Using the previous in-class assignment as reference, create a procedure that calculates the average grade using an array of grades and returns the letter grade in eax. The function should take 2 parameters, the address to an array and the size of that array. Rules: Main should only be used to set the parameters and call your procedure You cannot use memory operands (by name) inside of the procedure, they must be passed as parameters.

In assembly language using MASM Visual Studio

This is my code so far. Please help me fix it.

My Code:

.386 .MODEL FLAT, stdcall .STACK 4096 ExitProcess PROTO, dwExitCode:DWORD

.data array WORD 100,90,60,80,70,100 lenA EQU [$-array]/2 letterGrade DB 0

.code _main PROC

; Calculate the average of the grades use a loop mov edx, lenA push edx, size of array lea esi, [array] push esi; address of array call GetLetterGrade add esp, 8 mov letterGrade, al

GetLetterGrade PROC push ebp mov ebp, esp mov ecx, [ebp + 12] dec ecx mov edx, 0 mov esi, [ebp + 8]

L1: mov ax, WORDPTR [esi + ecx * 2] add dx, ax dec ecx cmp ecx, 0 jge L1

movzx eax, dx cdq mov ebx, [ebp + 12] div ebx

; Determine if the average is an A, B, C, D or F ; Use a series of cmp + jump instructions to build your if else statements

COMMENT ! IN C++ this if-else statements would look like

if (avg >= 90) letterGrade = 'A'; else if (avg >= 80) letterGrade = 'B'; else if (avg >= 70) letterGrade = 'C'; else if (avg >= 60) letterGrade = 'D'; else letterGrade = 'F'; !

; avg is in eax cond1: cmp eax, 90 ; if (avg >= 90) letterGrade = 'A'; JL cond2 mov eax, 'A' jmp next

cond2: cmp eax, 80 jl cond3 mov eax, 'B' jmp next

cond3: cmp eax, 70 JL cond4 mov eax, 'C' jmp next

cond4: cmp eax, 60 JL cond5 mov eax, 'D' jmp next

cond5: mov eax, 'F'

next: pop ebp ret

GetLetterGrade ENDP

INVOKE ExitProcess, 0 _main ENDP END

Sol20:

There are a few issues with the provided code. Here are some changes that should fix the issues:

• In the GetLetterGrade procedure, the division should be done by the size of each element (in this case, 2 bytes), not the size of the array. So, instead of mov ebx, [ebp + 12], use mov ebx, 2.
• Instead of using mov letterGrade, al, use movzx eax, al to zero-extend the result of the procedure to a 32-bit register.
• In the GetLetterGrade procedure, change the order of the push instructions so that the address of the array is pushed last. This is because the first argument is pushed last in the CDECL calling convention.
• In the GetLetterGrade procedure, add the prologue and epilogue macros to set up and clean up the stack frame.

Here is the modified code:

.386

.MODEL FLAT, C

.STACK 4096

ExitProcess PROTO, dwExitCode:DWORD

.DATA

array WORD 100, 90, 60, 80, 70, 100

lenA EQU ($ - array) / 2

letterGrade DB 0

.CODE

GetLetterGrade PROC, pArray:PTR WORD, arraySize:DWORD

prologue

push ebx

push esi

push edi

mov ecx, arraySize

dec ecx

mov edx, 0

mov esi, pArray

L1:

mov ax, [esi + ecx * 2]

add dx, ax

dec ecx

cmp ecx, 0

jge L1

mov ebx, 2 ; size of each element

cdq

idiv ebx ; divide the sum by the number of elements

cmp eax, 90 ; determine letter grade based on the average

jl cond2

mov eax, 'A'

jmp next

cond2:

cmp eax, 80

jl cond3

mov eax, 'B'

jmp next

cond3:

cmp eax, 70

jl cond4

mov eax, 'C'

jmp next

cond4:

cmp eax, 60

jl cond5

mov eax, 'D'

jmp next

cond5:

mov eax, 'F'

next:

pop edi

pop esi

pop ebx

ret

GetLetterGrade ENDP

main PROC

push lenA

lea esi, array

push esi ; address of array

call GetLetterGrade

add esp, 8

movzx eax, al ; zero-extend to 32 bits

mov letterGrade, al

INVOKE ExitProcess, 0

main ENDP

END