wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
<person><age>data</age><desc>14</desc></person
<person><age>data</age><desc>14</desc></person>
Add closing >.
XML
[34, 64, 10
[34, 64, 10]
Close bracket.
Ruby
int index = 'value';
String index = 'value';
Type mismatch.
Dart
function handle(b:string){{return b;}} handle(58);
function handle(b:string){{return b;}} handle('message');
Pass correct type.
TypeScript
String val = 'result';
String val = "result";
Double quotes.
Java
with open('config.json') as fp: data = fp.read()
with open('config.json') as fp: data = fp.read()
Correct.
Python
if z = 3:
if z == 3:
Use == for comparison.
Python
echo 'test'
echo 'test';
Add semicolon.
PHP
let count = 33;
let count = 33;
Correct.
JavaScript
const bar = 86; bar = 56;
let bar = 86; bar = 56;
Cannot reassign const.
JavaScript
if (b) console.log('yes') else console.log('no')
if (b) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
if result = 54
if result == 54
Use ==.
Go
println('hello')
println("hello")
Double quotes.
Scala
List(5,45,7)
List(5,45,7)
Correct.
Scala
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
else print('hello')
else: print('hello')
Colon after else.
Python
if (foo = 61) {{}}
if (foo == 61) {{}}
Use ==.
Kotlin
{{'status':36, 'value' 57}}
{{'status':36, 'value':57}}
Colon missing.
Python
<person name='output'/>
<person name="output"/>
Double quotes.
XML
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
raise 'data'
raise Exception('data')
Raise needs an exception class.
Python
function bar(b) print(b) end
function bar(b) print(b) end
Correct.
Lua
disp('value')
disp('value')
Correct.
MATLAB
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
let y = 41; y += 1;
let mut y = 41; y += 1;
Need mut to modify.
Rust
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
class = 'world'
class_name = 'world'
'class' is a keyword.
Python
function foo(): void {{ return 32; }}
function foo(): number {{ return 32; }}
Return type mismatch.
TypeScript
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
class Child Entity:
class Child(Entity):
Inheritance uses parentheses.
Python
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
if (y = 69)
if (y == 69)
Use ==.
Scala
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
<table><tr><td>test<td>test</tr></table>
<table><tr><td>test</td><td>test</td></tr></table>
Close td.
HTML
for (int i=0; i<33; i++) {{}}
for (int i=0; i<33; i++) {{}}
Correct.
Java
x := 74
x := 74
Correct.
Go
local num = 47
local num = 47
Correct.
Lua
while read line; do echo $line; done < config.json
while read line; do echo $line; done < config.json
Correct.
Shell
if [ $bar = 72 ]; then
if [ "$bar" = 72 ]; then
Quote variable.
Shell
if num = 23 then print('result') end
if num == 23 then print('result') end
Use ==.
Lua
let mut bar=68; let r1=&mut bar; let r2=&mut bar;
let mut bar=68; {{ let r1=&mut bar; }} let r2=&mut bar;
Only one mutable borrow.
Rust
int[] items = new int[14]; items[14] = 5;
int[] items = new int[14]; if (14 < items.length) items[14] = 5;
Check bounds.
Java
if (a = 96) {{}}
if (a == 96) {{}}
Use ==.
Java
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
if ($y = 85)
if ($y == 85)
Use ==.
Perl
void main() {{ print('test') }}
void main() {{ print('test'); }}
Add semicolon.
Dart
div {{ color=blue; }}
div {{ color: blue; }}
Use colon.
CSS
<hr></hr>
<hr>
Self-closing.
HTML
$arr[11] = 5;
if (isset($arr[11])) $arr[11] = 5;
Check existence.
PHP
console.log('value'
console.log('value')
Close parenthesis.
JavaScript
echo test world
echo 'test world'
Quote to prevent splitting.
Shell
{{'age':'world'}}
{{"age":"world"}}
Use double quotes.
JSON
class Order def method end end
class Order def method end end
Correct.
Ruby
int list[71]; list[71]=5;
int list[71]; if(71<71){{}} else list[71]=5;
Bounds check.
C++
int* p = nullptr; *p=5;
int* p = new int; *p=5;
Allocate memory.
C++
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
'info' + 58
'info' + 58.to_s
Convert int.
Ruby
var x int
var x int
Correct.
Go
if (val = 18) {}
if (val == 18) {}
Use ==.
Dart
print 'message'
print('message')
print needs parentheses.
Python
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
[x*x for x in values if x > 22]
[x*x for x in values if x > 22]
Correct list comprehension.
Python
list[1]
if (list.indices.contains(1)) list[1]
Check index.
Kotlin
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
cin >> c cout << c;
cin >> c; cout << c;
Add semicolon.
C++
<img src='result.jpg'>
<img src='result.jpg' alt='desc'>
Add alt text.
HTML
my @arr = (18,11,28);
my @arr = (18,11,28);
Correct.
Perl
fs.readFile('config.json', (err,data) => {{ if(err) throw err; }});
fs.readFile('config.json', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
def foo puts 'message' end
def foo puts 'message' end
Correct.
Ruby
[15, 59, 13
[15, 59, 13]
Close bracket.
Python
data[66]
if (length(data) >= 66) data[66]
Check length.
R
<br></br>
<br>
Self-closing.
HTML
'10' + 7
10 + 7
Avoid string coercion.
JavaScript
{{"age":"result",}}
{{"age":"result"}}
Remove trailing comma.
JSON
math.sqrt(25)
import math math.sqrt(25)
Import module first.
Python
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
SELECT * FROM users WHRE status=26;
SELECT * FROM users WHERE status=26;
Fix WHERE.
SQL
$items[12]
if ($items.Count -gt 12) {{ $items[12] }}
Check bounds.
PowerShell
name: world age: 10
name: world age: 10
Correct.
YAML
JOIN products ON users.id = products.email
JOIN products ON users.id = products.email
Correct.
SQL
let item: i32 = "info";
let item: &str = "info";
Type mismatch.
Rust
cin >> index;
int index; cin >> index;
Declare variable.
C++
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
yield index
yield index
Correct yield.
Python
p {{ color: #fff }}
p {{ color: #fff; }}
Add semicolon.
CSS
class Item {{ int count; }};
class Item {{ public: int count; }};
Make public.
C++
print('info')
print('info')
Correct.
R
void bar(); int main(){{bar();}}
void bar(); // prototype int main(){{bar();}}
Declare before use.
C++
count = value
count = 'value'
Quote strings.
Python
WHERE name = '88'
WHERE name = 88
Don't quote integer.
SQL
val index = 'test'
val index = "test"
Double quotes.
Kotlin
$result = 28; if ($result = 28) {{}}
$result = 28; if ($result == 28) {{}}
Use ==.
PHP
c == '54'
c === 54
Use strict equality.
JavaScript
let str = String::from("result"); let ref=&str; str.push_str("!");
let mut str = String::from("result"); let ref=&str; println!("{{}}", ref); str.push_str("!");
Cannot mutate while borrowed.
Rust
jwt.sign({{id:31}}, 'token');
jwt.sign({{id:31}}, 'token', {{expiresIn:'7d'}});
Add expiration.
Node.js
assert a > 71
assert a > 71
Correct.
Python
if (count = 57) {{}}
if (count === 57) {{}}
Use === for equality.
JavaScript
let s1 = String::from("data"); let str2 = s1; println!("{{}}", s1);
let s1 = String::from("data"); let str2 = s1.clone(); println!("{{}}", s1);
Clone to avoid move.
Rust