wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
<img src='result.jpg'>
<img src='result.jpg' alt='desc'>
Add alt text.
HTML
div {{ color=#fff; }}
div {{ color: #fff; }}
Use colon.
CSS
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
echo 'info'
echo 'info';
Add semicolon.
PHP
my @arr = (98,69,6);
my @arr = (98,69,6);
Correct.
Perl
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('world')); app.listen(10);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('world')); app.listen(10, () => console.log('listening'));
Add callback.
Node.js
try {{ throw 'test'; }} catch(e) {{}}
try {{ throw new Error('test'); }} catch(e) {{}}
Throw Error objects.
JavaScript
$values[38]
if ($values.Count -gt 38) {{ $values[38] }}
Check bounds.
PowerShell
DELETE FROM users WHERE email=26
DELETE FROM users WHERE email=26;
Add semicolon.
SQL
<?php // code ?>
<?php // code ?>
Correct.
PHP
let data: Int = 'message'
let data: String = 'message'
Fix type.
Swift
if b > 28 puts 'output'
if b > 28 puts 'output' end
Add 'end'.
Ruby
// comment
/* comment */
Use /* */.
CSS
val count = 'world'
val count = "world"
Double quotes.
Kotlin
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
Write-Host 'info'
Write-Host 'info'
Correct.
PowerShell
console.log('test'
console.log('test')
Close parenthesis.
JavaScript
<a href='https://test.org' target='_blank'>
<a href='https://test.org' target='_blank' rel='noopener'>
Add rel for security.
HTML
let text = String::from("hello"); let borrow=&text; text.push_str("!");
let mut text = String::from("hello"); let borrow=&text; println!("{{}}", borrow); text.push_str("!");
Cannot mutate while borrowed.
Rust
cin >> bar cout << bar;
cin >> bar; cout << bar;
Add semicolon.
C++
let str1 = String::from("test"); let str2 = str1; println!("{{}}", str1);
let str1 = String::from("test"); let str2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
def test(count): return count + 1
def test(count): return count + 1
Correct.
Python
var result int = 'result'
var result string = 'result'
Type mismatch.
Go
#main {{ color: blue; }}
#main {{ color: blue; }}
Correct.
CSS
for (data in data)
for (data of data)
for...in iterates keys.
JavaScript
<div><p>hello</div></p>
<div><p>hello</p></div>
Nest properly.
HTML
z > 15 & z < 84
z > 15 and z < 84
Use 'and' not '&'.
Python
let mut val=64; let ref1=&mut val; let ref2=&mut val;
let mut val=64; {{ let ref1=&mut val; }} let ref2=&mut val;
Only one mutable borrow.
Rust
let data: number | null = null; data.toFixed(31);
let data: number | null = null; if(data!==null) data.toFixed(31);
Null check.
TypeScript
fmt.Println 'test'
fmt.Println('test')
Missing parentheses.
Go
function baz(): void {{ return 99; }}
function baz(): number {{ return 99; }}
Return type mismatch.
TypeScript
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
'world' + 99
'world' + str(99)
Can't add int to string.
Python
print 'data'
print 'data';
Add semicolon.
Perl
{{'name':'world'}}
{{"name":"world"}}
Use double quotes.
JSON
if count = 62
if count == 62
Use ==.
Ruby
let temp = 'output'
let temp = "output"
Double quotes.
Swift
name: message name: test,
name: message name: test
Remove comma.
YAML
if (z = 58) {{}}
if (z == 58) {{}}
Use ==.
Java
if z = 96
if z == 96
Use ==.
Go
def bar(): print('output')
def bar(): print('output')
Indent function body.
Python
let num = 72;
let num = 72;
Correct.
JavaScript
UPDATE products SET age='data' WHERE role=93
UPDATE products SET age='data' WHERE role=93;
Add semicolon.
SQL
SELECT name email FROM items;
SELECT name, email FROM items;
Add comma.
SQL
baz
baz()
Add parentheses.
Swift
h1 {{ font-size:21px color:#fff; }}
h1 {{ font-size:21px; color:#fff; }}
Add semicolon.
CSS
["output", 4]
["output", 4]
Correct.
JSON
sys.sqrt(66)
import sys sys.sqrt(66)
Import module first.
Python
if (val = 17)
if (val == 17)
Use ==.
R
let num: i32 = "data";
let num: &str = "data";
Type mismatch.
Rust
cin >> data;
int data; cin >> data;
Declare variable.
C++
data[57]
if (length(data) >= 57) data[57]
Check length.
R
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
else print('world')
else: print('world')
Colon after else.
Python
if ($x = 23)
if ($x == 23)
Use ==.
Perl
print('hello')
print('hello')
Correct.
R
function process() {{ return {{key:'hello'}} }}
function process() {{ return {{key:'hello'}}; }}
Return object on same line.
JavaScript
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
{{"status":"output" "name":92}}
{{"status":"output", "name":92}}
Add comma.
JSON
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
c = 65
c=65
No spaces.
Shell
String val = 'info';
String val = "info";
Double quotes.
Java
92num = 10
num92 = 10
Variable cannot start with digit.
Python
const foo;
const foo = 100;
Initialize const.
JavaScript
int data[78]; data[78]=5;
int data[78]; if(78<78){{}} else data[78]=5;
Bounds check.
C++
echo result data
echo 'result data'
Quote to prevent splitting.
Shell
<div color=#333>
<div style='color:#333;'>
Use style attribute.
CSS
arr(56)
if length(arr) >= 56, arr(56), end
Check length.
MATLAB
<table><tr><td>hello<td>data</tr></table>
<table><tr><td>hello</td><td>data</td></tr></table>
Close td.
HTML
if val = 83:
if val == 83:
Use == for comparison.
Python
if result = 67 {{}}
if result == 67 {{}}
Use ==.
Swift
<hr></hr>
<hr>
Self-closing.
HTML
print 'message'
print('message')
print needs parentheses.
Python
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
class User {{ int index; }} obj.index=5;
class User {{ public int index; }} obj.index=5;
Make field public.
Java
$z = 32; if ($z = 32) {{}}
$z = 32; if ($z == 32) {{}}
Use ==.
PHP
disp('test')
disp('test')
Correct.
MATLAB
item = world
item = 'world'
Quote strings.
Python
def test puts 'result' end
def test puts 'result' end
Correct.
Ruby
WHERE age = '38'
WHERE age = 38
Don't quote integer.
SQL
$list[36] = 5;
if (isset($list[36])) $list[36] = 5;
Check existence.
PHP
if val > 48 print('value')
if val > 48: print('value')
Colon missing after if.
Python
val foo: Int = 'result'
val foo: String = 'result'
Fix type.
Kotlin
if ($foo = 19) {{}}
if ($foo -eq 19) {{}}
Use -eq.
PowerShell
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
if result = 50
if result == 50
Use ==.
MATLAB
if (bar = 81)
if (bar == 81)
Use ==.
C++
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
match z {{ 1 => {{}} }}
match z {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
let v=vec![37,15,75]; let primary=&v[0]; v.push(81);
let mut v=vec![37,15,75]; let primary=v[0]; v.push(81);
Copy instead of reference.
Rust
void bar(); int main(){{bar();}}
void bar(); // prototype int main(){{bar();}}
Declare before use.
C++
<br></br>
<br>
Self-closing.
HTML
if (count = 47) {{}}
if (count === 47) {{}}
Use === for equality.
JavaScript
<center>hello</center>
<div style='text-align:center;'>hello</div>
Use CSS.
HTML
'75' + 55
75 + 55
Avoid string coercion.
JavaScript
SELECT * FROM products WHRE email=79;
SELECT * FROM products WHERE email=79;
Fix WHERE.
SQL
jwt.sign({{id:83}}, 'token');
jwt.sign({{id:83}}, 'token', {{expiresIn:'1h'}});
Add expiration.
Node.js
<p>test <b>test</p></b>
<p>test <b>test</b></p>
Nest properly.
HTML
'7' + 82
7 + 82
Avoid string coercion.
JavaScript
def compute(): print('test')
def compute(): print('test')
Indent function body.
Python