Question

Write a program in MIPS assembly language to convert an ASCII number string containing positive and negative integer decimal strings, to an integer. Your program should expect register $a0 to hold the address of a nullterminated string containing some combination of the digits 0 through 9. Your program should compute the integer value equivalent to this string of digits, then place the number in register $v0. If a non-digit character appears anywhere in the string, your program should stop with the value −1 in register $v0. For example, if register $a0 points to a sequence of three bytes 50ten, 52ten, 0ten (the nullterminated string “24”), then when the program stops, register $v0 should contain the value 24ten. Your program should accept input from the keyboard (use the MIPS syscall functionality for I/O). READ THE INSTRUCTIONS IN THE BOOK CAREFULLY. The program is to accept text input from a keyboard (i.e. a string), and translate it to its numeric interpretation. E.g., the string "24" (which has a 2 byte ASCII character representation) should be translated to its decimal value equivalent 24. NO POPUP WINDOWS FOR INPUT - use service code 8 and NOT 54!

Answer 1

Copyable code:

.data

string_ascii: .asciiz   ""

prompt1: .asciiz "Enter an ASCII number string: "

.text

main:

     #prompt the user

     li $v0, 4  

    la $a0, prompt1        

     syscall

     #read the ASCII digit string from the user

     li $v0,8 #take in input

     #$a0 holds the address of a nullterminated string

     la $a0, string_ascii #load the byte space into address

     li $a1, 20 #laod the byte space for string

     syscall

              

     #jump and link to the label convertStringToInt

     jal convertStringToInt

     #store the return value $vo into $a0

     move $a1, $v0

     #print $v0 result

     li   $v0,4

     syscall

              

     #stop program

     li $v0,10

     syscall

#Converts the ASCII decimal string into integer

convertStringToInt:

     # initialize $v0 = 0

     li $v0, 0

     # assign the value '0' to $t6

     li $t6, 0x30

     # assign the value '9' to $t7

     li $t7, 0x39

     #move the the address of a nullterminated string into $t0

     move $t0, $a0

     #load $t1 with the character of the string

     lb $t1, ($t0)

L1:

     #check the character is digit or not

     #if the charcater is less than 0

     #or greater than 9, then goto the label notDigit

     blt $t1, $t6, notDigit

     bgt $t1, $t7, notDigit

     #convert char to integer by substracting $t1 and $t6

     subu $t1, $t1, $t6

     #multiple the value of v0 by 10

     mul $v0, $v0, 10

     # and $v0 and $t1

     add $v0, $v0, $t1

     #increment the $t0 by 1 to get the next character

     addiu $t0, $t0, 1

     #load $t1 with the character of the string

     lb $t1, ($t0)

     #branch to the until end of the string

     bne $t1, $0, L1

     # return integer value

     jr $ra

notDigit:

     #make the value of $v0 as -1

     #if the input string has non-digit character

     li $v0, -1

     # return -1 in $v0

     jr $ra

Sample output 1:

Sample output 2:

Let me know if you have any doubts or if you need anything to change. 

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Thank You!
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