Online C Compiler
Run and debug C code in a simulated CLI—perfect for testing snippets or learning C programming.
Udemy Affiliates: Learn C/C++ to upgrade your skills
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🧩 About This C Online Executor
The CodeUtility C Executor lets you write and run C programs directly in your browser - no installation or compiler setup required. It’s powered by a secure sandbox that supports real C standards, including C89, C99, C11, and the latest version.
This tool uses a real C compiler running in the cloud to compile and execute your code just like a native environment. You can easily test snippets, learn syntax, or practice writing complete programs with input and output.
It’s designed to help learners and developers quickly experiment with C fundamentals - such as data types, pointers, loops, functions, arrays, and structures - without needing to install any compiler or IDE.
⚙️ How to Use This Tool
- 1. Select a C version (C89, C99, C11, or Latest) from the dropdown at the top of the editor.
- 2. Write or paste your C code into the editor area.
- 3. Click Run to compile and execute your program - output will appear in the console below.
- 4. While running, a Stop button appears - click it to stop execution early.
- 5. Use Fix Code to automatically correct minor formatting or syntax issues.
- 6. After fixing, a Fixes button appears - click it to review recent fixes.
- 7. Use the Upload button to import code from a local file, or the Download button to save your current code from the editor.
- 8. Each execution runs up to 20 seconds before automatically terminating.
🧠 Tip: This environment runs real C code securely in your browser - no login or local setup required.
💡 C Basics & Examples You Can Try Above
1. Declaring Variables and Constants
C requires you to declare the type of each variable. Use #define or const to define read-only values.
int age = 30;
double pi = 3.14159;
char grade = 'A';
char name[] = "Alice";
bool isActive = 1; // true
// Constants
#define MAX_USERS 100
const char* COMPANY = "CodeUtility";
2. Conditionals (if / switch)
Use if, else if, and switch for decision making.
int x = 2;
if (x == 1) {
printf("One\n");
} else if (x == 2) {
printf("Two\n");
} else {
printf("Other\n");
}
switch (x) {
case 1:
printf("One\n");
break;
case 2:
printf("Two\n");
break;
default:
printf("Other\n");
}3. Loops
Use for, while, and do-while for repetition.
for (int i = 0; i < 3; i++) {
printf("%d\n", i);
}
int n = 3;
while (n > 0) {
printf("%d\n", n);
n--;
}4. Arrays
Arrays store multiple elements of the same type.
int numbers[3] = {10, 20, 30};
printf("%d\n", numbers[1]);5. Structs
struct lets you group related data.
struct Person {
char name[50];
int age;
};
struct Person p = {"Alice", 30};
printf("%s is %d years old\n", p.name, p.age);6. Console Input/Output
Use printf and scanf for console I/O.
char name[50];
printf("Enter your name: ");
scanf("%s", name);
printf("Hello, %s\n", name);7. Functions
Functions encapsulate reusable logic. Declare return type, name, and parameters.
int add(int a, int b) {
return a + b;
}
printf("%d\n", add(3, 4));8. Pointers
Use pointers to store memory addresses and manipulate data indirectly.
int x = 10;
int* ptr = &x;
printf("Value of x: %d\n", x);
printf("Address of x: %p\n", ptr);
printf("Value from pointer: %d\n", *ptr);
*ptr = 20;
printf("Updated x: %d\n", x);9. File I/O
Use fopen, fprintf, fscanf, and fclose for file operations.
FILE* file = fopen("file.txt", "w");
fprintf(file, "Hello File");
fclose(file);
char line[100];
file = fopen("file.txt", "r");
fgets(line, sizeof(line), file);
printf("%s", line);
fclose(file);10. String Handling
Use functions from <string.h> like strlen, strcpy, and strcmp.
#include <string.h>
char text[] = "Hello";
char copy[10];
strcpy(copy, text);
printf("Length: %lu\n", strlen(copy));
printf("Compare: %d\n", strcmp(copy, "Hello"));11. Dynamic Memory
Use malloc and free for heap allocation.
int* nums = (int*) malloc(3 * sizeof(int));
nums[0] = 1; nums[1] = 2; nums[2] = 3;
for (int i = 0; i < 3; i++) {
printf("%d ", nums[i]);
}
free(nums);