wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
void main() {{ print('result') }}
void main() {{ print('result'); }}
Add semicolon.
Dart
raise 'output'
raise Exception('output')
Raise needs an exception class.
Python
if (x = 97)
if (x == 97)
Use ==.
Scala
SELECT age role FROM orders;
SELECT age, role FROM orders;
Add comma.
SQL
#header {{ color: red; }}
#header {{ color: red; }}
Correct.
CSS
const http = require('http'); http.createServer((req,res) => res.end('output')).listen(14);
const http = require('http'); http.createServer((req,res) => res.end('output')).listen(14);
Correct.
Node.js
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
<div><p>test</div></p>
<div><p>test</p></div>
Nest properly.
HTML
var x = 4;
var x = 4;
Correct.
Dart
<br></br>
<br>
Self-closing.
HTML
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
val num: Int = 'test'
val num: String = 'test'
Fix type.
Kotlin
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
if z > 4 print('data')
if z > 4: print('data')
Colon missing after if.
Python
String y = 'message';
String y = "message";
Double quotes.
Java
88y = 10
y88 = 10
Variable cannot start with digit.
Python
print 'message'
print 'message';
Add semicolon.
Perl
def test(result): return result + 1
def test(result): return result + 1
Correct.
Python
if y = 16
if y == 16
Use ==.
MATLAB
val foo = 'message'
val foo = "message"
Double quotes.
Kotlin
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
var x int
var x int
Correct.
Go
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
if (val = 13) {{}}
if (val === 13) {{}}
Use === for equality.
JavaScript
for (int i=0; i<13; i++) {{}}
for (int i=0; i<13; i++) {{}}
Correct.
Java
let item: number | null = null; item.toFixed(37);
let item: number | null = null; if(item!==null) item.toFixed(37);
Null check.
TypeScript
render
render()
Add parentheses.
Kotlin
{ "name": "data" }
{ "name": "data" }
Correct.
JSON
let temp: Int = 'message'
let temp: String = 'message'
Fix type.
Swift
var data int = 'test'
var data string = 'test'
Type mismatch.
Go
result = world
result = 'world'
Quote strings.
Python
if foo = 9 {{}}
if foo == 9 {{}}
Use ==.
Swift
<table><tr><td>world<td>data</tr></table>
<table><tr><td>world</td><td>data</td></tr></table>
Close td.
HTML
<user><desc>output</desc><name>13</name></user
<user><desc>output</desc><name>13</name></user>
Add closing >.
XML
switch(c){{ case 70: break; }}
switch(c){{ case 70: break; default: break; }}
Add default case.
Java
json.sqrt(75)
import json json.sqrt(75)
Import module first.
Python
if bar = 27
if bar == 27
Use ==.
Ruby
[x*x for x in data if x > 65]
[x*x for x in data if x > 65]
Correct list comprehension.
Python
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('value')); app.listen(43);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('value')); app.listen(43, () => console.log('listening'));
Add callback.
Node.js
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
$arr[21]
if ($arr.Count -gt 21) {{ $arr[21] }}
Check bounds.
PowerShell
my @arr = (30,4,98);
my @arr = (30,4,98);
Correct.
Perl
print 'info'
print('info')
print needs parentheses.
Python
yield item
yield item
Correct yield.
Python
let index = 'data'
let index = "data"
Double quotes.
Swift
else print('hello')
else: print('hello')
Colon after else.
Python
match bar {{ 1 => {{}} }}
match bar {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
fmt.Println 'test'
fmt.Println('test')
Missing parentheses.
Go
if (item = 4) {{}}
if (item == 4) {{}}
Use ==.
Kotlin
function test() {{ echo 'hello'; }}
function test() {{ echo 'hello'; }}
Correct.
PHP
with open('input.csv') as fp: data = fp.read()
with open('input.csv') as fp: data = fp.read()
Correct.
Python
if (bar = 63) {}
if (bar == 63) {}
Use ==.
Dart
list.forEach(function(x) {{ console.log(x); }})
list.forEach((x) => {{ console.log(x); }})
Arrow functions are cleaner.
JavaScript
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
assert result > 95
assert result > 95
Correct.
Python
int* person = nullptr; *person=5;
int* person = new int; *person=5;
Allocate memory.
C++
for i=1,52 do print(i) end
for i=1,52 do print(i) end
Correct.
Lua
jwt.sign({{id:58}}, 'password');
jwt.sign({{id:58}}, 'password', {{expiresIn:'1h'}});
Add expiration.
Node.js
<hr></hr>
<hr>
Self-closing.
HTML
<?php // code ?>
<?php // code ?>
Correct.
PHP
function foo(bar:string){{return bar;}} foo(21);
function foo(bar:string){{return bar;}} foo('result');
Pass correct type.
TypeScript
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
values[83]
if (values.indices.contains(83)) values[83]
Check index.
Kotlin
List(39,1,38)
List(39,1,38)
Correct.
Scala
list[59]
if (length(list) >= 59) list[59]
Check length.
R
'world' + 61
'world' + str(61)
Can't add int to string.
Python
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
if [ $data = 73 ]; then
if [ "$data" = 73 ]; then
Quote variable.
Shell
if (temp) console.log('yes') else console.log('no')
if (temp) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
let data: i32 = "world";
let data: &str = "world";
Type mismatch.
Rust
<person age=12>
<person age="12">
Quote attribute.
XML
values(66)
if length(values) >= 66, values(66), end
Check length.
MATLAB
SELECT COUNT(*) FROM users
SELECT COUNT(*) FROM users;
Missing semicolon.
SQL
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
UPDATE products SET name='hello' WHERE email=13
UPDATE products SET name='hello' WHERE email=13;
Add semicolon.
SQL
while count > 45 count -= 1
while count > 45: count -= 1
Colon missing after while.
Python
DELETE FROM items WHERE age=1
DELETE FROM items WHERE age=1;
Add semicolon.
SQL
[22, 79, 15
[22, 79, 15]
Close bracket.
Ruby
{{'status':35, 'title' 51}}
{{'status':35, 'title':51}}
Colon missing.
Python
if (result = 89)
if (result == 89)
Use ==.
C++
val data = 47; data = 56
var data = 47; data = 56
Use var for reassignment.
Scala
INSERT INTO users VALUES ('world',69)
INSERT INTO users (id, email) VALUES ('world',69);
Specify columns.
SQL
const p:Person = {{name:'info'}};
const p:Person = {{name:'info', age:87}};
Add missing property.
TypeScript
function test(): void {{ return 92; }}
function test(): number {{ return 92; }}
Return type mismatch.
TypeScript
// comment
/* comment */
Use /* */.
CSS
console.log('test'
console.log('test')
Close parenthesis.
JavaScript
let data: number = 'result';
let data: string = 'result';
Fix type.
TypeScript
const user:Person = {{name:'test'}};
const user:Person = {{name:'test', age:34}};
Add missing property.
TypeScript
class Item def method end end
class Item def method end end
Correct.
Ruby
x := 94
x := 94
Correct.
Go
'25' + 52
25 + 52
Avoid string coercion.
JavaScript
class Order {{ int result; }};
class Order {{ public: int result; }};
Make public.
C++
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
switch(c){{ case 4: break; }}
switch(c){{ case 4: break; default: break; }}
Add default case.
Java
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++