I have a school assignment that has got me stumped. The program is to read in values, pass them into an array, sum the values, and average them.
.DATA
inputArray DWORD 100 DUP(?)
elementCnt DWORD 0
number DWORD ?
prompt BYTE "Enter values. (-1 to quit) ", 0
string BYTE 40 DUP (?)
resultLbl BYTE "The sum is", 0
sum BYTE 11 DUP (?), 0
.CODE
_MainProc PROC
mov eax, 0 ; EAX = 0
lea ebx, inputArray ; EBX = [inputArray]
mov ecx, elementCnt ; ECX = 0
getInputs:
input prompt, string, 40 ; Get input from the user
atod string ; Convert to decimal, result stored in EAX
mov [ebx + (ecx * 4)], eax ; Move the user input into the array
add ecx, 1
cmp eax, -1
jg getInputs
mov eax, 0
mov eax, 0
lea ebx, inputArray
mov ecx, elementCnt
push ebx
push eax
call sumAndAverage
quit:
mov eax, 0
ret
_MainProc ENDP
sumAndAverage PROC
push ebp
mov ebp, esp
push eax
sumValues:
add eax, [ebx + ecx] ; <------ CRASHING HERE
loop sumValues
xor edx, edx
idiv ecx
pop eax
pop ebp
ret
sumAndAverage ENDP
END
I am not the greatest at assembly. It is definitely not my language.
input and prompt are both macros defined in a header named io.h. The section of code that uses them works fine. To be honest, I have an inkling of an idea what might be causing the crash, but I am not sure. The code is crashing because it is trying to access a memory location it’s not allowed to access. This means that something is wrong with my code to read the values from the array.
If someone could explain to me what my problem is without providing a solution, I’d appreciate it.
>Solution :
Taking a look at this section of code:
sumValues:
add eax, [ebx + ecx] ; <------ CRASHING HERE
loop sumValues
loop decrements ecx. Since ecx is zero when you enter sumAndAverage (you should be able to figure out why this is), ecx becomes negative as you iterate through the loop. This causes the effective address of [ebx + ecx] to go out of bounds. This qualifies as a segmentation fault.