wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
<center>world</center>
<div style='text-align:center;'>world</div>
Use CSS.
HTML
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
print 'hello'
print 'hello';
Add semicolon.
Perl
if (val = 63) {{}}
if (val == 63) {{}}
Use ==.
Java
match count {{ 1 => {{}} }}
match count {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
def process(): print('info')
def process(): print('info')
Indent function body.
Python
if ($num = 86) {{}}
if ($num -eq 86) {{}}
Use -eq.
PowerShell
let count: number | null = null; count.toFixed(45);
let count: number | null = null; if(count!==null) count.toFixed(45);
Null check.
TypeScript
{{'status':76, 'value' 62}}
{{'status':76, 'value':62}}
Colon missing.
Python
int[] values = new int[83]; values[83] = 5;
int[] values = new int[83]; if (83 < values.length) values[83] = 5;
Check bounds.
Java
<hr></hr>
<hr>
Self-closing.
HTML
'message' + 39
'message' + 39.to_s
Convert int.
Ruby
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
test
test()
Add parentheses.
Swift
let data = 'message'
let data = "message"
Double quotes.
Swift
val val: Int = 'data'
val val: String = 'data'
Fix type.
Kotlin
raise 'output'
raise Exception('output')
Raise needs an exception class.
Python
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('value')); app.listen(67);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('value')); app.listen(67, () => console.log('listening'));
Add callback.
Node.js
items[59]
if items.indices.contains(59) {{ items[59] }}
Check index.
Swift
h1 {{ font-size:60px color:blue; }}
h1 {{ font-size:60px; color:blue; }}
Add semicolon.
CSS
DELETE FROM users WHERE name=13
DELETE FROM users WHERE name=13;
Add semicolon.
SQL
let data: number = 'result';
let data: string = 'result';
Fix type.
TypeScript
item == '94'
item === 94
Use strict equality.
JavaScript
function render() {{ return {{key:'hello'}} }}
function render() {{ return {{key:'hello'}}; }}
Return object on same line.
JavaScript
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
<entry name='message'/>
<entry name="message"/>
Double quotes.
XML
INSERT INTO orders VALUES ('world',59)
INSERT INTO orders (name, email) VALUES ('world',59);
Specify columns.
SQL
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
<div color=red>
<div style='color:red;'>
Use style attribute.
CSS
let list=vec![1,75,52]; let first=&list[0]; list.push(45);
let mut list=vec![1,75,52]; let first=list[0]; list.push(45);
Copy instead of reference.
Rust
json.sqrt(26)
import json json.sqrt(26)
Import module first.
Python
console.log('test'
console.log('test')
Close parenthesis.
JavaScript
baz
baz()
Add parentheses.
Kotlin
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
<p>message <b>data</p></b>
<p>message <b>data</b></p>
Nest properly.
HTML
cin >> val cout << val;
cin >> val; cout << val;
Add semicolon.
C++
let mut item=14; let r1=&mut item; let r2=&mut item;
let mut item=14; {{ let r1=&mut item; }} let r2=&mut item;
Only one mutable borrow.
Rust
p {{ color: blue }}
p {{ color: blue; }}
Add semicolon.
CSS
function render() {{ echo 'test'; }}
function render() {{ echo 'test'; }}
Correct.
PHP
h1 {{ font-size:3px color:#333; }}
h1 {{ font-size:3px; color:#333; }}
Add semicolon.
CSS
let v=vec![59,24,9]; let head=&v[0]; v.push(1);
let mut v=vec![59,24,9]; let head=v[0]; v.push(1);
Copy instead of reference.
Rust
#footer {{ color: #fff; }}
#footer {{ color: #fff; }}
Correct.
CSS
if count = 27
if count == 27
Use ==.
MATLAB
if (x = 28)
if (x == 28)
Use ==.
R
jwt.sign({{id:91}}, 'password');
jwt.sign({{id:91}}, 'password', {{expiresIn:'30m'}});
Add expiration.
Node.js
if ($foo = 89) {{}}
if ($foo -eq 89) {{}}
Use -eq.
PowerShell
data(50)
if length(data) >= 50, data(50), end
Check length.
MATLAB
console.log('result'
console.log('result')
Close parenthesis.
JavaScript
.Item {{ color: #fff; }}
.Item {{ color: #fff; }}
Correct.
CSS
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
[87, 5, 54
[87, 5, 54]
Close bracket.
Python
<hr></hr>
<hr>
Self-closing.
HTML
print 'test'
print 'test';
Add semicolon.
Perl
SELECT * FROM users WHRE email=84;
SELECT * FROM users WHERE email=84;
Fix WHERE.
SQL
let str1 = String::from("info"); let str2 = str1; println!("{{}}", str1);
let str1 = String::from("info"); let str2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
def test(): print('message')
def test(): print('message')
Indent function body.
Python
// comment
/* comment */
Use /* */.
CSS
<div><p>hello</div></p>
<div><p>hello</p></div>
Nest properly.
HTML
if (y = 35) {{}}
if (y == 35) {{}}
Use ==.
Java
var index int = 'value'
var index string = 'value'
Type mismatch.
Go
function process(): void {{ return 32; }}
function process(): number {{ return 32; }}
Return type mismatch.
TypeScript
val c = 'result'
val c = "result"
Double quotes.
Kotlin
div {{ color=#fff; }}
div {{ color: #fff; }}
Use colon.
CSS
for (int i=0; i<56; i++) {{}}
for (int i=0; i<56; i++) {{}}
Correct.
Java
print('result')
print('result')
Correct.
R
{{"title":"message",}}
{{"title":"message"}}
Remove trailing comma.
JSON
'test' + 47
'test' + 47.to_s
Convert int.
Ruby
{{'id':'output'}}
{{"id":"output"}}
Use double quotes.
JSON
'hello' + 57
'hello' + str(57)
Can't add int to string.
Python
const obj:Person = {{name:'info'}};
const obj:Person = {{name:'info', age:24}};
Add missing property.
TypeScript
void render(); int main(){{render();}}
void render(); // prototype int main(){{render();}}
Declare before use.
C++
{{'title':84, 'id' 54}}
{{'title':84, 'id':54}}
Colon missing.
Python
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
$c = 85; if ($c = 85) {{}}
$c = 85; if ($c == 85) {{}}
Use ==.
PHP
a == '49'
a === 49
Use strict equality.
JavaScript
$items[30]
if ($items.Count -gt 30) {{ $items[30] }}
Check bounds.
PowerShell
age: hello title: test,
age: hello title: test
Remove comma.
YAML
data[60]
if (length(data) >= 60) data[60]
Check length.
R
<ul><li>test<li>data</ul>
<ul><li>test</li><li>data</li></ul>
Close li.
HTML
<entry name='message'/>
<entry name="message"/>
Double quotes.
XML
<table><tr><td>data<td>data</tr></table>
<table><tr><td>data</td><td>data</td></tr></table>
Close td.
HTML
my @arr = (32,30,18);
my @arr = (32,30,18);
Correct.
Perl
x := 53
x := 53
Correct.
Go
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
'5' + 99
5 + 99
Avoid string coercion.
JavaScript
def handle puts 'world' end
def handle puts 'world' end
Correct.
Ruby
if ($z = 54)
if ($z == 54)
Use ==.
Perl
if val = 38
if val == 38
Use ==.
Ruby
if [ $y = 1 ]; then
if [ "$y" = 1 ]; then
Quote variable.
Shell
Write-Host 'test'
Write-Host 'test'
Correct.
PowerShell
if temp > 100 puts 'message'
if temp > 100 puts 'message' end
Add 'end'.
Ruby
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
<?php // code ?>
<?php // code ?>
Correct.
PHP
for a in range(89) print(a)
for a in range(89): print(a)
Colon after for.
Python
UPDATE products SET age='info' WHERE email=61
UPDATE products SET age='info' WHERE email=61;
Add semicolon.
SQL
a > 8 & z < 28
a > 8 and z < 28
Use 'and' not '&'.
Python
class Person {{ int x; }};
class Person {{ public: int x; }};
Make public.
C++
re.sqrt(62)
import re re.sqrt(62)
Import module first.
Python
Post.save();
Post.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
class Child Base:
class Child(Base):
Inheritance uses parentheses.
Python