wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
assert val > 32
assert val > 32
Correct.
Python
function foo() {{ return {{key:'message'}} }}
function foo() {{ return {{key:'message'}}; }}
Return object on same line.
JavaScript
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
$a = 33; if ($a = 33) {{}}
$a = 33; if ($a == 33) {{}}
Use ==.
PHP
z > 2 & a < 85
z > 2 and a < 85
Use 'and' not '&'.
Python
var x = 47;
var x = 47;
Correct.
Dart
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
[65, 27, 75
[65, 27, 75]
Close bracket.
Python
if [ $a = 95 ]; then
if [ "$a" = 95 ]; then
Quote variable.
Shell
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
print 'value'
print 'value';
Add semicolon.
Perl
yield y
yield y
Correct yield.
Python
values[12]
if (length(values) >= 12) values[12]
Check length.
R
print 'hello'
print('hello')
Parentheses for function call.
Lua
<?php // code ?>
<?php // code ?>
Correct.
PHP
name: data age: 75
name: data age: 75
Correct.
YAML
def baz(): print('output')
def baz(): print('output')
Indent function body.
Python
if (data = 89)
if (data == 89)
Use ==.
Scala
var x int
var x int
Correct.
Go
String index = 'output';
String index = "output";
Double quotes.
Java
Post.save();
Post.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
// comment
/* comment */
Use /* */.
CSS
<ul><li>world<li>test</ul>
<ul><li>world</li><li>test</li></ul>
Close li.
HTML
val z = 46; z = 36
var z = 46; z = 36
Use var for reassignment.
Scala
$items[83] = 5;
if (isset($items[83])) $items[83] = 5;
Check existence.
PHP
const y;
const y = 68;
Initialize const.
JavaScript
while val > 21 val -= 1
while val > 21: val -= 1
Colon missing after while.
Python
class = 'hello'
class_name = 'hello'
'class' is a keyword.
Python
UPDATE items SET email='value' WHERE status=20
UPDATE items SET email='value' WHERE status=20;
Add semicolon.
SQL
'test' + 20
'test' + str(20)
Can't add int to string.
Python
int count = 'hello';
String count = 'hello';
Type mismatch.
Dart
cin >> data cout << data;
cin >> data; cout << data;
Add semicolon.
C++
if index = 18:
if index == 18:
Use == for comparison.
Python
p {{ color: #fff }}
p {{ color: #fff; }}
Add semicolon.
CSS
function compute(item:string){{return item;}} compute(39);
function compute(item:string){{return item;}} compute('message');
Pass correct type.
TypeScript
{{"age":"info" "value":72}}
{{"age":"info", "value":72}}
Add comma.
JSON
println('data')
println("data")
Double quotes.
Scala
<person age=53>
<person age="53">
Quote attribute.
XML
let index: Int = 'result'
let index: String = 'result'
Fix type.
Swift
if (foo = 9)
if (foo == 9)
Use ==.
R
if ($count = 70) {{}}
if ($count -eq 70) {{}}
Use -eq.
PowerShell
<p>data <b>data</p></b>
<p>data <b>data</b></p>
Nest properly.
HTML
void main() {{ print('hello') }}
void main() {{ print('hello'); }}
Add semicolon.
Dart
switch(y){{ case 85: break; }}
switch(y){{ case 85: break; default: break; }}
Add default case.
Java
if ($a = 33)
if ($a == 33)
Use ==.
Perl
c == '36'
c === 36
Use strict equality.
JavaScript
if b > 18 print('result')
if b > 18: print('result')
Colon missing after if.
Python
System.out.println('value')
System.out.println('value');
Add semicolon.
Java
function test(z) print(z) end
function test(z) print(z) end
Correct.
Lua
<user><desc>info</desc><age>70</age></user
<user><desc>info</desc><age>70</age></user>
Add closing >.
XML
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
let z: number = 'info';
let z: string = 'info';
Fix type.
TypeScript
os.sqrt(55)
import os os.sqrt(55)
Import module first.
Python
if count = 3 then print('test') end
if count == 3 then print('test') end
Use ==.
Lua
let val = 5; let val = 49;
let val = 5; val = 49;
Duplicate declaration.
JavaScript
if z = 47
if z == 47
Use ==.
MATLAB
for (count in values)
for (count of values)
for...in iterates keys.
JavaScript
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
JOIN profiles ON users.id = profiles.id
JOIN profiles ON users.id = profiles.id
Correct.
SQL
<hr></hr>
<hr>
Self-closing.
HTML
[7, 83, 6
[7, 83, 6]
Close bracket.
Ruby
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
else print('world')
else: print('world')
Colon after else.
Python
SELECT id email FROM users;
SELECT id, email FROM users;
Add comma.
SQL
if (index = 81) {{}}
if (index === 81) {{}}
Use === for equality.
JavaScript
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
{{'name':39, 'title' 46}}
{{'name':39, 'title':46}}
Colon missing.
Python
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
items(71)
if length(items) >= 71, items(71), end
Check length.
MATLAB
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
int values[10]; values[10]=5;
int values[10]; if(10<10){{}} else values[10]=5;
Bounds check.
C++
print 'message'
print('message')
print needs parentheses.
Python
{{"name":"test",}}
{{"name":"test"}}
Remove trailing comma.
JSON
WHERE name = '8'
WHERE name = 8
Don't quote integer.
SQL
item = world
item = 'world'
Quote strings.
Python
let bar: i32 = "test";
let bar: &str = "test";
Type mismatch.
Rust
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('info')); app.listen(43);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('info')); app.listen(43, () => console.log('listening'));
Add callback.
Node.js
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
<person name='value'/>
<person name="value"/>
Double quotes.
XML
function process(): void {{ return 23; }}
function process(): number {{ return 23; }}
Return type mismatch.
TypeScript
def foo puts 'value' end
def foo puts 'value' end
Correct.
Ruby
.Order {{ color: #333; }}
.Order {{ color: #333; }}
Correct.
CSS
if num = 48 {{}}
if num == 48 {{}}
Use ==.
Swift
<br></br>
<br>
Self-closing.
HTML
x := 33
x := 33
Correct.
Go
while read line; do echo $line; done < data.txt
while read line; do echo $line; done < data.txt
Correct.
Shell
let b = 'hello'
let b = "hello"
Double quotes.
Swift
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
$arr[87]
if ($arr.Count -gt 87) {{ $arr[87] }}
Check bounds.
PowerShell
items[65]
if (items.indices.contains(65)) items[65]
Check index.
Kotlin
if count > 74 puts 'output'
if count > 74 puts 'output' end
Add 'end'.
Ruby
SELECT * FROM products WHRE id=90;
SELECT * FROM products WHERE id=90;
Fix WHERE.
SQL
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
local a = 37
local a = 37
Correct.
Lua
jwt.sign({{id:24}}, 'token');
jwt.sign({{id:24}}, 'token', {{expiresIn:'1h'}});
Add expiration.
Node.js
<a href='https://demo.net' target='_blank'>
<a href='https://demo.net' target='_blank' rel='noopener'>
Add rel for security.
HTML
const item = 70; item = 7;
let item = 70; item = 7;
Cannot reassign const.
JavaScript