Project Configuration

Visual Studio doesn't provide native assembly language support, but you can leverage the Microsoft Macro Assembler (MASM) to write and debug assembly code within your projects.

Creating a New Empty Project

1. Launch Visual Studio and create a new empty C++ project
2. Right-click on the project name in Solution Explorer
3. Navigate to Build Dependencies → Build Customizations
4. Check the masm option (.targets, .props)
5. Click OK to confirm

Adding Source Files

1. Right-click on the Source Files folder in Solution Explorer
2. Select Add → New Item
3. Choose C++ File and name it with an .asm extension (for example, calculator.asm)
4. Click Add to create the file

Writing Assembyl Code

The following example demonstrates a simple subtraction operation:

.486
.MODEL FLAT, STDCALL
ExitProcess PROTO, dwExitCode:DWORD

.DATA
    RESULT DB ?

.CODE
    MAIN PROC
        MOV BL, 5AH
        SUB BL, 1EH
        MOV RESULT, BL
        INVOKE ExitProcess, 0
    MAIN ENDP

END MAIN

This program subtracts the value 1EH from 5AH and stores the result in the RESULT variable.

Debugging the Code

Setting Breakpoints

Click on the left margin next to the .DATA line to set a breakpoint. A red dot will appear indicating the breakpoint is active.

Starting the Debugger

Click the Local Windows Debugger button in the toolbar to begin debugging.

Examining Register Values

1. Open the Watch window (Debug → Windows → Watch)
2. Enter the register names you want to monitor, such as BL and RESULT
3. Press F11 to step through each instruction line by line
4. Observe how the register values change as each instruction executes

Alternative Approach: Inline Assembly

You can also write assembly code directly in C++ files using the __asm keyword:

#include <iostream>

extern "C" int Calculate();

int main() {
    std::cout << "Calling assembly function..." << std::endl;
    int result = Calculate();
    std::cout << "Result: " << result << std::endl;
    return 0;
}

Create a separate .asm file with the implementation:

.code
Calculate PROC
    mov eax, 100
    sub eax, 37
    ret
Calculate ENDP

Configure the project properties to include the .asm file in the Linker → Input → Additional Dependencies section.