Understanding the  Code: Exploring Variables and Functions

In the world of computer programming, understanding  language can be like deciphering a secret code. It's a low-level language that is used to communicate with the hardware of a computer. In this blog post, we'll dive deep into a snippet of  code and unravel its mysteries step by step.

The Main Function

Let's begin by dissecting the main function:

int __fastcall main(int argc, const char **argv, const char **envp)

main proc near

This snippet defines the main function, which serves as the entry point for our program. It takes three parameters: argc (the number of command-line arguments), argv (an array of pointers to the command-line arguments), and envp (an array of pointers to environment variables).

Stack Space Allocation

Next, we encounter the following line:

var_18= dword ptr -18h

This line allocates space for a local variable named var_18 on the stack, reserving 24 bytes (0x18) for it.

Following that, we see:

sub     rsp, 38h

Here, 56 bytes (0x38) are subtracted from the stack pointer (rsp). This allocation of stack space is for local variables and function call purposes.

Initializing Local Variables

The code then initializes var_18 with the value 8:

mov     [rsp+38h+var_18], 8

This line moves the value 8 into the memory location [rsp+38h+var_18], effectively initializing the local variable var_18 with the value 8.

Printing a Welcome Message

The following lines are responsible for printing a welcome message:

lea     rcx, Format     ; "\n\nWelcome to FOR-450 Example #1\n\n\n"

call    printf

Here, the address of a format string is loaded into the rcx register, and then the printf function is called. This will display the "Welcome to FOR-450 Example #1" message on the console.

Variable Manipulation

The code proceeds to load the value stored in the var_18 variable (which is 8) into the edx register:

mov     edx, [rsp+38h+var_18]

This line moves the value of var_18 into edx.

Next, another format string is loaded into rcx, and printf is called again:

lea     rcx, aValueOfXD ; "Value of X = %d\n"

call    printf

This time, the message "Value of X = " followed by the value of X (which is loaded into edx earlier) is printed.

Reading User Input

The line below calls the getchar function to read a character from the standard input (stdin):

call    cs:getchar

This is a simple way to pause the program and wait for user input.

Cleaning Up Stack Space

Before exiting the main function, there is stack space that needs to be cleaned up:

mov     eax, 10h

add     rsp, 38h

The value 0x10 (16 in decimal) is moved into the eax register, and then 56 bytes (0x38) are added back to the stack pointer (rsp), effectively cleaning up the stack space allocated for local variables.


In summary, this program initializes an integer variable X with the value 8, prints a welcome message along with the value of X, waits for user input, and then returns the value 0x10 to indicate successful program execution.

This glimpse into code highlights the intricate dance between memory allocation, variable initialization, function calls, and stack management. While it may seem cryptic at first, understanding these low-level details is crucial for those who want to truly master the art of programming.

Learning More About Assembly Language

If you found the previous explanation of assembly language intriguing and want to delve deeper into this fascinating world, there are plenty of resources available to help you expand your knowledge. Here are some recommended resources to explore:


Online Tutorials and Courses

Assembly Language Communities

Online Assemblers and IDEs

YouTube Tutorials

There are many assembly language programming tutorials available on YouTube. Channels like "TheCherno," "CodePulse," and "Handmade Hero" feature educational content on assembly language and low-level programming.


Practice and Experimentation

One of the best ways to learn assembly language is by hands-on practice. Try writing simple programs, dissect existing assembly code, and experiment with different instructions and optimizations.

Remember that learning assembly language can be challenging, but it's a rewarding journey for those interested in understanding how computers work at the lowest level. With the right resources and dedication, you can master this powerful and essential skill in the world of programming.


Hasan Hashim

Cyber Security and Digital Forensics