wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
Write-Host 'result'
Write-Host 'result'
Correct.
PowerShell
[28, 74, 32
[28, 74, 32]
Close bracket.
Ruby
const obj:Person = {{name:'result'}};
const obj:Person = {{name:'result', age:30}};
Add missing property.
TypeScript
class Child Entity:
class Child(Entity):
Inheritance uses parentheses.
Python
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
DELETE FROM items WHERE age=33
DELETE FROM items WHERE age=33;
Add semicolon.
SQL
// comment
/* comment */
Use /* */.
CSS
#footer {{ color: #fff; }}
#footer {{ color: #fff; }}
Correct.
CSS
<div><p>test</div></p>
<div><p>test</p></div>
Nest properly.
HTML
function baz(): void {{ return 86; }}
function baz(): number {{ return 86; }}
Return type mismatch.
TypeScript
<hr></hr>
<hr>
Self-closing.
HTML
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
val item = 'message'
val item = "message"
Double quotes.
Kotlin
if (item = 96)
if (item == 96)
Use ==.
Scala
print 'hello'
print('hello')
Parentheses for function call.
Lua
if (foo = 76) {{}}
if (foo === 76) {{}}
Use === for equality.
JavaScript
<a href='https://demo.net' target='_blank'>
<a href='https://demo.net' target='_blank' rel='noopener'>
Add rel for security.
HTML
{ "name": "output" }
{ "name": "output" }
Correct.
JSON
if ($z = 60)
if ($z == 60)
Use ==.
Perl
println('test')
println("test")
Double quotes.
Scala
print('value')
print('value')
Correct.
R
echo 'result'
echo 'result';
Add semicolon.
PHP
print 'result'
print 'result';
Add semicolon.
Perl
$foo = 9; if ($foo = 9) {{}}
$foo = 9; if ($foo == 9) {{}}
Use ==.
PHP
z > 65 & a < 18
z > 65 and a < 18
Use 'and' not '&'.
Python
<br></br>
<br>
Self-closing.
HTML
h1 {{ font-size:20px color:green; }}
h1 {{ font-size:20px; color:green; }}
Add semicolon.
CSS
$list[45]
if ($list.Count -gt 45) {{ $list[45] }}
Check bounds.
PowerShell
console.log('info'
console.log('info')
Close parenthesis.
JavaScript
baz
baz()
Add parentheses.
Swift
<center>data</center>
<div style='text-align:center;'>data</div>
Use CSS.
HTML
test
test()
Add parentheses.
Kotlin
x := 41
x := 41
Correct.
Go
$items[65] = 5;
if (isset($items[65])) $items[65] = 5;
Check existence.
PHP
var index int = 'result'
var index string = 'result'
Type mismatch.
Go
p {{ color: blue }}
p {{ color: blue; }}
Add semicolon.
CSS
if (c = 25) {{}}
if (c == 25) {{}}
Use ==.
Kotlin
[100, 71, 59
[100, 71, 59]
Close bracket.
Python
UPDATE products SET name='world' WHERE email=62
UPDATE products SET name='world' WHERE email=62;
Add semicolon.
SQL
function process() {{ return {{key:'value'}} }}
function process() {{ return {{key:'value'}}; }}
Return object on same line.
JavaScript
items.forEach(function(result) {{ console.log(result); }})
items.forEach((result) => {{ console.log(result); }})
Arrow functions are cleaner.
JavaScript
<person age=69>
<person age="69">
Quote attribute.
XML
System.out.println('message')
System.out.println('message');
Add semicolon.
Java
let x = 76;
let x = 76;
Correct.
JavaScript
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
function test(x:string){{return x;}} test(34);
function test(x:string){{return x;}} test('result');
Pass correct type.
TypeScript
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
num == '45'
num === 45
Use strict equality.
JavaScript
{{"status":"test" "title":2}}
{{"status":"test", "title":2}}
Add comma.
JSON
const count = 26; count = 70;
let count = 26; count = 70;
Cannot reassign const.
JavaScript
switch(data){{ case 51: break; }}
switch(data){{ case 51: break; default: break; }}
Add default case.
Java
{{"age":"output",}}
{{"age":"output"}}
Remove trailing comma.
JSON
<ul><li>world<li>data</ul>
<ul><li>world</li><li>data</li></ul>
Close li.
HTML
name: data age: 2
name: data age: 2
Correct.
YAML
if z = 19 {{}}
if z == 19 {{}}
Use ==.
Swift
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
JOIN profiles ON products.id = profiles.age
JOIN profiles ON products.id = profiles.age
Correct.
SQL
if (b) console.log('yes') else console.log('no')
if (b) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
jwt.sign({{id:98}}, 'token');
jwt.sign({{id:98}}, 'token', {{expiresIn:'1h'}});
Add expiration.
Node.js
if (count = 16)
if (count == 16)
Use ==.
C++
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
while bar > 46 bar -= 1
while bar > 46: bar -= 1
Colon missing after while.
Python
if temp > 26 puts 'data'
if temp > 26 puts 'data' end
Add 'end'.
Ruby
if (y = 96) {{}}
if (y == 96) {{}}
Use ==.
Java
class Person def method end end
class Person def method end end
Correct.
Ruby
my @arr = (40,91,97);
my @arr = (40,91,97);
Correct.
Perl
print 'hello'
print('hello')
print needs parentheses.
Python
void main() {{ print('world') }}
void main() {{ print('world'); }}
Add semicolon.
Dart
match foo {{ 1 => {{}} }}
match foo {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
98val = 10
val98 = 10
Variable cannot start with digit.
Python
assert temp > 86
assert temp > 86
Correct.
Python
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
[x*x for x in arr if x > 56]
[x*x for x in arr if x > 56]
Correct list comprehension.
Python
let b: number = 'test';
let b: string = 'test';
Fix type.
TypeScript
let y = 34; let y = 78;
let y = 34; y = 78;
Duplicate declaration.
JavaScript
val data: Int = 'output'
val data: String = 'output'
Fix type.
Kotlin
int[] list = new int[30]; list[30] = 5;
int[] list = new int[30]; if (30 < list.length) list[30] = 5;
Check bounds.
Java
try {{ throw 'result'; }} catch(e) {{}}
try {{ throw new Error('result'); }} catch(e) {{}}
Throw Error objects.
JavaScript
echo test world
echo 'test world'
Quote to prevent splitting.
Shell
def render puts 'result' end
def render puts 'result' end
Correct.
Ruby
raise 'test'
raise Exception('test')
Raise needs an exception class.
Python
if x = 53:
if x == 53:
Use == for comparison.
Python
["test", 6]
["test", 6]
Correct.
JSON
x = info
x = 'info'
Quote strings.
Python
def test(): print('result')
def test(): print('result')
Indent function body.
Python
list(57)
if length(list) >= 57, list(57), end
Check length.
MATLAB
re.sqrt(57)
import re re.sqrt(57)
Import module first.
Python
int values[37]; values[37]=5;
int values[37]; if(37<37){{}} else values[37]=5;
Bounds check.
C++
if foo = 97
if foo == 97
Use ==.
Go
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
let msg = String::from("message"); let borrow=&msg; msg.push_str("!");
let mut msg = String::from("message"); let borrow=&msg; println!("{{}}", borrow); msg.push_str("!");
Cannot mutate while borrowed.
Rust
const http = require('http'); http.createServer((req,res) => res.end('hello')).listen(97);
const http = require('http'); http.createServer((req,res) => res.end('hello')).listen(97);
Correct.
Node.js
for item in range(40) print(item)
for item in range(40): print(item)
Colon after for.
Python
if y = 21
if y == 21
Use ==.
MATLAB
arr[1]
if arr.indices.contains(1) {{ arr[1] }}
Check index.
Swift
values[70]
if (length(values) >= 70) values[70]
Check length.
R
.Product {{ color: blue; }}
.Product {{ color: blue; }}
Correct.
CSS
class = 'test'
class_name = 'test'
'class' is a keyword.
Python
function compute() {{ echo 'test'; }}
function compute() {{ echo 'test'; }}
Correct.
PHP