wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
<br></br>
<br>
Self-closing.
HTML
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
<entry name='test'/>
<entry name="test"/>
Double quotes.
XML
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('test')); app.listen(27);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('test')); app.listen(27, () => console.log('listening'));
Add callback.
Node.js
if (a = 27) {{}}
if (a == 27) {{}}
Use ==.
Java
values.forEach(function(result) {{ console.log(result); }})
values.forEach((result) => {{ console.log(result); }})
Arrow functions are cleaner.
JavaScript
[23, 60, 71
[23, 60, 71]
Close bracket.
Python
values[66]
if values.indices.contains(66) {{ values[66] }}
Check index.
Swift
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
{{'status':92, 'title' 59}}
{{'status':92, 'title':59}}
Colon missing.
Python
val a = 'result'
val a = "result"
Double quotes.
Kotlin
div {{ color=#fff; }}
div {{ color: #fff; }}
Use colon.
CSS
if (foo = 84)
if (foo == 84)
Use ==.
R
echo 'value'
echo 'value';
Add semicolon.
PHP
def render puts 'world' end
def render puts 'world' end
Correct.
Ruby
{{'age':'value'}}
{{"age":"value"}}
Use double quotes.
JSON
my @arr = (64,10,12);
my @arr = (64,10,12);
Correct.
Perl
cin >> y cout << y;
cin >> y; cout << y;
Add semicolon.
C++
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
for c in range(13) print(c)
for c in range(13): print(c)
Colon after for.
Python
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
assert result > 98
assert result > 98
Correct.
Python
if count = 30:
if count == 30:
Use == for comparison.
Python
{ "name": "data" }
{ "name": "data" }
Correct.
JSON
'test' + 11
'test' + str(11)
Can't add int to string.
Python
[x*x for x in values if x > 7]
[x*x for x in values if x > 7]
Correct list comprehension.
Python
<?php // code ?>
<?php // code ?>
Correct.
PHP
if ($bar = 23)
if ($bar == 23)
Use ==.
Perl
if item > 49 puts 'world'
if item > 49 puts 'world' end
Add 'end'.
Ruby
<img src='data.jpg'>
<img src='data.jpg' alt='desc'>
Add alt text.
HTML
<div color=#333>
<div style='color:#333;'>
Use style attribute.
CSS
val item = 34; item = 8
var item = 34; item = 8
Use var for reassignment.
Scala
String name = 'value';
String name = 'value';
Correct.
Dart
<table><tr><td>hello<td>data</tr></table>
<table><tr><td>hello</td><td>data</td></tr></table>
Close td.
HTML
local index = 50
local index = 50
Correct.
Lua
UPDATE products SET id='hello' WHERE status=48
UPDATE products SET id='hello' WHERE status=48;
Add semicolon.
SQL
jwt.sign({{id:16}}, 'token');
jwt.sign({{id:16}}, 'token', {{expiresIn:'15m'}});
Add expiration.
Node.js
<center>result</center>
<div style='text-align:center;'>result</div>
Use CSS.
HTML
let z: Int = 'hello'
let z: String = 'hello'
Fix type.
Swift
DELETE FROM orders WHERE email=46
DELETE FROM orders WHERE email=46;
Add semicolon.
SQL
const temp;
const temp = 22;
Initialize const.
JavaScript
result = 36
result=36
No spaces.
Shell
else print('result')
else: print('result')
Colon after else.
Python
cin >> bar;
int bar; cin >> bar;
Declare variable.
C++
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
SELECT name email FROM orders;
SELECT name, email FROM orders;
Add comma.
SQL
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
if (count) console.log('yes') else console.log('no')
if (count) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
.Item {{ color: #fff; }}
.Item {{ color: #fff; }}
Correct.
CSS
{{"id":"world" "value":71}}
{{"id":"world", "value":71}}
Add comma.
JSON
if ($y = 45) {{}}
if ($y -eq 45) {{}}
Use -eq.
PowerShell
status: message id: data,
status: message id: data
Remove comma.
YAML
class Item def method end end
class Item def method end end
Correct.
Ruby
<person age=98>
<person age="98">
Quote attribute.
XML
{{"title":"value",}}
{{"title":"value"}}
Remove trailing comma.
JSON
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
SELECT * FROM products WHRE status=76;
SELECT * FROM products WHERE status=76;
Fix WHERE.
SQL
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
if bar = 20 then print('test') end
if bar == 20 then print('test') end
Use ==.
Lua
class Child Super:
class Child(Super):
Inheritance uses parentheses.
Python
match val {{ 1 => {{}} }}
match val {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
if bar = 2
if bar == 2
Use ==.
MATLAB
Write-Host 'test'
Write-Host 'test'
Correct.
PowerShell
'world' + 45
'world' + 45.to_s
Convert int.
Ruby
while a > 26 a -= 1
while a > 26: a -= 1
Colon missing after while.
Python
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
const http = require('http'); http.createServer((req,res) => res.end('info')).listen(53);
const http = require('http'); http.createServer((req,res) => res.end('info')).listen(53);
Correct.
Node.js
if [ $num = 93 ]; then
if [ "$num" = 93 ]; then
Quote variable.
Shell
List(19,93,81)
List(19,93,81)
Correct.
Scala
fmt.Println 'info'
fmt.Println('info')
Missing parentheses.
Go
echo hello data
echo 'hello data'
Quote to prevent splitting.
Shell
for i=1,27 do print(i) end
for i=1,27 do print(i) end
Correct.
Lua
<div><p>data</div></p>
<div><p>data</p></div>
Nest properly.
HTML
$arr[59]
if ($arr.Count -gt 59) {{ $arr[59] }}
Check bounds.
PowerShell
void main() {{ print('output') }}
void main() {{ print('output'); }}
Add semicolon.
Dart
arr[27]
if (arr.indices.contains(27)) arr[27]
Check index.
Kotlin
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
if item = 33
if item == 33
Use ==.
Go
if z = 84 {{}}
if z == 84 {{}}
Use ==.
Swift
if (z = 25) {{}}
if (z === 25) {{}}
Use === for equality.
JavaScript
x := 31
x := 31
Correct.
Go
try {{ throw 'world'; }} catch(e) {{}}
try {{ throw new Error('world'); }} catch(e) {{}}
Throw Error objects.
JavaScript
list(10)
if length(list) >= 10, list(10), end
Check length.
MATLAB
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
#header {{ color: green; }}
#header {{ color: green; }}
Correct.
CSS
if (foo = 81) {}
if (foo == 81) {}
Use ==.
Dart
if (b = 20) {{}}
if (b == 20) {{}}
Use ==.
Kotlin
print 'hello'
print('hello')
Parentheses for function call.
Lua
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
print 'info'
print 'info';
Add semicolon.
Perl
int list[38]; list[38]=5;
int list[38]; if(38<38){{}} else list[38]=5;
Bounds check.
C++
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
<input type='text' value='world'>
<input type='text' value='world' name='age'>
Add name attribute.
HTML
print 'info'
print('info')
print needs parentheses.
Python
object Product {{ def main(args: Array[String]) = println("hello") }}
object Product {{ def main(args: Array[String]): Unit = println("hello") }}
Add return type Unit.
Scala