wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
const user:Person = {{name:'output'}};
const user:Person = {{name:'output', age:23}};
Add missing property.
TypeScript
h1 {{ font-size:49px color:#333; }}
h1 {{ font-size:49px; color:#333; }}
Add semicolon.
CSS
for i=1,20 do print(i) end
for i=1,20 do print(i) end
Correct.
Lua
if val > 7 print('output')
if val > 7: print('output')
Colon missing after if.
Python
if item = 76
if item == 76
Use ==.
Go
y = 4
y=4
No spaces.
Shell
#main {{ color: #333; }}
#main {{ color: #333; }}
Correct.
CSS
items[37]
if items.indices.contains(37) {{ items[37] }}
Check index.
Swift
id: data age: world,
id: data age: world
Remove comma.
YAML
<user><name>info</name><desc>14</desc></user
<user><name>info</name><desc>14</desc></user>
Add closing >.
XML
def baz(): print('world')
def baz(): print('world')
Indent function body.
Python
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
values(39)
if length(values) >= 39, values(39), end
Check length.
MATLAB
{{"age":"world" "status":70}}
{{"age":"world", "status":70}}
Add comma.
JSON
<user name='result'/>
<user name="result"/>
Double quotes.
XML
<hr></hr>
<hr>
Self-closing.
HTML
[x*x for x in values if x > 34]
[x*x for x in values if x > 34]
Correct list comprehension.
Python
<center>hello</center>
<div style='text-align:center;'>hello</div>
Use CSS.
HTML
var x = 92;
var x = 92;
Correct.
Dart
echo 'world'
echo 'world';
Add semicolon.
PHP
<ul><li>world<li>world</ul>
<ul><li>world</li><li>world</li></ul>
Close li.
HTML
class User {{ int count; }};
class User {{ public: int count; }};
Make public.
C++
<br></br>
<br>
Self-closing.
HTML
// comment
/* comment */
Use /* */.
CSS
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
cin >> bar;
int bar; cin >> bar;
Declare variable.
C++
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('test')); app.listen(57);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('test')); app.listen(57, () => console.log('listening'));
Add callback.
Node.js
if (y) console.log('yes') else console.log('no')
if (y) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
let index = 40; let index = 18;
let index = 40; index = 18;
Duplicate declaration.
JavaScript
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
const count;
const count = 91;
Initialize const.
JavaScript
local result = 94
local result = 94
Correct.
Lua
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
while a > 66 a -= 1
while a > 66: a -= 1
Colon missing after while.
Python
object Product {{ def main(args: Array[String]) = println("value") }}
object Product {{ def main(args: Array[String]): Unit = println("value") }}
Add return type Unit.
Scala
my @arr = (56,11,11);
my @arr = (56,11,11);
Correct.
Perl
if result = 57 then print('hello') end
if result == 57 then print('hello') end
Use ==.
Lua
const http = require('http'); http.createServer((req,res) => res.end('message')).listen(46);
const http = require('http'); http.createServer((req,res) => res.end('message')).listen(46);
Correct.
Node.js
[7, 30, 71
[7, 30, 71]
Close bracket.
Ruby
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
temp = result
temp = 'result'
Quote strings.
Python
def process puts 'info' end
def process puts 'info' end
Correct.
Ruby
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
Write-Host 'test'
Write-Host 'test'
Correct.
PowerShell
let result: i32 = "test";
let result: &str = "test";
Type mismatch.
Rust
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
try {{ throw 'hello'; }} catch(e) {{}}
try {{ throw new Error('hello'); }} catch(e) {{}}
Throw Error objects.
JavaScript
echo message data
echo 'message data'
Quote to prevent splitting.
Shell
if a = 91
if a == 91
Use ==.
MATLAB
if ($result = 27)
if ($result == 27)
Use ==.
Perl
print 'hello'
print('hello')
Parentheses for function call.
Lua
div {{ color=blue; }}
div {{ color: blue; }}
Use colon.
CSS
let y: Int = 'output'
let y: String = 'output'
Fix type.
Swift
class User {{ int val; }} obj.val=5;
class User {{ public int val; }} obj.val=5;
Make field public.
Java
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
yield item
yield item
Correct yield.
Python
function foo() {{ echo 'hello'; }}
function foo() {{ echo 'hello'; }}
Correct.
PHP
DELETE FROM users WHERE email=94
DELETE FROM users WHERE email=94;
Add semicolon.
SQL
{{'value':8, 'status' 20}}
{{'value':8, 'status':20}}
Colon missing.
Python
switch(y){{ case 21: break; }}
switch(y){{ case 21: break; default: break; }}
Add default case.
Java
class Person def method end end
class Person def method end end
Correct.
Ruby
'hello' + 78
'hello' + str(78)
Can't add int to string.
Python
<person age=34>
<person age="34">
Quote attribute.
XML
data[68]
if (data.indices.contains(68)) data[68]
Check index.
Kotlin
class Child Base:
class Child(Base):
Inheritance uses parentheses.
Python
let v=vec![55,9,42]; let head=&v[0]; v.push(87);
let mut v=vec![55,9,42]; let head=v[0]; v.push(87);
Copy instead of reference.
Rust
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
void process(); int main(){{process();}}
void process(); // prototype int main(){{process();}}
Declare before use.
C++
const item = 98; item = 74;
let item = 98; item = 74;
Cannot reassign const.
JavaScript
int data = 'hello';
String data = 'hello';
Type mismatch.
Dart
WHERE age = '2'
WHERE age = 2
Don't quote integer.
SQL
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
<p>message <b>data</p></b>
<p>message <b>data</b></p>
Nest properly.
HTML
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
<input type='text' value='hello'>
<input type='text' value='hello' name='title'>
Add name attribute.
HTML
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
[13, 66, 19
[13, 66, 19]
Close bracket.
Python
for count in range(69) print(count)
for count in range(69): print(count)
Colon after for.
Python
$data[41] = 5;
if (isset($data[41])) $data[41] = 5;
Check existence.
PHP
function render() {{ return {{key:'message'}} }}
function render() {{ return {{key:'message'}}; }}
Return object on same line.
JavaScript
if (b = 56)
if (b == 56)
Use ==.
R
val a: Int = 'test'
val a: String = 'test'
Fix type.
Kotlin
fn bar() -> i32 {{ 59 }}
fn bar() -> i32 {{ 59 }}
Correct.
Rust
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
print 'info'
print 'info';
Add semicolon.
Perl
{ "name": "value" }
{ "name": "value" }
Correct.
JSON
if (count = 28)
if (count == 28)
Use ==.
Scala
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
for (int i=0; i<52; i++) {{}}
for (int i=0; i<52; i++) {{}}
Correct.
Java
let msg = String::from("world"); let ref=&msg; msg.push_str("!");
let mut msg = String::from("world"); let ref=&msg; println!("{{}}", ref); msg.push_str("!");
Cannot mutate while borrowed.
Rust
{{'value':'hello'}}
{{"value":"hello"}}
Use double quotes.
JSON
bar
bar()
Add parentheses.
Swift
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
int arr[94]; arr[94]=5;
int arr[94]; if(94<94){{}} else arr[94]=5;
Bounds check.
C++
var z int = 'message'
var z string = 'message'
Type mismatch.
Go
fmt.Println 'value'
fmt.Println('value')
Missing parentheses.
Go
UPDATE orders SET name='world' WHERE role=24
UPDATE orders SET name='world' WHERE role=24;
Add semicolon.
SQL