ARITHMETIC OPERATIONS

#C CODE SNIPPET
int a = 0;
int b = 1;

a = a + 11;
a = a - b;

a--;
b++;

b = a % 3;

#ASSEMBLY CODE SNIPPET
00401006        mov     [ebp+var_4], 0         ;a = 0  - local variables since they are referenced by the stack
0040100D        mov     [ebp+var_8], 1         ;b = 1
00401014        mov     eax, [ebp+var_4] ❶     
00401017        add     eax, 0Bh               ; a = a + 11
0040101A        mov     [ebp+var_4], eax       ;move result of a + 11 into ebp-4 memory location
0040101D        mov     ecx, [ebp+var_4]       ;move ebp-4 from memory to ecx
00401020        sub     ecx, [ebp+var_8] ❷     ; a = a - b
00401023        mov     [ebp+var_4], ecx       ;move result of a - b into ebp-4 memory location
00401026        mov     edx, [ebp+var_4]
00401029        sub     edx, 1 ❸               ;a--
0040102C        mov     [ebp+var_4], edx
0040102F        mov     eax, [ebp+var_8]
00401032        add     eax, 1 ❹               ;b++
00401035        mov     [ebp+var_8], eax
00401038        mov     eax, [ebp+var_4]
0040103B        cdq
0040103C        mov     ecx, 3
00401041        idiv    ecx
00401043        mov     [ebp+var_8], edx ❺

 * cqd means "convert double to quad"
    - this instruction is used to sign-extend the value in the eax register into the edx register
       - this is typically used when performing division operation to ensure that the full 64-bit result can be stored in both EDX:EAX for a 64-bit dividend
       - the cdq instruction takes the 32-bit value in EAX, extends the sign of that value (MSB) & stores the result in EDX
 * idv means "integer division"
    - this instruction is used to perform signed division
    - unlike the div which is for unsigned division, idiv handles signed numbers by taking the sign into account during the division
    
    - when performing the div or idiv instruction (5), you are dividing EDX:EAX
      by the operand & storing the result in EAX & the remainder in EDX
       - this is why EDX is moved into var_8