// 全局變量m</span> <span class="token2">var</span> m <span class="token">=</span> <span class="token5">100</span> func <span class="token3">main</span><span class="token1">(</span><span class="token1">)</span> <span class="token1">{</span> n <span class="token1">:</span><span class="token">=</span> <span class="token5">10</span> m <span class="token1">:</span><span class="token">=</span> <span class="token5">200</span> <span class="token6">// 此處聲明局部變量m</span> fmt<span class="token1">.</span><span class="token3">Println</span><span class="token1">(</span>m<span class="token1">,</span> n<span class="token1">)</span> <span class="token1">}</span> ``` ``` ``` <pre class="calibre14">``` 函數外的每個語句都必須以關鍵字開始（<span class="token2">var</span>、<span class="token2">const</span>、func等） <span class="token1">:</span><span class="token">=</span>不能使用在函數外。 _多用于占位，表示忽略值。 ``` ```