C / C++ Online Compiler

Write C or C++, press Run — compiled and executed in your browser, with cin/scanf input.

Free
No signup
Nothing uploaded
No watermark

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Source

21 lines

// C++ compiles and runs here, in your browser.
#include <iostream>
#include <vector>
using namespace std;

int main() {
    string name;
    int n;
    cout << "What is your name? ";
    cin >> name;
    cout << "How many squares? ";
    cin >> n;
    vector<int> squares;
    long long sum = 0;
    for (int i = 1; i <= n; i++) { squares.push_back(i * i); sum += i * i; }
    cout << "Hello, " << name << "! The first " << n << " squares:";
    for (int s : squares) cout << " " << s;
    cout << "\nTheir sum is " << sum << endl;
    return 0;
}

Program output

549 B

Ctrl+Enter · C / C++ · runs in your browser

Press Run to execute the program. Output appears here.

Read in this tab. Nothing you paste or open is ever uploaded.

How to Use the C / C++ Online Compiler Online

Compiles and runs C and C++ in your browser: a real compiler and linker are loaded into the tab, your source becomes a real program, and its output — or the compiler's own error messages, with line numbers — appears beside the code. Input works as it does at a terminal: when the program reads from cin or scanf, the prompt appears in the output pane and you type the answer. This is the online compiler shape that students, interview candidates and anyone checking a snippet need, without an account, a queue or a server compiling on your behalf: nothing you write leaves the browser. The compiler is large and takes a while to load the first time in a visit; it is then cached, so later runs are quick. There is no operating system underneath — no files, network or threads — but the standard library is complete: containers, strings, algorithms, math and formatted I/O all work, and a runaway program is stopped after ten seconds.

No software to install Free Works on any device

Step-by-Step Guide to Using the C / C++ Online Compiler

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1. Write or paste your program on the left — a working example is loaded to start from
2

2. Press Run (or Ctrl+Enter)

When the program asks for input, the question appears in the output with a box — type the answer and press Enter, and it carries on.
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3. Output appears beside the code

errors name the line. Fix, run again, and Download the file when it is right.

Try it now

What is the C / C++ Online Compiler?

C files

.C .H .CPP

Write C or C++, press Run — compiled and executed in your browser, with cin/scanf input.

Why Use an Online File Viewer?

Not every computer has the right program for a YAML, VCF, SRT or log file, and installing one just to look inside is a chore. A viewer opens the file in your browser and shows it neatly next to its source text.

“Sometimes you just need to see what is inside the file.”

No software to install
Data laid out as tables
Subtitles shown with timings
Code tried out in the page

Colour-coded source text
Contacts and calendars readable
Works on shared computers
Private files stay local

Popular Uses for Code and Data Viewers

People open these when a file arrives and nothing on the computer will show it.

Checking a JSON response Open a JSON or YAML file as a readable tree instead of one long line.
Reading contact backups See the names and numbers inside a VCF file exported from a phone.
Opening calendar invites Read the date, time and place in an ICS file before adding it.
Checking subtitles View SRT or VTT subtitles with their timings to spot a missing line.
Reading log files Scroll through a server or app log with the lines laid out clearly.
Previewing CSV and TSV Look at a data file as a table without opening a spreadsheet program.
Trying a code snippet Run a short Python or JavaScript example from a tutorial and see the output.
Viewing SVG graphics See how an SVG icon or drawing looks next to the markup behind it.

What You Can Do with the C / C++ Online Compiler

Accepts C, H, CPP, HPP, CC

Highlighting follows the language’s real grammar rather than a list of keywords

Reads a file you have not yet decided to trust, without registering a handler for it

Why Use ToolXkit for C / C++ Online Compiler?

Your files stay with you

Everything runs inside your browser. Nothing you open or type is uploaded to a server.

File Viewers for Different Users

Developers

Inspect config, env and data files on any machine without an editor installed.

Programming students

Try small programs in Python, JavaScript or SQL without setting anything up.

IT support staff

Open logs, HAR files and settings files that users send in.

Office workers

Read contact, calendar and CSV files that arrive as email attachments.

Video editors

Check subtitle files for timing and text before a video goes out.

Data analysts

Glance at CSV, TSV, JSONL and GeoJSON files before loading them anywhere.

Best Times to View a File Online

A browser viewer is handy when you are:

Using a borrowed or office computer
Opening an unfamiliar attachment
Checking a file before importing it
Learning to code without installing
Debugging a settings file
Proofreading subtitle timings
Looking inside a phone backup
Reviewing a server log

Frequently Asked Questions

Answers to common questions about this tool.

Is this a real compiler?

Yes — a genuine C/C++ compiler and linker, loaded into your browser, producing a real program that then runs in the tab. Compile errors are the compiler's own, with the line they refer to. The compiler is large, so the first run of a visit waits while it loads; after that it is cached and runs start in a second or two.

C or C++ — how does it know?

From the source: iostream, std::, classes, templates or cout mark C++; stdio.h and friends with none of those mark plain C. Both use the same standard library set, so printf works in C++ and a C file compiles as C.

How does input work?

When the program reads from cin, scanf or getline and nothing is waiting, its prompt appears in the output pane with a box. Type the line, press Enter, and the program carries on; Run starts over.

What is not available?

Files, the network, threads and system() — there is no operating system underneath, only a small in-memory filesystem. Standard containers, strings, algorithms, math and formatted I/O all work. A program that runs longer than ten seconds is stopped.

Does C / C++ Online Compiler upload my file?

No. The file is read by your browser and shown on screen without being sent anywhere. Config files with passwords, contact lists and logs remain on your own computer.

Do the online compilers run real code?

Some languages, such as Python, JavaScript, TypeScript, Lua and SQL, run inside your browser. For others, the page is mainly for reading and sharing the code, so read the note on that page to know what to expect.

Does C / C++ Online Compiler cost anything or need a login?

Neither. There is no fee, no sign-up and no cap on how many files you open. It works the same on a work laptop, a home computer or a phone.

What if my file is very large?

Large logs and data files depend on your device’s memory, because the whole file is read in the browser. If a huge file feels slow, try a computer with more memory or view a smaller part of it.

Can I open a file from my phone?

Yes. Use the file picker to choose it from your phone’s storage or a downloaded attachment, and the contents appear on the page. A larger screen is easier for long files, but everything works on mobile.

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