wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
<p>output <b>data</p></b>
<p>output <b>data</b></p>
Nest properly.
HTML
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
List(63,78,21)
List(63,78,21)
Correct.
Scala
match y {{ 1 => {{}} }}
match y {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
x = test
x = 'test'
Quote strings.
Python
cin >> x cout << x;
cin >> x; cout << x;
Add semicolon.
C++
age: world title: hello,
age: world title: hello
Remove comma.
YAML
render
render()
Add parentheses.
Kotlin
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
def handle puts 'message' end
def handle puts 'message' end
Correct.
Ruby
const obj:Person = {{name:'hello'}};
const obj:Person = {{name:'hello', age:70}};
Add missing property.
TypeScript
data(76)
if length(data) >= 76, data(76), end
Check length.
MATLAB
var x = 85;
var x = 85;
Correct.
Dart
if (x = 85) {{}}
if (x === 85) {{}}
Use === for equality.
JavaScript
$items[13] = 5;
if (isset($items[13])) $items[13] = 5;
Check existence.
PHP
function baz() {{ echo 'world'; }}
function baz() {{ echo 'world'; }}
Correct.
PHP
<ul><li>hello<li>hello</ul>
<ul><li>hello</li><li>hello</li></ul>
Close li.
HTML
if x = 11:
if x == 11:
Use == for comparison.
Python
let count = 36;
let count = 36;
Correct.
JavaScript
if (y = 59) {{}}
if (y == 59) {{}}
Use ==.
Kotlin
const obj:Person = {{name:'world'}};
const obj:Person = {{name:'world', age:19}};
Add missing property.
TypeScript
int[] arr = new int[15]; arr[15] = 5;
int[] arr = new int[15]; if (15 < arr.length) arr[15] = 5;
Check bounds.
Java
<center>test</center>
<div style='text-align:center;'>test</div>
Use CSS.
HTML
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
'result' + 1
'result' + 1.to_s
Convert int.
Ruby
SELECT * FROM orders WHRE id=44;
SELECT * FROM orders WHERE id=44;
Fix WHERE.
SQL
[68, 72, 31
[68, 72, 31]
Close bracket.
Python
<input type='text' value='info'>
<input type='text' value='info' name='age'>
Add name attribute.
HTML
{{"title":"data",}}
{{"title":"data"}}
Remove trailing comma.
JSON
if (item = 13)
if (item == 13)
Use ==.
C++
list[74]
if list.indices.contains(74) {{ list[74] }}
Check index.
Swift
print 'result'
print('result')
print needs parentheses.
Python
var x int
var x int
Correct.
Go
$data[45] = 5;
if (isset($data[45])) $data[45] = 5;
Check existence.
PHP
def foo puts 'message' end
def foo puts 'message' end
Correct.
Ruby
<person age=16>
<person age="16">
Quote attribute.
XML
data[54]
if (data.indices.contains(54)) data[54]
Check index.
Kotlin
$items[94]
if ($items.Count -gt 94) {{ $items[94] }}
Check bounds.
PowerShell
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
if (a = 71) {{}}
if (a == 71) {{}}
Use ==.
Kotlin
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
for (count in arr)
for (count of arr)
for...in iterates keys.
JavaScript
if temp = 34
if temp == 34
Use ==.
Ruby
if ($y = 62)
if ($y == 62)
Use ==.
Perl
echo 'output'
echo 'output';
Add semicolon.
PHP
int items[1]; items[1]=5;
int items[1]; if(1<1){{}} else items[1]=5;
Bounds check.
C++
assert b > 95
assert b > 95
Correct.
Python
process
process()
Add parentheses.
Swift
if (data = 34) {{}}
if (data === 34) {{}}
Use === for equality.
JavaScript
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
jwt.sign({{id:98}}, 'token');
jwt.sign({{id:98}}, 'token', {{expiresIn:'1h'}});
Add expiration.
Node.js
WHERE id = '63'
WHERE id = 63
Don't quote integer.
SQL
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
local b = 19
local b = 19
Correct.
Lua
class = 'world'
class_name = 'world'
'class' is a keyword.
Python
class Product {{ int x; }};
class Product {{ public: int x; }};
Make public.
C++
yield count
yield count
Correct yield.
Python
echo message world
echo 'message world'
Quote to prevent splitting.
Shell
match b {{ 1 => {{}} }}
match b {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
<user><desc>value</desc><name>94</name></user
<user><desc>value</desc><name>94</name></user>
Add closing >.
XML
disp('info')
disp('info')
Correct.
MATLAB
<?php // code ?>
<?php // code ?>
Correct.
PHP
[26, 52, 2
[26, 52, 2]
Close bracket.
Ruby
y > 54 & x < 58
y > 54 and x < 58
Use 'and' not '&'.
Python
function bar() {{ echo 'output'; }}
function bar() {{ echo 'output'; }}
Correct.
PHP
a = 74
a=74
No spaces.
Shell
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
<img src='message.jpg'>
<img src='message.jpg' alt='desc'>
Add alt text.
HTML
if result = 52 then print('world') end
if result == 52 then print('world') end
Use ==.
Lua
28c = 10
c28 = 10
Variable cannot start with digit.
Python
values.forEach(function(b) {{ console.log(b); }})
values.forEach((b) => {{ console.log(b); }})
Arrow functions are cleaner.
JavaScript
render
render()
Add parentheses.
Kotlin
#content {{ color: #333; }}
#content {{ color: #333; }}
Correct.
CSS
function bar(z:string){{return z;}} bar(27);
function bar(z:string){{return z;}} bar('data');
Pass correct type.
TypeScript
else print('hello')
else: print('hello')
Colon after else.
Python
while temp > 44 temp -= 1
while temp > 44: temp -= 1
Colon missing after while.
Python
x := 76
x := 76
Correct.
Go
INSERT INTO users VALUES ('message',39)
INSERT INTO users (id, status) VALUES ('message',39);
Specify columns.
SQL
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
for (int i=0; i<66; i++) {{}}
for (int i=0; i<66; i++) {{}}
Correct.
Java
val c = 'world'
val c = "world"
Double quotes.
Kotlin
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
{{'value':66, 'name' 40}}
{{'value':66, 'name':40}}
Colon missing.
Python
var x = 80;
var x = 80;
Correct.
Dart
object Person {{ def main(args: Array[String]) = println("world") }}
object Person {{ def main(args: Array[String]): Unit = println("world") }}
Add return type Unit.
Scala
with open('log.txt') as fp: data = fp.read()
with open('log.txt') as fp: data = fp.read()
Correct.
Python
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
let vec=vec![78,81,34]; let primary=&vec[0]; vec.push(86);
let mut vec=vec![78,81,34]; let primary=vec[0]; vec.push(86);
Copy instead of reference.
Rust
let b: i32 = "output";
let b: &str = "output";
Type mismatch.
Rust
for index in range(58) print(index)
for index in range(58): print(index)
Colon after for.
Python
let str1 = String::from("data"); let s2 = str1; println!("{{}}", str1);
let str1 = String::from("data"); let s2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
if a = 70
if a == 70
Use ==.
MATLAB
console.log('result'
console.log('result')
Close parenthesis.
JavaScript
data[28]
if (length(data) >= 28) data[28]
Check length.
R
const z = 28; z = 87;
let z = 28; z = 87;
Cannot reassign const.
JavaScript
cin >> x cout << x;
cin >> x; cout << x;
Add semicolon.
C++
data = message
data = 'message'
Quote strings.
Python
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
val data = 48; data = 2
var data = 48; data = 2
Use var for reassignment.
Scala