DEV Community: Abdulsalam Yusuf

Memory layout in C

Abdulsalam Yusuf — Mon, 22 Jul 2024 16:48:48 +0000

Introduction

Memory layout refers to how a computer’s memory is organized and structured. It defines how memory is divided and utilized by various system components.

This is crucial in C as it directly impacts how variables, functions, and data structures are stored and accessed during execution.

In this article, we’ll learn about the fundamental aspects of the memory layout in the C.

Segments In C’s Memory Layout

The memory layout in C consists of different segments, below are the segments;

Text(Code) segment.
Data segment.
Heap.
Stack.

The diagram below depicts C’s memory layout.

Now let’s discuss the segments in detail.

Text(code) Segment

The text segment is a region of memory in a C program that stores the compiled machine code instructions. These instructions constitute the executable logic of the program and are responsible for defining its behavior.

Here's a simple example to illustrate the concept of the text segment in a C program:

#include <stdio.h>

int main() {
    int x = 5;
    int y = 10;
    int sum;

    sum = x + y;
    printf("The sum of %d and %d is %d\n", x, y, sum);

    return 0;
}

The compiler converts the source code into machine code when this program is compiled. This machine code constitutes the logic and behavior of a program and is stored in the text segment.

While we can't directly see the machine code. We can understand that the text segment contains the compiled instructions.

Essentially, the text segment holds instructions that define how the program behaves when it's executed.

Data segment

The data segment is divided into two parts:

Initialized data segment
uninitialized data segment

Initialized Data Segment

The initialized data segment consists of global, extern, static(both local and global), and constant global variables initialized beforehand. The initialized data segment has two sections, the read-only and read-write sections.

Variables with predefined values that can be modified i.e. initialized global, extern, and static(both local and global) variables are stored in the read-write section. Constant variables on the other hand come under the read-only section.

Here's an example illustrating variables stored in the initialized data segment, both in the read-write and read-only sections:

#include <stdio.h>

// Global variable (read-write section)
int globalVar = 10;

// External variable declaration (read-write section)
extern int externVar;

// Static global variable (read-write section)
static int staticGlobalVar = 20;

// Constant global variable (read-only section)
const int constGlobalVar = 30;

int main() {
    globalVar += 5;
    staticGlobalVar += 10;

    printf("Global variable: %d\n", globalVar);
    printf("Extern variable: %d\n", externVar);  // Assuming externVar is defined in another file
    printf("Static global variable: %d\n", staticGlobalVar);
    printf("Constant global variable: %d\n", constGlobalVar);

    return 0;
}

This illustrates variables stored in the read-write and read-only sections of the initialized data segment.

Uninitialized Data Segment

The uninitialized data segment also known as BSS(Block started by symbol) segment consists of uninitialized global, extern, and static(both local and global) variables.

These variables are initialized to zero by default before the program's execution. They have read-write permissions. Thus allowing them to be both read from and written to during the program's execution.

Example:

#include <stdio.h>

// Uninitialized global variable (goes to the BSS segment)
int globalVar;

// Uninitialized static global variable (also goes to the BSS segment)
static int staticGlobalVar;

int main() {
    // Uninitialized local static variable (goes to the BSS segment)
    static int staticLocalVar;

    printf("Uninitialized Global Variable: %d\n", globalVar);
    printf("Uninitialized Static Global Variable: %d\n", staticGlobalVar);
    printf("Uninitialized Static Local Variable: %d\n", staticLocalVar);
    return 0;
}

In this program, the uninitialized variables will contain zero or null values by default. This is due to automatic initialization by the compiler. This shows the behavior of variables stored in the BSS segment.

Heap

The heap is a region of memory used for dynamic memory allocation during runtime. This allows memory to be allocated and released as needed during program execution. Functions such as malloc(), calloc(), realloc(), and free() are used for memory allocation and deallocation in the heap. The heap is accessible to all parts of the program.

Example:

#include <stdio.h>
#include <stdlib.h>

int main() {
    // Dynamically allocate memory for an integer variable on the heap
    int *ptr = (int *)malloc(sizeof(int));

    return 0;
    }

This code snippet demonstrates a simple use of dynamic memory allocation in C. It draws attention to the steps involved in requesting memory, initializing a pointer to that memory, and managing memory properly to avoid leaks. While error handling and memory deallocation are not included in this example, these are crucial components of working with dynamic memory in practical applications.

Stack

The stack segments primary function is to manage function calls and store local variables. This part is crucial in a program's memory layout, as it controls the flow within a program. The stack adopts a Last In, First Out (LIFO) structure, meaning the most recently added data is removed first. This makes the stack very efficient for managing local variables and nested function calls.

Example:

#include <stdio.h>

void functionA(int n) {
    int a = n + 1; // Local variable
    printf("In functionA, a = %d\n", a);
}

void functionB() {
    int b = 10; // Local variable
    printf("In functionB, b = %d\n", b);
    functionA(b); // Call to functionA
}

int main() {
    int x = 20; // Local variable
    printf("In main, x = %d\n", x);
    functionB(); // Call to functionB
    return 0;
}

The code explains how stack frames store local variables. New stack frames are created by the function calls and are eliminated when the functions return. The printf instructions facilitate the visualization of each function's local variable values. The execution flow follows the calls to and returns from functions.

Conclusion

C programmers can improve their coding techniques and gain a better understanding of how their programs interact with memory by mastering these concepts. Understanding memory layout is a vital skill in your programming toolbox, whether you're optimizing for performance or troubleshooting a complex problem.

Feel free to follow, comment, and leave claps. Happy Coding!

Let’s connect on LinkedIn.

“Is 2024 a Leap Year?”, Here’s how to check, using C language.

Abdulsalam Yusuf — Wed, 17 Jan 2024 09:49:15 +0000

Introduction

What is a leap year?:

A leap year is a year that is a day longer than other years, i.e. it has 366 days instead of 365 days.

When is the extra day?:

In a leap year, the extra day is the 29th of February, instead of the normal 28 days. This extra day brings the total number of days to 366 days.

Why do leap years exist?:

Leap years exist to adjust our calendar system. To keep it synchronized with the Earth's orbit around the Sun.

In this article, you’ll write a program in C to check if a year is a leap year, or not.

Prerequisite

Understanding of the basics of C programming and its syntax.
An integrated development environment is set up on your machine.
Basic knowledge of your integrated development environment.

Terminologies to understand to aid with this lesson

The rules for leap years are:

If a year is divisible by 4 without remainder, it is a leap year.
For centurial years, if it is divisible without remainder by 100 but not 400, it is not a leap year.

Steps

Let’s begin, you’ll create a program in C language to check if a year is a leap year.

Step 1 - Set up your IDE(Integrated Development Environment)

Create a file in your IDE that’ll store your source code. This is a fundamental step in establishing a well-organized and efficient development environment.

Step 2 - Header File

Include the standard input/output library.

#include <stdio.h>

#include <stdio.h> includes the standard input/output library. Which is necessary to use functions like printf and scanf.

Step 3 -Declare Variable

Declare a variable.

int year;

An integer variable named year is declared. This variable will store the user-inputted year.

Step 4 - User-Input

Code to accept user input is required.

printf("Enter year: ");
scanf("%d", &year);

printf("Enter year: "); prompts the user to enter a year. While scanf("%d", &year); reads the inputted year and stores it in the variable year.

Step 5 - Leap Year Check

Next, you’ll write your code to check if the year inputted is a leap year or not.

Step 5.1 - If Statement**

if (year % 400 == 0)
{
    printf("%d is a leap year", year);
}

The if statement checks if the inputted year is divisible by 400 without remainder. If it is, a message indicating it is a leap year will be printed.

Step 5.2 - else if statement**

else if (year % 4 == 0)
{
    printf("%d is a leap year", year);
}

If the condition is not met in the first if statement, the program moves to the else if statement. if the inputted year is divisible by 4, it’ll print a message indicating it is a leap year.

Step 5.3 - else statement**

else
{
    printf("%d is not a leap year", year);
}

If both conditions in the if and else if statements are not satisfied, the program executes the else statement. This means the year inputted is not divisible by 400 and 4 without remainder. A message indicating the year is not a leap year will be printed in this case.

return 0;
}

This indicates the successful execution of the program.

Step 6 - Execute Code

Now, you’ll check if 2024 is a leap year or not.

In your IDE, run your code and input 2024 as the user input when prompted to “Enter year:”.

As 2024 can be divided by 4 without remainder, your terminal would return the output below:

Let’s see what happens when we enter 2023 when prompted to “Enter year”.

As 2023 cannot be divided by 400 or 4 without remainder, the output below will be printed on your terminal:

Conclusion

Congratulations!, you’ve successfully run a program to check if 2024 is a leap year. By utilizing some basic syntax in C, you’ve gained experience with how functions like printf, scanf, if, else if, and else statements work.

If you enjoyed this article, please follow, like, and leave a comment. Let’s connect on LinkedIn.

Happy Coding!

How to write a simple C program to check if a number is prime using Visual Studio code.

Abdulsalam Yusuf — Fri, 29 Dec 2023 16:05:03 +0000

Introduction

C is a procedural language. it is renowned for its portability, efficiency, and simple syntax.

Visual Studio Code is a development tool. Inbuilt with a code editor that supports development processes and more.

In this article, you’ll learn to write a simple C program to check if a number is prime using Visual Studio Code.

Prerequisite

Basic knowledge of C programming and its syntax.
Visual Studio Code is installed on your machine. Go to the official website to install it.

Terminologies to understand to aid with this lesson

Prime number - This is a number that can only be divided by one and itself, for example, 2, 3, 5, 7… etc.
Composite number - is a positive integer divided by 1 and other numbers apart from itself, for example, 4, 6, 8, 9… etc.

Steps

Let’s dive in by breaking down the processes involved in this article.

Step 1 - Download Extensions

Extensions are software that extends and enhances the functionality of the editor.

Launch Visual Studio Code and click on Extensions. It can also be accessed using the shortcut keys ctrl+shift+X or the command key for MAC. Install the following extensions:

C/C++ Extension Pack:

The C/C++ Extension Pack provides a comprehensive development environment for C and C++ programming in Visual Studio Code. This extension pack includes essential tools, language support, debugging capabilities, and extra features tailored for C and C++ development.

C/C++ Extension:

The C/C++ extension is a core component within the extension pack. It focuses on providing language support for C and C++ in Visual Studio Code. This includes features such as syntax highlighting, code suggestions, debugging support, etc.

Code Runner:

The Code Runner extension is a tool that allows the execution of code snippets or entire files

Step 1.1 - Change Settings

Click the gear icon on the bottom-left corner of your screen and click on Settings. Or, use the shortcut keys ctrl+,, the command key for Mac.

Next, enable the Code-runner: Run In Terminal feature.

Input “run code in terminal” in the search bar and check the Code-runner: Run In Terminal checkbox.

The Code-runner: Run In Terminal feature allows user input in the terminal. In this lesson, user input handling is required. i.e. if your code prompts for user input, you can provide it within the terminal.

Step 2 - Open a folder

A folder has many uses such as file organization, namespace management, etc.

Navigate the Explorer tab or use the shortcut keys ctrl+shift+E, the command key on Mac.

Click Open Folder and proceed to create a new folder on your file explorer/manager.

Name the folder whatever you want or you can name it “C”. Click Select Folder after.

Step 2.1 - Create a file

A file serves many functions, in this lesson, you’ll be storing your source code in a file.

Click on your folder, and beside it, three icons will appear, click the New File icon.

Name your file with the .c extension to specify the C source code. Click enter to save the file.

Step 3 - Code

Your workspace is set up, Next, you’ll write your code to check if a number is prime. In your editor, follow the steps below:

Step 3.1 - Header file

Include the standard input/output and math libraries.

#include <stdio.h>
#include <math.h>

#include <stdio.h> includes the standard input/output library. This library is used for input/output operations.

#include <math.h> includes the math library. This library is used for mathematical functions.

Step 3.2 - Entry point

Include the int main() function.

#include <stdio.h>
#include <math.h>

int main()
{

}

The int main function is the entry point, it returns an integer value(often 0) to state success. An entry point is where program execution starts.

Step 3.3 - Declare variables and user input

Declare Variables:

#include <stdio.h>
#include <math.h>

int main()
{
    int number;
    int i, value1, value2, count = 0;
}

int number stores the user input. While int i, value1, value2, count = 0; declare variables for loop control, intermediate values, and a counter.

Next, add code to accept user input:

#include <stdio.h>
#include <math.h>

int main()
{
    int number;
    int i, value1, value2, count = 0;
    printf("Enter a number: ");
    scanf("%d", &number);
}

printf("Enter a number: ") prompts the user to enter a number. scanf("%d", &number); reads the user input and stores it.

Step 3.4 - Find the square root

#include <stdio.h>
#include <math.h>

int main()
{
    int number;
    int i, value1, value2, count = 0;
    printf("Enter a number: ");
    scanf("%d", &number);

    value1 = ceil(sqrt(number));
    value2 = number;
}

value1 = ceil(sqrt(number)); calculates the square root of number using the sqrt function. The ceil function approximates the square root to the nearest integer.

value2 = number is initialized to the value of number. This will be used in later calculations or conditions. i.e. the prime number checking logic.

Step 3.5 - Loop iteration

#include <stdio.h>
#include <math.h>

int main()
{
    int number;
    int i, value1, value2, count = 0;
    printf("Enter a number: ");
    scanf("%d", &number);

    value1 = ceil(sqrt(number));
    value2 = number;

    for(i = 2; i <= value1; i++)
    {
        if(value2 % i == 0)
            count = 1;
    }
}

The loop checks the divisibility of value2 by i. If true, count is set to 1, else it remains 0.

Step 3.6 - Check if the number is prime

#include <stdio.h>
#include <math.h>

int main()
{
    int number;
    int i, value1, value2, count = 0;
    printf("Enter a number: ");
    scanf("%d", &number);

    value1 = ceil(sqrt(number));
    value2 = number;

    for(i = 2; i <= value1; i++)
    {
        if(value2 % i == 0)
            count = 1;
    }
    if((count == 0 && value2 != 1) || value2 == 2 || value2 == 3)
    {
        printf("%d is a prime number", value2);
    }
    else
    { 
        printf("%d is not prime number", value2);
    }
    return 0;
}

The if statement checks if the number is prime. If the conditions are true, it prints the number is a prime number, if false, it prints it is not a prime number. return 0 indicates the program has been executed successfully.

Step 4 - Run Code

To run your code, click on the Run Code icon on the top-left corner of your screen(first icon). Or use the shortcut keys ctrl+alt+N, the command key on Mac.

Step 5 - Terminal Input

After clicking the Run Code icon, the terminal will appear at the bottom of your screen. You will see a prompt that says “Enter a number” on the terminal. Please input a number in the terminal when prompted.

If the number is prime, the output below is displayed;

Otherwise, this output below is displayed;

Conclusion

In this tutorial article, you wrote a C program to check if a number is prime. Also leveraging the capabilities of Visual Studio code as a powerful integrated development environment(IDE). You covered inputs, loops, and math functions. All basics for a solid foundation in C programming.

If you enjoyed this tutorial and would like to learn more on this blog, feel free to follow, comment, and leave claps. Happy Coding!

Let’s connect on LinkedIn.