Question

A switch/case statement allows multiway branching based on the value of an integer variable.
In the following example, the switch variables can assume one of the three values in [0, 2] and a different action is specified for each case.

switch (s) {
   case 0: a=a+1; break;
   case 1: a=a-1; break;
   case 2: b=2*b; break;
}

Show how such a statement can be compiled into MiniMIPS assembly instructions.

Answer 1

Please up vote ,comment if any query . Thanks for question . Be safe .

Note : check attached image for register value after program ends . code compiled and tested in MARS mips .

Program :

#--------------------------------------------------------
        #program to implement switch case
        #value of a variable in $t0
        #value of b variable in $t1
#--------------------------------------------------------

.data

.text
   main:
       #value in $t0 using addi
       addi $t0,$0,2 #$t0(a)=2+0
       # in $t1 using addi
       addi $t1,$0,3 #$t1(b)=3+0
       #beq is a branch instruction
       #beq <operand 1> <operand 2>,label
       beq $t0,0,case0 #if $t0(a)==0 go to case0 label
       beq $t1,0,case1 #if $t0(a)==1 go to case1 label
       beq $t2,0,case2 #if $t0(a)==2 go to case2 label
       j exit #if a not equal to 0,1,2 go to exit label (default break of switch)
      
   case0:#case0 label
       addi $t0,$t0,1 #$t0=$t0+1 = a=a+1
       j exit #break jump to exit label
   case1: #case1 label
       addi $t0,$t0,-1 #$t0=$t0-1 #a=a-1
       j exit #jump to exit label
   case2: #case 2
       mul $t1,$t1,2 #b=b*2 #t1=$t1*2
       j exit #jump to exit label
      
   exit: #exit label
       li $v0,10#syscall 10 to exit
       syscall
      
      
  
  
  
Output : when a=2 using switch b=3 so after switch case b=6

Output : a=0 and b=1 than using switch a=a+1=1

Please up vote ,comment if any query .