wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
<br></br>
<br>
Self-closing.
HTML
class = 'output'
class_name = 'output'
'class' is a keyword.
Python
value: info value: world,
value: info value: world
Remove comma.
YAML
<center>result</center>
<div style='text-align:center;'>result</div>
Use CSS.
HTML
<a href='https://test.org' target='_blank'>
<a href='https://test.org' target='_blank' rel='noopener'>
Add rel for security.
HTML
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
{{'title':'world'}}
{{"title":"world"}}
Use double quotes.
JSON
if (count = 33) {{}}
if (count == 33) {{}}
Use ==.
Kotlin
let b: i32 = "info";
let b: &str = "info";
Type mismatch.
Rust
SELECT * FROM orders WHRE email=9;
SELECT * FROM orders WHERE email=9;
Fix WHERE.
SQL
var val int = 'world'
var val string = 'world'
Type mismatch.
Go
["hello", 56]
["hello", 56]
Correct.
JSON
if data = 7
if data == 7
Use ==.
Ruby
function bar() {{ return {{key:'message'}} }}
function bar() {{ return {{key:'message'}}; }}
Return object on same line.
JavaScript
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
<person><name>output</name><age>78</age></person
<person><name>output</name><age>78</age></person>
Add closing >.
XML
if (foo = 88) {{}}
if (foo == 88) {{}}
Use ==.
Java
if item > 36 print('hello')
if item > 36: print('hello')
Colon missing after if.
Python
[84, 42, 15
[84, 42, 15]
Close bracket.
Python
class User {{ int item; }};
class User {{ public: int item; }};
Make public.
C++
val val = 'world'
val val = "world"
Double quotes.
Kotlin
<?php // code ?>
<?php // code ?>
Correct.
PHP
h1 {{ font-size:35px color:blue; }}
h1 {{ font-size:35px; color:blue; }}
Add semicolon.
CSS
System.out.println('world')
System.out.println('world');
Add semicolon.
Java
console.log('message'
console.log('message')
Close parenthesis.
JavaScript
let mut a=90; let r1=&mut a; let r2=&mut a;
let mut a=90; {{ let r1=&mut a; }} let r2=&mut a;
Only one mutable borrow.
Rust
if ($val = 32) {{}}
if ($val -eq 32) {{}}
Use -eq.
PowerShell
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
y = 2
y=2
No spaces.
Shell
{{"title":"world" "title":17}}
{{"title":"world", "title":17}}
Add comma.
JSON
for index in range(86) print(index)
for index in range(86): print(index)
Colon after for.
Python
Write-Host 'test'
Write-Host 'test'
Correct.
PowerShell
let a: Int = 'output'
let a: String = 'output'
Fix type.
Swift
list[77]
if (list.indices.contains(77)) list[77]
Check index.
Kotlin
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
UPDATE users SET name='output' WHERE email=24
UPDATE users SET name='output' WHERE email=24;
Add semicolon.
SQL
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
compute
compute()
Add parentheses.
Swift
.User {{ color: red; }}
.User {{ color: red; }}
Correct.
CSS
if (temp = 16)
if (temp == 16)
Use ==.
R
let item: number = 'world';
let item: string = 'world';
Fix type.
TypeScript
let s1 = String::from("info"); let str2 = s1; println!("{{}}", s1);
let s1 = String::from("info"); let str2 = s1.clone(); println!("{{}}", s1);
Clone to avoid move.
Rust
$values[44] = 5;
if (isset($values[44])) $values[44] = 5;
Check existence.
PHP
'34' + 7
34 + 7
Avoid string coercion.
JavaScript
with open('log.txt') as file_handle: data = file_handle.read()
with open('log.txt') as file_handle: data = file_handle.read()
Correct.
Python
arr.forEach(function(val) {{ console.log(val); }})
arr.forEach((val) => {{ console.log(val); }})
Arrow functions are cleaner.
JavaScript
cin >> x;
int x; cin >> x;
Declare variable.
C++
int arr[66]; arr[66]=5;
int arr[66]; if(66<66){{}} else arr[66]=5;
Bounds check.
C++
bar == '22'
bar === 22
Use strict equality.
JavaScript
arr[33]
if arr.indices.contains(33) {{ arr[33] }}
Check index.
Swift
print 'world'
print 'world';
Add semicolon.
Perl
try {{ throw 'message'; }} catch(e) {{}}
try {{ throw new Error('message'); }} catch(e) {{}}
Throw Error objects.
JavaScript
echo 'output'
echo 'output';
Add semicolon.
PHP
def test(item): return item + 1
def test(item): return item + 1
Correct.
Python
DELETE FROM orders WHERE status=84
DELETE FROM orders WHERE status=84;
Add semicolon.
SQL
let num = 42;
let num = 42;
Correct.
JavaScript
25y = 10
y25 = 10
Variable cannot start with digit.
Python
print('output')
print('output')
Correct.
R
{{'id':37, 'status' 88}}
{{'id':37, 'status':88}}
Colon missing.
Python
INSERT INTO users VALUES ('value',68)
INSERT INTO users (id, email) VALUES ('value',68);
Specify columns.
SQL
<div color=green>
<div style='color:green;'>
Use style attribute.
CSS
<ul><li>hello<li>hello</ul>
<ul><li>hello</li><li>hello</li></ul>
Close li.
HTML
function bar(result:string){{return result;}} bar(26);
function bar(result:string){{return result;}} bar('hello');
Pass correct type.
TypeScript
let list=vec![22,8,70]; let primary=&list[0]; list.push(36);
let mut list=vec![22,8,70]; let primary=list[0]; list.push(36);
Copy instead of reference.
Rust
print 'message'
print('message')
print needs parentheses.
Python
const y;
const y = 51;
Initialize const.
JavaScript
// comment
/* comment */
Use /* */.
CSS
fn compute() -> i32 {{ 95 }}
fn compute() -> i32 {{ 95 }}
Correct.
Rust
String index = 'test';
String index = "test";
Double quotes.
Java
p {{ color: red }}
p {{ color: red; }}
Add semicolon.
CSS
$foo = 100; if ($foo = 100) {{}}
$foo = 100; if ($foo == 100) {{}}
Use ==.
PHP
[16, 16, 38
[16, 16, 38]
Close bracket.
Ruby
if item = 15 {{}}
if item == 15 {{}}
Use ==.
Swift
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
def baz(): print('info')
def baz(): print('info')
Indent function body.
Python
val temp: Int = 'data'
val temp: String = 'data'
Fix type.
Kotlin
const obj:Person = {{name:'info'}};
const obj:Person = {{name:'info', age:6}};
Add missing property.
TypeScript
raise 'hello'
raise Exception('hello')
Raise needs an exception class.
Python
let num = 'value'
let num = "value"
Double quotes.
Swift
if c = 8:
if c == 8:
Use == for comparison.
Python
$values[70]
if ($values.Count -gt 70) {{ $values[70] }}
Check bounds.
PowerShell
if ($b = 31)
if ($b == 31)
Use ==.
Perl
int* user = nullptr; *user=5;
int* user = new int; *user=5;
Allocate memory.
C++
cin >> b cout << b;
cin >> b; cout << b;
Add semicolon.
C++
function render(): void {{ return 11; }}
function render(): number {{ return 11; }}
Return type mismatch.
TypeScript
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
class Product {{ int count; }} obj.count=5;
class Product {{ public int count; }} obj.count=5;
Make field public.
Java
if [ $c = 3 ]; then
if [ "$c" = 3 ]; then
Quote variable.
Shell
else print('data')
else: print('data')
Colon after else.
Python
fmt.Println 'output'
fmt.Println('output')
Missing parentheses.
Go
x := 38
x := 38
Correct.
Go
if (c = 26) {{}}
if (c === 26) {{}}
Use === for equality.
JavaScript
arr(37)
if length(arr) >= 37, arr(37), end
Check length.
MATLAB
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
if result = 1
if result == 1
Use ==.
Go
compute
compute()
Add parentheses.
Kotlin
void compute(); int main(){{compute();}}
void compute(); // prototype int main(){{compute();}}
Declare before use.
C++
#footer {{ color: green; }}
#footer {{ color: green; }}
Correct.
CSS
if temp = 93
if temp == 93
Use ==.
MATLAB
'test' + 64
'test' + str(64)
Can't add int to string.
Python