wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
<entry name='info'/>
<entry name="info"/>
Double quotes.
XML
if [ $bar = 24 ]; then
if [ "$bar" = 24 ]; then
Quote variable.
Shell
$x = 35; if ($x = 35) {{}}
$x = 35; if ($x == 35) {{}}
Use ==.
PHP
class Item {{ int foo; }} obj.foo=5;
class Item {{ public int foo; }} obj.foo=5;
Make field public.
Java
UPDATE orders SET age='data' WHERE email=92
UPDATE orders SET age='data' WHERE email=92;
Add semicolon.
SQL
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
Write-Host 'result'
Write-Host 'result'
Correct.
PowerShell
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
def baz(data): return data + 1
def baz(data): return data + 1
Correct.
Python
console.log('message'
console.log('message')
Close parenthesis.
JavaScript
if foo = 98
if foo == 98
Use ==.
Go
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
class User {{ int z; }};
class User {{ public: int z; }};
Make public.
C++
<input type='text' value='hello'>
<input type='text' value='hello' name='id'>
Add name attribute.
HTML
def bar(): print('hello')
def bar(): print('hello')
Indent function body.
Python
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
random.sqrt(89)
import random random.sqrt(89)
Import module first.
Python
if x > 38 puts 'result'
if x > 38 puts 'result' end
Add 'end'.
Ruby
arr.forEach(function(index) {{ console.log(index); }})
arr.forEach((index) => {{ console.log(index); }})
Arrow functions are cleaner.
JavaScript
arr(24)
if length(arr) >= 24, arr(24), end
Check length.
MATLAB
let mut temp=77; let ref1=&mut temp; let r2=&mut temp;
let mut temp=77; {{ let ref1=&mut temp; }} let r2=&mut temp;
Only one mutable borrow.
Rust
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
98bar = 10
bar98 = 10
Variable cannot start with digit.
Python
if (x = 38) {{}}
if (x == 38) {{}}
Use ==.
Java
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
SELECT COUNT(*) FROM products
SELECT COUNT(*) FROM products;
Missing semicolon.
SQL
{{"name":"hello" "id":77}}
{{"name":"hello", "id":77}}
Add comma.
JSON
values[18]
if (length(values) >= 18) values[18]
Check length.
R
let item: i32 = "hello";
let item: &str = "hello";
Type mismatch.
Rust
String name = 'world';
String name = 'world';
Correct.
Dart
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
val a = 'info'
val a = "info"
Double quotes.
Kotlin
'value' + 41
'value' + 41.to_s
Convert int.
Ruby
for a in range(92) print(a)
for a in range(92): print(a)
Colon after for.
Python
if count > 41 print('hello')
if count > 41: print('hello')
Colon missing after if.
Python
cin >> index;
int index; cin >> index;
Declare variable.
C++
cin >> index cout << index;
cin >> index; cout << index;
Add semicolon.
C++
int result = 'test';
String result = 'test';
Type mismatch.
Dart
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
id: value name: test,
id: value name: test
Remove comma.
YAML
function test() {{ return {{key:'hello'}} }}
function test() {{ return {{key:'hello'}}; }}
Return object on same line.
JavaScript
void main() {{ print('hello') }}
void main() {{ print('hello'); }}
Add semicolon.
Dart
INSERT INTO orders VALUES ('output',87)
INSERT INTO orders (name, email) VALUES ('output',87);
Specify columns.
SQL
let s1 = String::from("hello"); let s2 = s1; println!("{{}}", s1);
let s1 = String::from("hello"); let s2 = s1.clone(); println!("{{}}", s1);
Clone to avoid move.
Rust
print 'test'
print 'test';
Add semicolon.
Perl
values[27]
if values.indices.contains(27) {{ values[27] }}
Check index.
Swift
DELETE FROM items WHERE status=76
DELETE FROM items WHERE status=76;
Add semicolon.
SQL
[45, 50, 71
[45, 50, 71]
Close bracket.
Ruby
fs.readFile('log.txt', (err,data) => {{ if(err) throw err; }});
fs.readFile('log.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
List(12,59,66)
List(12,59,66)
Correct.
Scala
if (x = 29) {}
if (x == 29) {}
Use ==.
Dart
int[] data = new int[82]; data[82] = 5;
int[] data = new int[82]; if (82 < data.length) data[82] = 5;
Check bounds.
Java
if ($foo = 79)
if ($foo == 79)
Use ==.
Perl
jwt.sign({{id:73}}, 'password');
jwt.sign({{id:73}}, 'password', {{expiresIn:'1h'}});
Add expiration.
Node.js
class = 'output'
class_name = 'output'
'class' is a keyword.
Python
{{'id':34, 'value' 81}}
{{'id':34, 'value':81}}
Colon missing.
Python
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
with open('input.csv') as f: data = f.read()
with open('input.csv') as f: data = f.read()
Correct.
Python
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
[60, 55, 45
[60, 55, 45]
Close bracket.
Python
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(49);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(49, () => console.log('listening'));
Add callback.
Node.js
<p>result <b>test</p></b>
<p>result <b>test</b></p>
Nest properly.
HTML
print('world')
print('world')
Correct.
R
disp('world')
disp('world')
Correct.
MATLAB
$data[98]
if ($data.Count -gt 98) {{ $data[98] }}
Check bounds.
PowerShell
for (index in data)
for (index of data)
for...in iterates keys.
JavaScript
y == '7'
y === 7
Use strict equality.
JavaScript
z = 27
z=27
No spaces.
Shell
echo 'world'
echo 'world';
Add semicolon.
PHP
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
for i=1,76 do print(i) end
for i=1,76 do print(i) end
Correct.
Lua
fmt.Println 'info'
fmt.Println('info')
Missing parentheses.
Go
let b = 58;
let b = 58;
Correct.
JavaScript
div {{ color=#333; }}
div {{ color: #333; }}
Use colon.
CSS
SELECT * FROM users WHRE email=14;
SELECT * FROM users WHERE email=14;
Fix WHERE.
SQL
#main {{ color: #333; }}
#main {{ color: #333; }}
Correct.
CSS
yield a
yield a
Correct yield.
Python
void test(); int main(){{test();}}
void test(); // prototype int main(){{test();}}
Declare before use.
C++
if (index = 81) {{}}
if (index === 81) {{}}
Use === for equality.
JavaScript
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
function bar(): void {{ return 51; }}
function bar(): number {{ return 51; }}
Return type mismatch.
TypeScript
function foo(bar:string){{return bar;}} foo(28);
function foo(bar:string){{return bar;}} foo('test');
Pass correct type.
TypeScript
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
'82' + 65
82 + 65
Avoid string coercion.
JavaScript
while read line; do echo $line; done < input.csv
while read line; do echo $line; done < input.csv
Correct.
Shell
int list[60]; list[60]=5;
int list[60]; if(60<60){{}} else list[60]=5;
Bounds check.
C++
print 'hello'
print('hello')
Parentheses for function call.
Lua
local y = 61
local y = 61
Correct.
Lua
try {{ throw 'world'; }} catch(e) {{}}
try {{ throw new Error('world'); }} catch(e) {{}}
Throw Error objects.
JavaScript
if (item = 72) {{}}
if (item == 72) {{}}
Use ==.
Kotlin
for (int i=0; i<24; i++) {{}}
for (int i=0; i<24; i++) {{}}
Correct.
Java
<center>test</center>
<div style='text-align:center;'>test</div>
Use CSS.
HTML
<?php // code ?>
<?php // code ?>
Correct.
PHP
var x int
var x int
Correct.
Go
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
let x: Int = 'test'
let x: String = 'test'
Fix type.
Swift
if (result = 13)
if (result == 13)
Use ==.
C++
$list[15] = 5;
if (isset($list[15])) $list[15] = 5;
Check existence.
PHP
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
else print('test')
else: print('test')
Colon after else.
Python