Case Statements

Switch and case statement is available in a variety of languages. The syntax of case statement is as follows:

1.     switch E  
2.                 begin   
3.                              case V1: S1  
4.                              case V2: S2  
5.                              .  
6.                              .  
7.                              .  
8. case Vn-1: Sn-1  
9. default: Sn  
10.                 end  

The translation scheme for this shown below:

Code to evaluate E into T

1. goto TEST  
2.                 L1:         code for S1  
3.                               goto NEXT  
4.                 L2:         code for S2  
5.                               goto NEXT  
6.                               .  
7.                               .  
8.                               .  
9.                 Ln-1:      code for Sn-1  
10.                               goto NEXT  
11.                 Ln:         code for Sn  
12. goto NEXT  
13.                 TEST:      if T = V1 goto L1       
14.                                if T = V2goto L2  
15.                                .  
16.                                .  
17.                                .  
18.                                if T = Vn-1 goto Ln-1  
19.                                goto   
20. NEXT:  

• When switch keyword is seen then a new temporary T and two new labels test and next are generated.
• When the case keyword occurs then for each case keyword, a new label Li is created and entered into the symbol table. The value of Vi of each case constant and a pointer to this symbol-table entry are placed on a stack.