Online C Compiler - Write, Run & Share C Code Instantly

Our online C compiler provides a powerful and convenient way to write, compile, and run C programs directly in your browser. Whether you're a beginner learning C programming or an experienced developer testing code snippets, our compiler offers a seamless coding experience with real-time output.

Why Use Our Online C Compiler?

• No installation required - Code and run C programs directly from your browser
• Fast compilation - Quick execution with our optimized backend
• Real-time output - See results immediately after execution
• User-friendly interface - Clean, intuitive design with syntax highlighting
• Free to use - No registration or subscription needed
• Mobile-friendly - Code on the go from any device
• Share code easily - Generate shareable links to your code for collaboration or getting help

Getting Started with C Programming

C is a general-purpose, procedural programming language developed in 1972 by Dennis Ritchie at Bell Labs. It's one of the most widely used programming languages of all time and forms the basis for many other languages like C++, Java, and Python. C is particularly known for its efficiency and control, making it ideal for system programming, embedded systems, and applications requiring high performance.

Basic C Program Structure

#include <stdio.h>

            int main() {
                // Your code here
                printf("Hello, World!");
                return 0;
            }

Let's break down each part of this program:

• #include <stdio.h>: This directive includes the standard input/output header file, which provides functions like printf() and scanf().
• int main(): The entry point of the program where execution begins. The int indicates it returns an integer.
• printf("Hello, World!");: Outputs "Hello, World!" to the console.
• return 0;: Indicates successful program completion.

C Programming Basics

Variables and Data Types

C has several basic data types, each with specific sizes and ranges:

• int: Typically 4 bytes, stores integers from -2,147,483,648 to 2,147,483,647
• float: Typically 4 bytes, stores single-precision floating-point numbers
• double: Typically 8 bytes, stores double-precision floating-point numbers
• char: 1 byte, stores single characters

Other types include short, long, and unsigned variants for additional flexibility.

Example of Variables in C

int age = 25;
            float price = 19.99;
            char grade = 'A';

            int a = 1, b = 2, c = 3; // Multiple variables in one line

Control Structures

C provides standard control structures for decision making and loops:

If-Else Statement

if (condition) {
                // code to execute if condition is true
            } else {
                // code to execute if condition is false
            }

For Loop

for (initialization; condition; increment) {
                // code to repeat
            }

While Loop

int i = 0;
            while (i < 5) {
                printf("%d ", i);
                i++;
            }

Switch Statement

int choice = 2;
            switch (choice) {
                case 1:
                    printf("Option 1");
                    break;
                case 2:
                    printf("Option 2");
                    break;
                default:
                    printf("Invalid option");
            }

Functions in C

Functions allow you to organize your code into reusable blocks. They can return values or perform actions without returning anything (void functions).

// Function declaration
            int addNumbers(int a, int b);
            void greet();

            int main() {
                int result = addNumbers(5, 3);
                printf("Sum: %d\n", result);
                greet();
                return 0;
            }

            // Function definition
            int addNumbers(int a, int b) {
                return a + b;
            }

            void greet() {
                printf("Hello!\n");
            }

Declaring functions before use (prototypes) ensures the compiler knows their structure.

Arrays in C

Arrays allow you to store multiple values of the same type, including multi-dimensional arrays.

// One-dimensional array
            int numbers[5] = {1, 2, 3, 4, 5};
            for (int i = 0; i < 5; i++) {
                printf("%d ", numbers[i]);
            }

            // Two-dimensional array
            int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};

Pass arrays to functions like this:

void printArray(int arr[], int size) {
                for (int i = 0; i < size; i++) {
                    printf("%d ", arr[i]);
                }
            }

Pointers in C

Pointers are variables that store memory addresses, offering powerful memory management capabilities.

int var = 20;
            int *ptr = &var;
            printf("Value of var: %d\n", var);
            printf("Address of var: %p\n", &var);
            printf("Value of ptr: %p\n", ptr);
            printf("Value pointed by ptr: %d\n", *ptr);

&var gets the address, and *ptr accesses the value at that address.

File Handling in C

C provides functions for working with files, such as reading and writing.

// Writing to a file
            FILE *file = fopen("example.txt", "w");
            if (file != NULL) {
                fprintf(file, "Hello, File!");
                fclose(file);
            }

            // Reading from a file
            file = fopen("example.txt", "r");
            if (file != NULL) {
                char buffer[100];
                fgets(buffer, 100, file);
                printf("%s", buffer);
                fclose(file);
            }

File modes include "r" (read), "w" (write), and "a" (append).

Frequently Asked Questions

int age;
            printf("Enter your age: ");
            scanf("%d", &age);

char str[20];
            strcpy(str, "Hello");
            printf("%s", str);

Advanced C Programming Concepts

Once you've mastered the basics, you can explore these advanced topics:

• Structures: Group variables of different types

struct Person {
                char name[50];
                int age;
            };
            struct Person p1;
            strcpy(p1.name, "John");
            p1.age = 30;

• Dynamic memory allocation: Using malloc(), calloc(), and free()

int *arr = (int*)malloc(5 * sizeof(int));
            if (arr != NULL) {
                for (int i = 0; i < 5; i++) {
                    arr[i] = i;
                }
                free(arr);
            }

• Function pointers: Pointers that point to functions
• Recursion: Functions that call themselves
• Multi-file programs: Splitting code across multiple source files
• Preprocessor directives: #define, #include, conditional compilation

Common C Programming Mistakes

Be aware of these common pitfalls when learning C:

• Forgetting semicolons at the end of statements
• Not initializing variables before use
• Memory leaks (allocating memory but not freeing it)
• Array index out of bounds errors
• Using the wrong format specifier in printf()/scanf()
• Forgetting to include necessary header files
• Not checking return values of functions that might fail
• Not handling NULL pointers (e.g., after malloc())

Tip: Use debugging tools and always validate inputs/outputs.

C Standard Library Functions

The C standard library provides many useful functions grouped in header files:

• stdio.h: printf(), scanf(), fopen(), etc.
• stdlib.h: malloc(), free(), atoi(), etc.
• string.h: strcpy(), strlen(), strcmp(), etc.
• math.h: sqrt(), pow(), sin(), etc.
• time.h: time(), clock(), etc.

Our online C compiler supports all standard C library functions, so you can experiment freely.

Learning Resources

To continue your C programming journey, check out these resources:

• Books: "The C Programming Language" by Kernighan and Ritchie, "C Primer Plus" by Stephen Prata
• Online courses: Coursera, edX, Udemy offer C programming courses
• Practice problems: LeetCode, HackerRank, CodeChef
• Open source projects: Study and contribute to C projects on GitHub

Our online C compiler is the perfect tool to practice what you learn from these resources. The more you code, the better you'll become!