Ndtyjky

I have this assignment and it has to do all of the following:

I have to: write a MIPS program that reads a string of up to 4 characters from user input. The program must process the user input with a loop. The program must NOT have subprograms. Then, assume that the user input is in base 33. Convert that to a decimal integer. Please help me. I get errors in my code. Also, I don't know how I would convert the string to an integer to later convert into base 10. I thought I was doing it right, but am confused now.

I wrote my code but it seems to not be working.

Here is my code:

.data

Ask:



.asciiz "n Please Enter 4 Charactersn" 



userInput:  .space 20



Answer:



.asciiz "n You Entered : n"



.text 



main:

#addi $t0, 0





li $v0, 4

la $a0, Ask #display question

syscall



li $v0, 8 #get input

la $a0, userInput

li $a1, 20

syscall



li $v0, 4

la $a0, Answer

syscall



li $v0, 4

la $a0, userInput

syscall



lb $s1, 1($a0)  #last digit

lb $s2 2($a0)   #third

lb $s3 3($a0)   #second digit

lb $s4, 4($a0)  #first digit

lb $t0, 0($a0) #checks for n



addi $t1, $zero, 10 #takes in n

addi $t7, $zero, 33   #gets value to multiply

addi $s0, $zero, 1089  #gets 33^2

addi $t5, $zero, 97  #gets 64, smaller than ascii code for 'A'

addi $t6, $zero 96  #gets 96, smaller than ascii code for 'a'

addi $t2, $zero, 65  #loads 47 into $t2, smaller than the ascii code for '0'

#addi $t3, $zero,  55





beq $t0, $t1, Label1



Label1:



blt $s1, $t2, L1

blt $s1, $t5, L2

bgt $s1, $t6, L3



L1: 

    addi $s1, $s1, -48  #subtracts 48 from $s1 which is 48 to get int  from 0 to 9 

L2: 

    addi $s1, $s1, -55 #gets values from 10 to 33

L3: 

    addi $s1, $s1, -87  #gets values from 10 to 33 for small caps



blt $s2, $t2, L4

blt $s2, $t5, L5

bge $s2, $t6, L6



L4: 

    addi $s2, $s2, -48

L5: 

    addi $s2, $s2, -55

L6: 

    addi $s2, $s2, -87



blt $s3, $t2, L7

blt $s3, $t5, L8 

bgt $s3, $t6, L9



L7: addi $s3, $s3, -48

L8: addi $s3, $s3, -55

L9: addi $s3, $s3, -87





blt $s4, $t2, L10

blt $s4, $t5, L11

bgt $s4, $t6, L12



L10: 

    addi $s4, $s4, -48

L11: 

    addi $s4, $s4, -55

L12: 

    addi $s4, $s4 , -87



syscall





add $s5, $zero, 0

add $s5,$s5, $s1

mult $s2, $t7

mflo $s2

add $s5, $s5, $s2

mult $s3, $s0

mflo $s3

add $s5, $s5, $s3

mult $s0, $t7

mflo $s0

mult $s4, $s0

mflo $s4

mfhi $s0

add $s5, $s5, $s4

add $s5, $s5, $s0

syscall



#li $v0, 1

#la $a0, $s5



#la $v0, 4 

#lw $a0, s4



#last system call of the program will be very last instruction

li $v0, 10

syscall  

For starters:

lb $s1, 1($a0)  #last digit

lb $s2 2($a0)   #third

lb $s3 3($a0)   #second digit

lb $s4, 4($a0)  #first digit

lb $t0, 0($a0) #checks for n

You have a 4 character string in a0 - lets assume it was types ABCD

So:

0($a0) will be A

1($a0) will be B

2($a0) will be C

3($a0) will be D

Next assuming s1 is 'A'

Label1:



blt $s1, $t2, L1  # 65

blt $s1, $t5, L2  # 97 

bgt $s1, $t6, L3  # 96





L1: 

    addi $s1, $s1, -48  #subtracts 48 from $s1 which is 48 to get int  from 0 to 9 

L2: 

    addi $s1, $s1, -55 #gets values from 10 to 33

L3: 

    addi $s1, $s1, -87  #gets values from 10 to 33 for small caps

'A' is 65 so will jump to L2, subtract -55 so not 10, then fall into L3 and subtract 87 to make -77.

If it was '9' (57) instead of 'A' it would go to L1, subtract 48, fall to L2, subtract 55, fall to L3, subtract 87.

So for each letter, check, something more like this should occur:

 L1: 

    addi $s1, $s1, -48  #subtracts 48 from $s1 which is 48 to get int  from 0 to 9 



    j  DoneL13

 L2: 



    addi $s1, $s1, -55 #gets values from 10 to 33

    j  DoneL13

 L3: 

    addi $s1, $s1, -87  #gets values from 10 to 33 for small caps



 DoneL13:

Finally you have some sys calls - not sure what they are mean to do do, but am guessing it magically meant to be knowing you want to print the value in s5 ?