Question

Write an ARM program that implements a simple four-function calculator and prompts the user to enter a pair of decimal integers (A and B) followed by a character that specifies one of the operators:

‘+’ for addition to compute A+B                            

‘-‘ for subtraction to compute A-B

‘*’ for multiplication to produce the product A*B

‘/’ for division to produce the quotient A/B.

Input should be the pair of numbers followed by the operand followed by a return.

For example

5 5 + [enter]

Your program should display the result produced by performing the indicated operation on the two input operands A and B. Only the four operators listed above should be allowed and an attempt to divide by zero should be prohibited.

Define a separate function for each of the allowed operators and use the function names ADD, SUB, MUL, and DIV.

Upon return from the function, the main program should display the result on the console.

Please write the full code using scanf, switch statements, and subroutines to get the answer from the two inputs.

Answer 1

AREA   DisplayResult, CODE, READONLY
   IMPORT   main
   IMPORT   getkey
   IMPORT   sendchar
   EXPORT   start
   PRESERVE8

start

   MOV   R4, #0           ;   input1 = 0;
   MOV   R6, #10          ;   load value 10 into R6;
   MOV   R7, #0           ;   operator = 0;
   MOV   R8, #0           ;   input2 = 0;
  
while ;   while (boolean finished == false)
;   {
   BL   getkey ;      read key from console
   BL   sendchar ;         echo key back to console
  
   CMP   R0, #"+" ;        if (key=="+")
   BNE   elsif1 ;        {
   MOV   R7, #"+" ;           operator = "+";
   B   endwh ; finished = true;
;       }
elsif1
   CMP   R0, #"-" ;        else if (key=="-")
   BNE   elsif2 ;        {
   MOV   R7, #"-" ;           operator = "-"
   B   endwh ;            finished = true;
;       }
elsif2
   CMP   R0, #"*" ;        else if (key=="*")
   BNE   elsif3 ;        {
   MOV   R7, #"*" ;           operator = "*"
   B   endwh ;            finished = true;
;       }
elsif3 ;       else {
   SUB   R0, R0, #0x30 ;            convert ASCII to numeric value
   MUL   R4, R6, R4 ;            input1 = input1 x 10;
   ADD   R4, R0, R4 ;            input1 = input1 + value;
   B   while ;        }
endwh ;    )
  
while2
   BL   getkey ;    read key from console
   CMP   R0, #0x0D         ;   while (key != CR)
   BEQ   endwh2 ;   {
   BL   sendchar ;       echo key back to console
   SUB   R0, R0, #0x30 ;       convert ASCII to numeric value
   MUL   R8, R6, R8 ;       input2 = input2 x 10;
   ADD   R8, R0, R8 ;       input2 = input2 + value;
   B   while2 ;   }
endwh2
  
  
   CMP   R7, #"+" ;   if (operator=="+")
   BNE   minus ;   {
   ADD   R5, R4, R8       ;       answer = input1 + input2;
   B   end ;   }
minus
   CMP   R7, #"-" ;   else if (operator=="-")
   BNE   multiply ;   {
   SUB   R5, R4, R8       ;       answer = input1 - input2;
   B   end ;   }
multiply
   CMP   R7, #"*" ;   else if (operator=="*")
   BNE   end ;   {
   MUL   R5, R4, R8       ;       answer = input1 * input2;
end ;   }
  
   MOV   R0, #"=" ;   move ASCII value for "=" to R0
   BL   sendchar ;   print "="
      
   LDR   R6, =0 ;   load value 0 into R6
   LDR   R7, =0 ;   load value 0 into R7
   LDR   R8, =10           ;   load constant value 10 into R8
displaywh  
   CMP   R5, #0 ;   while(answer>0)
   BLS   enddisplaywh ;   {
   MOV   R10, R5          ;       copy value of answer to 'number' to alter in calculations
   LDR   R7, =1 ;       R7 = 1;
whilea  
   CMP   R10, #10       ;       while(number>10)
   BLS   endwha           ;       {
   LDR   R9, =0           ;           quotient = 0;
   MOV R6, R10           ;           remainder = number;
whileb
   CMP   R6, R8           ;           while(remainder>10)   // R6 divided by 10
   BLO   endwhb           ;           {
   ADD   R9, R9, #1      ;               quotient = quotient + 1;          
   SUB   R6, R6, R8     ;               remainder = remainder - 10;          
   B   whileb ;           }
endwhb      
   MOV   R10, R9       ;           store quotient value in 'number'
  
   CMP   R10, #0       ;           if (number>0)       // finding the multiple of 10 that  
   BLS   endifa           ;           {                   // we should divide our answer by
   MUL   R7, R8, R7   ;               R7 = 10^x
endifa ;           }
   B   whilea ;       }
endwha ;      
   LDR   R6, =0          ;       load value 0 into R6 (R6 will store remainder)
whilec
   CMP   R5, R7          ;       while(answer>=10^x)       // dividing our answer by 10^x
   BLO   endwhc          ;       {                                                                                                                          
   ADD   R6, R6, #1     ;           remainder = remainder + 1;          
   SUB   R5, R5, R7   ;           answer = answer - 10^x      
   B   whilec ;       }      
endwhc  
   ADD   R0, R6, #0x30   ;       converting remaining number to ASCII value
   BL   sendchar ;       print ASCII value to console
   B   displaywh ;   }
enddisplaywh      

stop   B   stop

   END