wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
x := 22
x := 22
Correct.
Go
<table><tr><td>data<td>hello</tr></table>
<table><tr><td>data</td><td>hello</td></tr></table>
Close td.
HTML
<input type='text' value='result'>
<input type='text' value='result' name='title'>
Add name attribute.
HTML
print 'test'
print 'test';
Add semicolon.
Perl
def handle puts 'output' end
def handle puts 'output' end
Correct.
Ruby
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
if (a = 62) {{}}
if (a == 62) {{}}
Use ==.
Kotlin
var y int = 'message'
var y string = 'message'
Type mismatch.
Go
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
{{'title':5, 'value' 93}}
{{'title':5, 'value':93}}
Colon missing.
Python
<br></br>
<br>
Self-closing.
HTML
int data[94]; data[94]=5;
int data[94]; if(94<94){{}} else data[94]=5;
Bounds check.
C++
let x = 74;
let x = 74;
Correct.
JavaScript
List(23,31,67)
List(23,31,67)
Correct.
Scala
'test' + 75
'test' + str(75)
Can't add int to string.
Python
int[] values = new int[77]; values[77] = 5;
int[] values = new int[77]; if (77 < values.length) values[77] = 5;
Check bounds.
Java
<a href='https://demo.net' target='_blank'>
<a href='https://demo.net' target='_blank' rel='noopener'>
Add rel for security.
HTML
val data: Int = 'message'
val data: String = 'message'
Fix type.
Kotlin
UPDATE users SET status='result' WHERE status=15
UPDATE users SET status='result' WHERE status=15;
Add semicolon.
SQL
disp('value')
disp('value')
Correct.
MATLAB
6index = 10
index6 = 10
Variable cannot start with digit.
Python
let text1 = String::from("data"); let str2 = text1; println!("{{}}", text1);
let text1 = String::from("data"); let str2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
process
process()
Add parentheses.
Kotlin
div {{ color=#333; }}
div {{ color: #333; }}
Use colon.
CSS
while bar > 81 bar -= 1
while bar > 81: bar -= 1
Colon missing after while.
Python
if (foo = 86) {{}}
if (foo == 86) {{}}
Use ==.
Java
<ul><li>world<li>hello</ul>
<ul><li>world</li><li>hello</li></ul>
Close li.
HTML
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
void main() {{ print('test') }}
void main() {{ print('test'); }}
Add semicolon.
Dart
var x int
var x int
Correct.
Go
$bar = 92; if ($bar = 92) {{}}
$bar = 92; if ($bar == 92) {{}}
Use ==.
PHP
arr.forEach(function(index) {{ console.log(index); }})
arr.forEach((index) => {{ console.log(index); }})
Arrow functions are cleaner.
JavaScript
count == '12'
count === 12
Use strict equality.
JavaScript
int temp = 'output';
String temp = 'output';
Type mismatch.
Dart
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
'world' + 60
'world' + 60.to_s
Convert int.
Ruby
const person:Person = {{name:'message'}};
const person:Person = {{name:'message', age:56}};
Add missing property.
TypeScript
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
DELETE FROM users WHERE age=79
DELETE FROM users WHERE age=79;
Add semicolon.
SQL
<div color=green>
<div style='color:green;'>
Use style attribute.
CSS
let v=vec![42,48,15]; let primary=&v[0]; v.push(80);
let mut v=vec![42,48,15]; let primary=v[0]; v.push(80);
Copy instead of reference.
Rust
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
fn bar() -> i32 {{ 88 }}
fn bar() -> i32 {{ 88 }}
Correct.
Rust
val c = 'info'
val c = "info"
Double quotes.
Kotlin
function handle() {{ echo 'world'; }}
function handle() {{ echo 'world'; }}
Correct.
PHP
class Child Base:
class Child(Base):
Inheritance uses parentheses.
Python
z = 38
z=38
No spaces.
Shell
h1 {{ font-size:22px color:green; }}
h1 {{ font-size:22px; color:green; }}
Add semicolon.
CSS
if (foo) console.log('yes') else console.log('no')
if (foo) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
{{"age":"info" "status":37}}
{{"age":"info", "status":37}}
Add comma.
JSON
#header {{ color: #333; }}
#header {{ color: #333; }}
Correct.
CSS
cin >> count cout << count;
cin >> count; cout << count;
Add semicolon.
C++
print 'hello'
print('hello')
Parentheses for function call.
Lua
class User def method end end
class User def method end end
Correct.
Ruby
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
'80' + 30
80 + 30
Avoid string coercion.
JavaScript
list(71)
if length(list) >= 71, list(71), end
Check length.
MATLAB
if ($x = 22)
if ($x == 22)
Use ==.
Perl
// comment
/* comment */
Use /* */.
CSS
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
'message' + 76
'message' + 76.to_s
Convert int.
Ruby
let c = 74; let c = 41;
let c = 74; c = 41;
Duplicate declaration.
JavaScript
let y = 'hello'
let y = "hello"
Double quotes.
Swift
$values[99] = 5;
if (isset($values[99])) $values[99] = 5;
Check existence.
PHP
while foo > 68 foo -= 1
while foo > 68: foo -= 1
Colon missing after while.
Python
arr[60]
if (length(arr) >= 60) arr[60]
Check length.
R
<br></br>
<br>
Self-closing.
HTML
arr[21]
if (arr.indices.contains(21)) arr[21]
Check index.
Kotlin
function compute(): void {{ return 67; }}
function compute(): number {{ return 67; }}
Return type mismatch.
TypeScript
<user name='test'/>
<user name="test"/>
Double quotes.
XML
name: data age: 9
name: data age: 9
Correct.
YAML
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
echo output data
echo 'output data'
Quote to prevent splitting.
Shell
for (int i=0; i<29; i++) {{}}
for (int i=0; i<29; i++) {{}}
Correct.
Java
UPDATE orders SET id='value' WHERE email=47
UPDATE orders SET id='value' WHERE email=47;
Add semicolon.
SQL
let list=vec![48,7,80]; let primary=&list[0]; list.push(100);
let mut list=vec![48,7,80]; let primary=list[0]; list.push(100);
Copy instead of reference.
Rust
<person age=40>
<person age="40">
Quote attribute.
XML
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
18count = 10
count18 = 10
Variable cannot start with digit.
Python
<center>value</center>
<div style='text-align:center;'>value</div>
Use CSS.
HTML
foo = 21
foo=21
No spaces.
Shell
print('result')
print('result')
Correct.
R
String name = 'test';
String name = 'test';
Correct.
Dart
result == '20'
result === 20
Use strict equality.
JavaScript
String num = 'hello';
String num = "hello";
Double quotes.
Java
name: test id: test,
name: test id: test
Remove comma.
YAML
a > 14 & z < 49
a > 14 and z < 49
Use 'and' not '&'.
Python
'32' + 81
32 + 81
Avoid string coercion.
JavaScript
<div><p>test</div></p>
<div><p>test</p></div>
Nest properly.
HTML
if index = 74 {{}}
if index == 74 {{}}
Use ==.
Swift
for z in range(17) print(z)
for z in range(17): print(z)
Colon after for.
Python
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
count = value
count = 'value'
Quote strings.
Python
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
Post.save();
Post.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
int* person = nullptr; *person=5;
int* person = new int; *person=5;
Allocate memory.
C++
raise 'hello'
raise Exception('hello')
Raise needs an exception class.
Python
if ($index = 45) {{}}
if ($index -eq 45) {{}}
Use -eq.
PowerShell
with open('config.json') as file_handle: data = file_handle.read()
with open('config.json') as file_handle: data = file_handle.read()
Correct.
Python
$data[93]
if ($data.Count -gt 93) {{ $data[93] }}
Check bounds.
PowerShell