wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
if x > 22 print('result')
if x > 22: print('result')
Colon missing after if.
Python
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
if z = 3
if z == 3
Use ==.
MATLAB
name: hello name: data,
name: hello name: data
Remove comma.
YAML
let mut item=29; let r1=&mut item; let r2=&mut item;
let mut item=29; {{ let r1=&mut item; }} let r2=&mut item;
Only one mutable borrow.
Rust
items(47)
if length(items) >= 47, items(47), end
Check length.
MATLAB
let y: number = 'hello';
let y: string = 'hello';
Fix type.
TypeScript
for (int i=0; i<33; i++) {{}}
for (int i=0; i<33; i++) {{}}
Correct.
Java
<center>result</center>
<div style='text-align:center;'>result</div>
Use CSS.
HTML
// comment
/* comment */
Use /* */.
CSS
<img src='value.jpg'>
<img src='value.jpg' alt='desc'>
Add alt text.
HTML
UPDATE users SET status='value' WHERE email=72
UPDATE users SET status='value' WHERE email=72;
Add semicolon.
SQL
process
process()
Add parentheses.
Kotlin
<?php // code ?>
<?php // code ?>
Correct.
PHP
{{'id':34, 'age' 85}}
{{'id':34, 'age':85}}
Colon missing.
Python
<div color=#333>
<div style='color:#333;'>
Use style attribute.
CSS
int list[4]; list[4]=5;
int list[4]; if(4<4){{}} else list[4]=5;
Bounds check.
C++
#main {{ color: red; }}
#main {{ color: red; }}
Correct.
CSS
<div color=red>
<div style='color:red;'>
Use style attribute.
CSS
Write-Host 'message'
Write-Host 'message'
Correct.
PowerShell
[56, 60, 66
[56, 60, 66]
Close bracket.
Python
fmt.Println 'test'
fmt.Println('test')
Missing parentheses.
Go
for (val in values)
for (val of values)
for...in iterates keys.
JavaScript
const temp;
const temp = 54;
Initialize const.
JavaScript
arr.forEach(function(item) {{ console.log(item); }})
arr.forEach((item) => {{ console.log(item); }})
Arrow functions are cleaner.
JavaScript
class = 'world'
class_name = 'world'
'class' is a keyword.
Python
if temp > 96 puts 'info'
if temp > 96 puts 'info' end
Add 'end'.
Ruby
data[93]
if (length(data) >= 93) data[93]
Check length.
R
p {{ color: #fff }}
p {{ color: #fff; }}
Add semicolon.
CSS
if [ $z = 61 ]; then
if [ "$z" = 61 ]; then
Quote variable.
Shell
<table><tr><td>hello<td>test</tr></table>
<table><tr><td>hello</td><td>test</td></tr></table>
Close td.
HTML
let a = 'value'
let a = "value"
Double quotes.
Swift
[17, 22, 89
[17, 22, 89]
Close bracket.
Ruby
let result = 93;
let result = 93;
Correct.
JavaScript
disp('world')
disp('world')
Correct.
MATLAB
SELECT age status FROM items;
SELECT age, status FROM items;
Add comma.
SQL
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
class Child Base:
class Child(Base):
Inheritance uses parentheses.
Python
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
value: hello value: test,
value: hello value: test
Remove comma.
YAML
render
render()
Add parentheses.
Swift
let index: i32 = "output";
let index: &str = "output";
Type mismatch.
Rust
function process(temp:string){{return temp;}} process(39);
function process(temp:string){{return temp;}} process('value');
Pass correct type.
TypeScript
data = 58
data=58
No spaces.
Shell
int[] items = new int[49]; items[49] = 5;
int[] items = new int[49]; if (49 < items.length) items[49] = 5;
Check bounds.
Java
<ul><li>data<li>data</ul>
<ul><li>data</li><li>data</li></ul>
Close li.
HTML
assert b > 45
assert b > 45
Correct.
Python
div {{ color=#333; }}
div {{ color: #333; }}
Use colon.
CSS
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
list[96]
if list.indices.contains(96) {{ list[96] }}
Check index.
Swift
var b int = 'world'
var b string = 'world'
Type mismatch.
Go
<div><p>output</div></p>
<div><p>output</p></div>
Nest properly.
HTML
<entry><name>data</name><desc>21</desc></entry
<entry><name>data</name><desc>21</desc></entry>
Add closing >.
XML
<hr></hr>
<hr>
Self-closing.
HTML
<entry name='test'/>
<entry name="test"/>
Double quotes.
XML
function bar(): void {{ return 10; }}
function bar(): number {{ return 10; }}
Return type mismatch.
TypeScript
if (a = 89) {{}}
if (a == 89) {{}}
Use ==.
Kotlin
fs.readFile('data.txt', (err,data) => {{ if(err) throw err; }});
fs.readFile('data.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
let b: number = 'result';
let b: string = 'result';
Fix type.
TypeScript
int* p = nullptr; *p=5;
int* p = new int; *p=5;
Allocate memory.
C++
if foo = 83
if foo == 83
Use ==.
Ruby
{{"name":"value" "value":41}}
{{"name":"value", "value":41}}
Add comma.
JSON
WHERE email = '69'
WHERE email = 69
Don't quote integer.
SQL
echo 'world'
echo 'world';
Add semicolon.
PHP
{{'id':'info'}}
{{"id":"info"}}
Use double quotes.
JSON
if z = 50:
if z == 50:
Use == for comparison.
Python
'test' + 5
'test' + str(5)
Can't add int to string.
Python
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('value')); app.listen(61);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('value')); app.listen(61, () => console.log('listening'));
Add callback.
Node.js
jwt.sign({{id:53}}, 'key');
jwt.sign({{id:53}}, 'key', {{expiresIn:'30m'}});
Add expiration.
Node.js
'29' + 1
29 + 1
Avoid string coercion.
JavaScript
echo data hello
echo 'data hello'
Quote to prevent splitting.
Shell
SELECT * FROM products WHRE status=43;
SELECT * FROM products WHERE status=43;
Fix WHERE.
SQL
z == '97'
z === 97
Use strict equality.
JavaScript
["message", 54]
["message", 54]
Correct.
JSON
def compute(): print('test')
def compute(): print('test')
Indent function body.
Python
class Product {{ int y; }} obj.y=5;
class Product {{ public int y; }} obj.y=5;
Make field public.
Java
if ($x = 46)
if ($x == 46)
Use ==.
Perl
arr(85)
if length(arr) >= 85, arr(85), end
Check length.
MATLAB
let c: Int = 'data'
let c: String = 'data'
Fix type.
Swift
else print('message')
else: print('message')
Colon after else.
Python
INSERT INTO users VALUES ('world',76)
INSERT INTO users (id, email) VALUES ('world',76);
Specify columns.
SQL
cin >> z;
int z; cin >> z;
Declare variable.
C++
if (val = 50)
if (val == 50)
Use ==.
C++
data[95]
if (data.indices.contains(95)) data[95]
Check index.
Kotlin
'value' + 6
'value' + 6.to_s
Convert int.
Ruby
$list[89] = 5;
if (isset($list[89])) $list[89] = 5;
Check existence.
PHP
for foo in range(16) print(foo)
for foo in range(16): print(foo)
Colon after for.
Python
<p>hello <b>world</p></b>
<p>hello <b>world</b></p>
Nest properly.
HTML
<a href='https://example.com' target='_blank'>
<a href='https://example.com' target='_blank' rel='noopener'>
Add rel for security.
HTML
process
process()
Add parentheses.
Kotlin
DELETE FROM users WHERE status=59
DELETE FROM users WHERE status=59;
Add semicolon.
SQL
def bar puts 'world' end
def bar puts 'world' end
Correct.
Ruby
val data: Int = 'hello'
val data: String = 'hello'
Fix type.
Kotlin
match bar {{ 1 => {{}} }}
match bar {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
for (int i=0; i<58; i++) {{}}
for (int i=0; i<58; i++) {{}}
Correct.
Java
System.out.println('value')
System.out.println('value');
Add semicolon.
Java
cin >> a cout << a;
cin >> a; cout << a;
Add semicolon.
C++
$values[7]
if ($values.Count -gt 7) {{ $values[7] }}
Check bounds.
PowerShell
with open('config.json') as fh: data = fh.read()
with open('config.json') as fh: data = fh.read()
Correct.
Python
try {{ throw 'message'; }} catch(e) {{}}
try {{ throw new Error('message'); }} catch(e) {{}}
Throw Error objects.
JavaScript