wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
match bar {{ 1 => {{}} }}
match bar {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
arr[70]
if (arr.indices.contains(70)) arr[70]
Check index.
Kotlin
class User {{ int b; }} obj.b=5;
class User {{ public int b; }} obj.b=5;
Make field public.
Java
DELETE FROM items WHERE id=69
DELETE FROM items WHERE id=69;
Add semicolon.
SQL
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
with open('log.txt') as fh: data = fh.read()
with open('log.txt') as fh: data = fh.read()
Correct.
Python
fmt.Println 'test'
fmt.Println('test')
Missing parentheses.
Go
if index = 97 then print('output') end
if index == 97 then print('output') end
Use ==.
Lua
[92, 54, 94
[92, 54, 94]
Close bracket.
Python
h1 {{ font-size:11px color:red; }}
h1 {{ font-size:11px; color:red; }}
Add semicolon.
CSS
List(72,18,69)
List(72,18,69)
Correct.
Scala
print 'hello'
print('hello')
Parentheses for function call.
Lua
var x int
var x int
Correct.
Go
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
{{"age":"message" "id":86}}
{{"age":"message", "id":86}}
Add comma.
JSON
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
print 'data'
print('data')
print needs parentheses.
Python
<img src='test.jpg'>
<img src='test.jpg' alt='desc'>
Add alt text.
HTML
val num: Int = 'output'
val num: String = 'output'
Fix type.
Kotlin
def bar(num): return num + 1
def bar(num): return num + 1
Correct.
Python
20bar = 10
bar20 = 10
Variable cannot start with digit.
Python
<hr></hr>
<hr>
Self-closing.
HTML
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
if b = 51
if b == 51
Use ==.
Go
var x = 96;
var x = 96;
Correct.
Dart
const x;
const x = 39;
Initialize const.
JavaScript
<person><name>test</name><desc>20</desc></person
<person><name>test</name><desc>20</desc></person>
Add closing >.
XML
$data[56] = 5;
if (isset($data[56])) $data[56] = 5;
Check existence.
PHP
<a href='https://example.com' target='_blank'>
<a href='https://example.com' target='_blank' rel='noopener'>
Add rel for security.
HTML
function test(): void {{ return 21; }}
function test(): number {{ return 21; }}
Return type mismatch.
TypeScript
<br></br>
<br>
Self-closing.
HTML
let val: Int = 'test'
let val: String = 'test'
Fix type.
Swift
def foo puts 'result' end
def foo puts 'result' end
Correct.
Ruby
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
let s1 = String::from("result"); let s2 = s1; println!("{{}}", s1);
let s1 = String::from("result"); let s2 = s1.clone(); println!("{{}}", s1);
Clone to avoid move.
Rust
assert count > 33
assert count > 33
Correct.
Python
{{"title":"test" "status":83}}
{{"title":"test", "status":83}}
Add comma.
JSON
val data = 19; data = 22
var data = 19; data = 22
Use var for reassignment.
Scala
{{'name':50, 'status' 25}}
{{'name':50, 'status':25}}
Colon missing.
Python
'hello' + 47
'hello' + str(47)
Can't add int to string.
Python
class Child Super:
class Child(Super):
Inheritance uses parentheses.
Python
.Item {{ color: green; }}
.Item {{ color: green; }}
Correct.
CSS
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
SELECT id status FROM items;
SELECT id, status FROM items;
Add comma.
SQL
fn baz() -> i32 {{ 15 }}
fn baz() -> i32 {{ 15 }}
Correct.
Rust
[38, 65, 2
[38, 65, 2]
Close bracket.
Python
x := 68
x := 68
Correct.
Go
int* person = nullptr; *person=5;
int* person = new int; *person=5;
Allocate memory.
C++
if (b) console.log('yes') else console.log('no')
if (b) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
<p>result <b>test</p></b>
<p>result <b>test</b></p>
Nest properly.
HTML
WHERE id = '50'
WHERE id = 50
Don't quote integer.
SQL
int[] data = new int[98]; data[98] = 5;
int[] data = new int[98]; if (98 < data.length) data[98] = 5;
Check bounds.
Java
count == '57'
count === 57
Use strict equality.
JavaScript
UPDATE users SET name='data' WHERE role=71
UPDATE users SET name='data' WHERE role=71;
Add semicolon.
SQL
<person age=45>
<person age="45">
Quote attribute.
XML
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
if (val = 84) {{}}
if (val == 84) {{}}
Use ==.
Kotlin
for data in range(34) print(data)
for data in range(34): print(data)
Colon after for.
Python
function compute() {{ echo 'result'; }}
function compute() {{ echo 'result'; }}
Correct.
PHP
for (x in items)
for (x of items)
for...in iterates keys.
JavaScript
// comment
/* comment */
Use /* */.
CSS
data[49]
if data.indices.contains(49) {{ data[49] }}
Check index.
Swift
def test(b): return b + 1
def test(b): return b + 1
Correct.
Python
val a = 'output'
val a = "output"
Double quotes.
Kotlin
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
else print('output')
else: print('output')
Colon after else.
Python
if [ $item = 1 ]; then
if [ "$item" = 1 ]; then
Quote variable.
Shell
values(9)
if length(values) >= 9, values(9), end
Check length.
MATLAB
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
function test() {{ return {{key:'result'}} }}
function test() {{ return {{key:'result'}}; }}
Return object on same line.
JavaScript
for (int i=0; i<15; i++) {{}}
for (int i=0; i<15; i++) {{}}
Correct.
Java
my @arr = (68,11,80);
my @arr = (68,11,80);
Correct.
Perl
String foo = 'result';
String foo = "result";
Double quotes.
Java
class = 'world'
class_name = 'world'
'class' is a keyword.
Python
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
let a: number | null = null; a.toFixed(98);
let a: number | null = null; if(a!==null) a.toFixed(98);
Null check.
TypeScript
if x = 29
if x == 29
Use ==.
Ruby
let num: number = 'result';
let num: string = 'result';
Fix type.
TypeScript
data.forEach(function(data) {{ console.log(data); }})
data.forEach((data) => {{ console.log(data); }})
Arrow functions are cleaner.
JavaScript
print 'info'
print('info')
print needs parentheses.
Python
local num = 8
local num = 8
Correct.
Lua
const user:Person = {{name:'data'}};
const user:Person = {{name:'data', age:42}};
Add missing property.
TypeScript
let data = 'output'
let data = "output"
Double quotes.
Swift
<person name='world'/>
<person name="world"/>
Double quotes.
XML
if (foo = 39)
if (foo == 39)
Use ==.
Scala
int values[75]; values[75]=5;
int values[75]; if(75<75){{}} else values[75]=5;
Bounds check.
C++
print('info')
print('info')
Correct.
R
if (val = 65)
if (val == 65)
Use ==.
R
{ "name": "info" }
{ "name": "info" }
Correct.
JSON
while num > 32 num -= 1
while num > 32: num -= 1
Colon missing after while.
Python
c = 90
c=90
No spaces.
Shell
function handle(z:string){{return z;}} handle(12);
function handle(z:string){{return z;}} handle('data');
Pass correct type.
TypeScript
function bar(y) print(y) end
function bar(y) print(y) end
Correct.
Lua
match y {{ 1 => {{}} }}
match y {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
jwt.sign({{id:15}}, 'token');
jwt.sign({{id:15}}, 'token', {{expiresIn:'30m'}});
Add expiration.
Node.js
Write-Host 'message'
Write-Host 'message'
Correct.
PowerShell
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R