Hello World and Program Structure — C

View, run, and experiment with Hello World and Program Structure — C in CodeUtility's online C IDE.

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🚀 1,076,971 total executions (11,025 this month)

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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.

More than a code runner

Use a multi-file editor, an isolated execution terminal, runtime-specific libraries, persistent workspaces, sharing, and real-time collaboration from the same executor.

How to use this executor?

Choose a runtime, open or create a file, write your code, and select Run. Output appears in the terminal, while signed-in users can keep files in a workspace, install libraries, and collaborate through shares.

Select a version and edit the current file or open another workspace file.
Run the code, provide input in the terminal when requested, and review saved run history.
Use libraries, workspace tools, sharing, and chat when your task needs more than one snippet.

Start coding

VersionSelect a runtime before running. Installed libraries belong to the selected language version.
Open files lists unopened text files. Select one to open it in an available editor tab.
Run executes the active file with its workspace available to the program.
Stop ends the current execution before its time limit.
Advanced Mode opens the IDE layout with a file explorer and movable, resizable terminal.

Workspace and libraries

New file creates a file in the selected parent directory and opens it in the editor.
New folder creates a directory, up to the supported nesting depth.
Upload files adds one or more safe files to a directory.
Download saves a file or a zipped directory to your device.
Copy duplicates a workspace file or directory.
Rename changes a file name and updates its open tab and history.
Move relocates an item; files and directories can also be dragged.
Delete removes an item after confirmation and closes its open editor tab.
Pre-installed Libs shows packages already included in this runtime.
Add Lib installs a private package for your account and selected runtime.

Terminal and assistance

Run history opens previous and next saved outputs.
Run with switches Python between the execution server and Browser Python. Browser Python cannot use workspace files or server-installed libraries.
Copy output copies the current terminal text.
Clear output removes all saved run outputs after confirmation.
Explain summarizes the active code.
Recents opens recent explanations and results.
Settings changes fonts, themes, and visible toolbar buttons.

Sharing and collaboration

Share publishes the current file, a directory, or the whole workspace as a snapshot or live workspace. You control link access and who may save changes.
Logs records saved collaborator actions in a shared workspace.
Share chat lets signed-in participants message, mention people, share code blocks, and see online or typing members.
Live collaboration shows collaborator cursors and saved file updates. View-only users can load the latest version or keep temporary edits.

Quotas and limits

Execution time is limited to 20 seconds per server run. Use Stop when you want to end it sooner.
Workspace storage allows 100 files, 100 directories, and 10 MiB total for each signed-in user workspace and language.
Files and folders are limited to 1 MiB per file and 5 nested directory levels. Files generated by your code follow the same quota.
Private libraries are limited to 10 installed packages for each account and runtime.
Share snapshots can contain up to 100 files, 1 MiB per file, and 2 MiB total.
Share invitations support up to 25 people per share, with access and saving permissions managed separately.
Share chat allows 2,000 characters per message and 10,000 messages per share.
Quota enforcement also applies while code is running. A write that exceeds file count, size, storage, or nesting limits is rejected safely.

Good to know Only run code and install packages you trust. Execution is isolated and limited, but your program can still modify files inside a writable workspace up to its enforced quota.

💡 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);