Updates docs/EXPRESSION.md

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docs/EXPRESSION.md

@@ -51,6 +51,21 @@ The syntactic structure of if expression in UReport2 is shown in the figure belo
 
 # Case Expression
 
+Case expression is another form of conditional judgement provided by UReport2. It is similar to if judgement, but is simpler. Its syntactic structure is shown in the figure below:
+
+![](/docs/images/caseexpr.png)
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+The case judgement should be put in case\{...}, followed by several conditions and the return value.
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+| Examples of case expression | Note |
+| :--- | :--- |
+| case{A1==100 return "normal ", A1>100 and A1<1000 return "normal value", A1>100 and A1<1000 return 'high'} | The two conditions have different values returned |
+| case{A1==100 return "normal ", A1>100 and A1<1000 return "normal value", A1>100 and A1<1000  ‘high'} | There are also several options of the keyword of return in the case expression. |
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