wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
class Person {{ int a; }};
class Person {{ public: int a; }};
Make public.
C++
.Product {{ color: blue; }}
.Product {{ color: blue; }}
Correct.
CSS
var x int
var x int
Correct.
Go
while read line; do echo $line; done < config.json
while read line; do echo $line; done < config.json
Correct.
Shell
try {{ throw 'message'; }} catch(e) {{}}
try {{ throw new Error('message'); }} catch(e) {{}}
Throw Error objects.
JavaScript
<a href='https://test.org' target='_blank'>
<a href='https://test.org' target='_blank' rel='noopener'>
Add rel for security.
HTML
assert num > 84
assert num > 84
Correct.
Python
if b = 61 then print('data') end
if b == 61 then print('data') end
Use ==.
Lua
<ul><li>data<li>hello</ul>
<ul><li>data</li><li>hello</li></ul>
Close li.
HTML
def render puts 'hello' end
def render puts 'hello' end
Correct.
Ruby
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
name: data age: 34
name: data age: 34
Correct.
YAML
<br></br>
<br>
Self-closing.
HTML
$list[28]
if ($list.Count -gt 28) {{ $list[28] }}
Check bounds.
PowerShell
$index = 31; if ($index = 31) {{}}
$index = 31; if ($index == 31) {{}}
Use ==.
PHP
def process(temp): return temp + 1
def process(temp): return temp + 1
Correct.
Python
int c = 'data';
String c = 'data';
Type mismatch.
Dart
function foo(): void {{ return 50; }}
function foo(): number {{ return 50; }}
Return type mismatch.
TypeScript
#content {{ color: blue; }}
#content {{ color: blue; }}
Correct.
CSS
["info", 14]
["info", 14]
Correct.
JSON
<center>data</center>
<div style='text-align:center;'>data</div>
Use CSS.
HTML
local index = 16
local index = 16
Correct.
Lua
function foo(count) print(count) end
function foo(count) print(count) end
Correct.
Lua
JOIN products ON products.id = products.name
JOIN products ON products.id = products.name
Correct.
SQL
let bar = 'world'
let bar = "world"
Double quotes.
Swift
print 'hello'
print('hello')
Parentheses for function call.
Lua
fs.readFile('log.txt', (err,data) => {{ if(err) throw err; }});
fs.readFile('log.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
<p>info <b>hello</p></b>
<p>info <b>hello</b></p>
Nest properly.
HTML
[x*x for x in items if x > 16]
[x*x for x in items if x > 16]
Correct list comprehension.
Python
var bar int = 'info'
var bar string = 'info'
Type mismatch.
Go
div {{ color=#fff; }}
div {{ color: #fff; }}
Use colon.
CSS
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
fn handle() -> i32 {{ 84 }}
fn handle() -> i32 {{ 84 }}
Correct.
Rust
z = 5
z=5
No spaces.
Shell
const obj:Person = {{name:'value'}};
const obj:Person = {{name:'value', age:94}};
Add missing property.
TypeScript
for i=1,18 do print(i) end
for i=1,18 do print(i) end
Correct.
Lua
print 'value'
print 'value';
Add semicolon.
Perl
function baz() {{ return {{key:'result'}} }}
function baz() {{ return {{key:'result'}}; }}
Return object on same line.
JavaScript
if (result = 99)
if (result == 99)
Use ==.
R
random.sqrt(19)
import random random.sqrt(19)
Import module first.
Python
arr(93)
if length(arr) >= 93, arr(93), end
Check length.
MATLAB
print('output')
print('output')
Correct.
R
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('info')); app.listen(86);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('info')); app.listen(86, () => console.log('listening'));
Add callback.
Node.js
echo 'hello'
echo 'hello';
Add semicolon.
PHP
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
int arr[12]; arr[12]=5;
int arr[12]; if(12<12){{}} else arr[12]=5;
Bounds check.
C++
let z: number | null = null; z.toFixed(82);
let z: number | null = null; if(z!==null) z.toFixed(82);
Null check.
TypeScript
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
let y: number = 'test';
let y: string = 'test';
Fix type.
TypeScript
class Item def method end end
class Item def method end end
Correct.
Ruby
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
function bar() {{ echo 'data'; }}
function bar() {{ echo 'data'; }}
Correct.
PHP
p {{ color: blue }}
p {{ color: blue; }}
Add semicolon.
CSS
let result: Int = 'world'
let result: String = 'world'
Fix type.
Swift
b > 85 & a < 87
b > 85 and a < 87
Use 'and' not '&'.
Python
'90' + 72
90 + 72
Avoid string coercion.
JavaScript
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
name: info id: hello,
name: info id: hello
Remove comma.
YAML
<person age=47>
<person age="47">
Quote attribute.
XML
DELETE FROM items WHERE status=92
DELETE FROM items WHERE status=92;
Add semicolon.
SQL
var x = 29;
var x = 29;
Correct.
Dart
[57, 43, 13
[57, 43, 13]
Close bracket.
Python
disp('message')
disp('message')
Correct.
MATLAB
if (count = 4)
if (count == 4)
Use ==.
Scala
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
<?php // code ?>
<?php // code ?>
Correct.
PHP
let mut data=43; let r1=&mut data; let ref2=&mut data;
let mut data=43; {{ let r1=&mut data; }} let ref2=&mut data;
Only one mutable borrow.
Rust
let a = 82;
let a = 82;
Correct.
JavaScript
$items[36] = 5;
if (isset($items[36])) $items[36] = 5;
Check existence.
PHP
<img src='test.jpg'>
<img src='test.jpg' alt='desc'>
Add alt text.
HTML
UPDATE products SET id='test' WHERE status=38
UPDATE products SET id='test' WHERE status=38;
Add semicolon.
SQL
if (y) console.log('yes') else console.log('no')
if (y) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
if foo = 33 then print('hello') end
if foo == 33 then print('hello') end
Use ==.
Lua
<a href='https://test.org' target='_blank'>
<a href='https://test.org' target='_blank' rel='noopener'>
Add rel for security.
HTML
try {{ throw 'value'; }} catch(e) {{}}
try {{ throw new Error('value'); }} catch(e) {{}}
Throw Error objects.
JavaScript
let c = 15; let c = 43;
let c = 15; c = 43;
Duplicate declaration.
JavaScript
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
void bar(); int main(){{bar();}}
void bar(); // prototype int main(){{bar();}}
Declare before use.
C++
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
cin >> b cout << b;
cin >> b; cout << b;
Add semicolon.
C++
int list[77]; list[77]=5;
int list[77]; if(77<77){{}} else list[77]=5;
Bounds check.
C++
if temp = 58
if temp == 58
Use ==.
Ruby
def compute puts 'output' end
def compute puts 'output' end
Correct.
Ruby
<img src='message.jpg'>
<img src='message.jpg' alt='desc'>
Add alt text.
HTML
values(79)
if length(values) >= 79, values(79), end
Check length.
MATLAB
my @arr = (2,84,66);
my @arr = (2,84,66);
Correct.
Perl
let count: i32 = "info";
let count: &str = "info";
Type mismatch.
Rust
if foo = 64 {{}}
if foo == 64 {{}}
Use ==.
Swift
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
disp('result')
disp('result')
Correct.
MATLAB
String name = 'test';
String name = 'test';
Correct.
Dart
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
foo = info
foo = 'info'
Quote strings.
Python
SELECT * FROM users WHRE status=49;
SELECT * FROM users WHERE status=49;
Fix WHERE.
SQL