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<font class="example">例7.1 </font>设A为一个10X20的数组，即n<span
class="down"><sub>1</sub></span>= 10 ,n<span class="down"><sub>2</sub></span>= 20。并设w＝4，数组第一个元素为A[1，1]
。则有（（low<span class="down"><sub>1</sub></span>*n<span class="down"><sub>2</sub></span>）＋low<span
class="down"><sub>2</sub></span>）*w=(1*20 ＋1）*4＝84。对赋值语句x：= A[y,z]的带注释的分析图7.10。该赋值语句在由底向上的分析中被翻译成如下三地址语句序列：
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t<span class="down"><sub>1</sub></span>：=
y*20 <br>
t<span class="down"><sub>1</sub></span>：=
t<span class="down"><sub>1</sub></span>＋z <br>
t<span class="down"><sub>2</sub></span>：=
A-84 <br>
t<span class="down"><sub>3</sub></span>:
= 4*t<span class="down"><sub>1</sub></span> <br>
t<span class="down"><sub>4</sub></span>：=
t<span class="down"><sub>2</sub></span>[t<span class="down"><sub>3</sub></span>] <br>
x : = t<span
class="down"><sub>4</sub></span> <br>
其中每个变量，我们用它的名字来代替<b>id</b>.place。
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<p>另外，要提到的是关于赋值语句中的类型转换问题。实际上,变量或常量的类型很多，编译器要么完全排斥混合类型的操作，要么生成适当的类型转换指令。一般说来允许类型的转换。例如，对于输入
<br>
x：＝y+i*j
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假定x和y为实数，i和j为整数，希望能有如下的输出： <br>
t<span class="down"><sub>1</sub></span> :＝i int*j（i与j作整数乘并赋给t<span
class="down"><sub>1</sub></span>） <br>
t<span class="down"><sub>3</sub></span> :＝inttoreal t<span
class="down"><sub>1</sub></span>（把t<span class="down"><sub>1</sub></span>由整型转换为实型并赋给t<span
class="down"><sub>3</sub></span>） <br>
t<span class="down"><sub>2</sub></span> :＝y real+t<span
class="down"><sub>3</sub></span> （y与t<span class="down"><sub>3</sub></span>
作实数加并赋给t<span class="down"><sub>2</sub></span>) <br>
x :＝t<span class="down"><sub>2</sub></span> <br>
可以想象的到，当包含大量的类型时，语义动作中因类型转换而需要区别的情形很多。因而，慎重的组织语义规则是重要且复杂的一项工作。
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<td><font class="yanshi"> 观看演示 </font></td>
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onclick="javascript:open('applets/test7_4/Page1.htm','_blank','menu=no,toolbar=no,location=no,directories=no,status=no,scrollbars=yes,resizable=yes,copyhistory=no,left=100,top=100,width=920,height=650')">对数组元素的翻译</font></td>
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