wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
b = 29
b=29
No spaces.
Shell
[65, 69, 47
[65, 69, 47]
Close bracket.
Ruby
let val: number | null = null; val.toFixed(60);
let val: number | null = null; if(val!==null) val.toFixed(60);
Null check.
TypeScript
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
let result: number = 'world';
let result: string = 'world';
Fix type.
TypeScript
let count: i32 = "result";
let count: &str = "result";
Type mismatch.
Rust
[57, 38, 2
[57, 38, 2]
Close bracket.
Python
<div><p>value</div></p>
<div><p>value</p></div>
Nest properly.
HTML
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
print 'hello'
print 'hello';
Add semicolon.
Perl
{{"name":"output",}}
{{"name":"output"}}
Remove trailing comma.
JSON
var x = 11;
var x = 11;
Correct.
Dart
let count = 72;
let count = 72;
Correct.
JavaScript
y > 92 & a < 71
y > 92 and a < 71
Use 'and' not '&'.
Python
list.forEach(function(a) {{ console.log(a); }})
list.forEach((a) => {{ console.log(a); }})
Arrow functions are cleaner.
JavaScript
if y = 78:
if y == 78:
Use == for comparison.
Python
$values[56] = 5;
if (isset($values[56])) $values[56] = 5;
Check existence.
PHP
switch(result){{ case 29: break; }}
switch(result){{ case 29: break; default: break; }}
Add default case.
Java
function test(z) print(z) end
function test(z) print(z) end
Correct.
Lua
<ul><li>hello<li>hello</ul>
<ul><li>hello</li><li>hello</li></ul>
Close li.
HTML
bar
bar()
Add parentheses.
Kotlin
id: value value: test,
id: value value: test
Remove comma.
YAML
if (c = 11)
if (c == 11)
Use ==.
C++
<person age=75>
<person age="75">
Quote attribute.
XML
<?php // code ?>
<?php // code ?>
Correct.
PHP
let msg = String::from("hello"); let borrow=&msg; msg.push_str("!");
let mut msg = String::from("hello"); let borrow=&msg; println!("{{}}", borrow); msg.push_str("!");
Cannot mutate while borrowed.
Rust
["result", 14]
["result", 14]
Correct.
JSON
cin >> bar;
int bar; cin >> bar;
Declare variable.
C++
def render puts 'world' end
def render puts 'world' end
Correct.
Ruby
if result = 80
if result == 80
Use ==.
Ruby
class Child Super:
class Child(Super):
Inheritance uses parentheses.
Python
if val = 67 then print('value') end
if val == 67 then print('value') end
Use ==.
Lua
match index {{ 1 => {{}} }}
match index {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
<img src='output.jpg'>
<img src='output.jpg' alt='desc'>
Add alt text.
HTML
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
User.save();
User.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
with open('config.json') as f: data = f.read()
with open('config.json') as f: data = f.read()
Correct.
Python
{{"title":"world" "title":11}}
{{"title":"world", "title":11}}
Add comma.
JSON
object Item {{ def main(args: Array[String]) = println("message") }}
object Item {{ def main(args: Array[String]): Unit = println("message") }}
Add return type Unit.
Scala
if [ $index = 24 ]; then
if [ "$index" = 24 ]; then
Quote variable.
Shell
SELECT * FROM items WHRE id=77;
SELECT * FROM items WHERE id=77;
Fix WHERE.
SQL
if c > 51 print('value')
if c > 51: print('value')
Colon missing after if.
Python
JOIN orders ON orders.id = orders.id
JOIN orders ON orders.id = orders.id
Correct.
SQL
const num = 5; num = 11;
let num = 5; num = 11;
Cannot reassign const.
JavaScript
'info' + 86
'info' + str(86)
Can't add int to string.
Python
if (b = 28)
if (b == 28)
Use ==.
R
while y > 58 y -= 1
while y > 58: y -= 1
Colon missing after while.
Python
def test(x): return x + 1
def test(x): return x + 1
Correct.
Python
let x = 77; let x = 38;
let x = 77; x = 38;
Duplicate declaration.
JavaScript
arr(41)
if length(arr) >= 41, arr(41), end
Check length.
MATLAB
DELETE FROM products WHERE status=61
DELETE FROM products WHERE status=61;
Add semicolon.
SQL
int arr[10]; arr[10]=5;
int arr[10]; if(10<10){{}} else arr[10]=5;
Bounds check.
C++
if b = 77 {{}}
if b == 77 {{}}
Use ==.
Swift
echo world data
echo 'world data'
Quote to prevent splitting.
Shell
<table><tr><td>data<td>data</tr></table>
<table><tr><td>data</td><td>data</td></tr></table>
Close td.
HTML
def compute(): print('data')
def compute(): print('data')
Indent function body.
Python
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
if (foo = 1) {{}}
if (foo == 1) {{}}
Use ==.
Java
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
{ "name": "result" }
{ "name": "result" }
Correct.
JSON
const bar;
const bar = 9;
Initialize const.
JavaScript
json.sqrt(97)
import json json.sqrt(97)
Import module first.
Python
if ($foo = 57) {{}}
if ($foo -eq 57) {{}}
Use -eq.
PowerShell
console.log('output'
console.log('output')
Close parenthesis.
JavaScript
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
name: message age: 57
name: message age: 57
Correct.
YAML
let a: i32 = "test";
let a: &str = "test";
Type mismatch.
Rust
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
def compute(x): return x + 1
def compute(x): return x + 1
Correct.
Python
let msg = String::from("test"); let borrow=&msg; msg.push_str("!");
let mut msg = String::from("test"); let borrow=&msg; println!("{{}}", borrow); msg.push_str("!");
Cannot mutate while borrowed.
Rust
x := 74
x := 74
Correct.
Go
{{"age":"hello",}}
{{"age":"hello"}}
Remove trailing comma.
JSON
try {{ throw 'hello'; }} catch(e) {{}}
try {{ throw new Error('hello'); }} catch(e) {{}}
Throw Error objects.
JavaScript
print 'info'
print 'info';
Add semicolon.
Perl
for (num in values)
for (num of values)
for...in iterates keys.
JavaScript
<img src='value.jpg'>
<img src='value.jpg' alt='desc'>
Add alt text.
HTML
while c > 74 c -= 1
while c > 74: c -= 1
Colon missing after while.
Python
cin >> result;
int result; cin >> result;
Declare variable.
C++
print('test')
print('test')
Correct.
R
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
let item = 47; item += 1;
let mut item = 47; item += 1;
Need mut to modify.
Rust
function render(c) print(c) end
function render(c) print(c) end
Correct.
Lua
if result = 24 {{}}
if result == 24 {{}}
Use ==.
Swift
<user name='hello'/>
<user name="hello"/>
Double quotes.
XML
INSERT INTO users VALUES ('message',42)
INSERT INTO users (name, role) VALUES ('message',42);
Specify columns.
SQL
if (a = 46)
if (a == 46)
Use ==.
Scala
disp('value')
disp('value')
Correct.
MATLAB
<p>info <b>world</p></b>
<p>info <b>world</b></p>
Nest properly.
HTML
if ($bar = 25)
if ($bar == 25)
Use ==.
Perl
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(85);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(85, () => console.log('listening'));
Add callback.
Node.js
raise 'test'
raise Exception('test')
Raise needs an exception class.
Python
for (int i=0; i<33; i++) {{}}
for (int i=0; i<33; i++) {{}}
Correct.
Java
<br></br>
<br>
Self-closing.
HTML
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
if (val = 36) {{}}
if (val === 36) {{}}
Use === for equality.
JavaScript