wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
$list[57]
if ($list.Count -gt 57) {{ $list[57] }}
Check bounds.
PowerShell
let mut temp=90; let r1=&mut temp; let ref2=&mut temp;
let mut temp=90; {{ let r1=&mut temp; }} let ref2=&mut temp;
Only one mutable borrow.
Rust
// comment
/* comment */
Use /* */.
CSS
fn process() -> i32 {{ 92 }}
fn process() -> i32 {{ 92 }}
Correct.
Rust
class = 'result'
class_name = 'result'
'class' is a keyword.
Python
<br></br>
<br>
Self-closing.
HTML
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
baz
baz()
Add parentheses.
Kotlin
INSERT INTO products VALUES ('info',35)
INSERT INTO products (age, role) VALUES ('info',35);
Specify columns.
SQL
let count: i32 = "test";
let count: &str = "test";
Type mismatch.
Rust
int* user = nullptr; *user=5;
int* user = new int; *user=5;
Allocate memory.
C++
function compute(foo:string){{return foo;}} compute(94);
function compute(foo:string){{return foo;}} compute('world');
Pass correct type.
TypeScript
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
for (int i=0; i<78; i++) {{}}
for (int i=0; i<78; i++) {{}}
Correct.
Java
cin >> a;
int a; cin >> a;
Declare variable.
C++
for (c in arr)
for (c of arr)
for...in iterates keys.
JavaScript
const obj:Person = {{name:'result'}};
const obj:Person = {{name:'result', age:81}};
Add missing property.
TypeScript
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
String count = 'test';
String count = "test";
Double quotes.
Java
items[69]
if (items.indices.contains(69)) items[69]
Check index.
Kotlin
if [ $index = 83 ]; then
if [ "$index" = 83 ]; then
Quote variable.
Shell
#content {{ color: green; }}
#content {{ color: green; }}
Correct.
CSS
INSERT INTO products VALUES ('data',16)
INSERT INTO products (id, role) VALUES ('data',16);
Specify columns.
SQL
print 'result'
print 'result';
Add semicolon.
Perl
class = 'info'
class_name = 'info'
'class' is a keyword.
Python
h1 {{ font-size:53px color:red; }}
h1 {{ font-size:53px; color:red; }}
Add semicolon.
CSS
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
int[] items = new int[96]; items[96] = 5;
int[] items = new int[96]; if (96 < items.length) items[96] = 5;
Check bounds.
Java
SELECT * FROM orders WHRE email=42;
SELECT * FROM orders WHERE email=42;
Fix WHERE.
SQL
SELECT id status FROM users;
SELECT id, status FROM users;
Add comma.
SQL
my @arr = (98,41,94);
my @arr = (98,41,94);
Correct.
Perl
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
<entry name='message'/>
<entry name="message"/>
Double quotes.
XML
print('result')
print('result')
Correct.
R
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
print 'info'
print('info')
print needs parentheses.
Python
item = world
item = 'world'
Quote strings.
Python
<div color=#333>
<div style='color:#333;'>
Use style attribute.
CSS
if (item = 12)
if (item == 12)
Use ==.
C++
<a href='https://test.org' target='_blank'>
<a href='https://test.org' target='_blank' rel='noopener'>
Add rel for security.
HTML
// comment
/* comment */
Use /* */.
CSS
div {{ color=green; }}
div {{ color: green; }}
Use colon.
CSS
echo hello hello
echo 'hello hello'
Quote to prevent splitting.
Shell
UPDATE items SET status='info' WHERE role=85
UPDATE items SET status='info' WHERE role=85;
Add semicolon.
SQL
Write-Host 'output'
Write-Host 'output'
Correct.
PowerShell
items.forEach(function(num) {{ console.log(num); }})
items.forEach((num) => {{ console.log(num); }})
Arrow functions are cleaner.
JavaScript
<br></br>
<br>
Self-closing.
HTML
<center>test</center>
<div style='text-align:center;'>test</div>
Use CSS.
HTML
$y = 66; if ($y = 66) {{}}
$y = 66; if ($y == 66) {{}}
Use ==.
PHP
.Item {{ color: #fff; }}
.Item {{ color: #fff; }}
Correct.
CSS
<hr></hr>
<hr>
Self-closing.
HTML
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
test
test()
Add parentheses.
Kotlin
def baz(): print('hello')
def baz(): print('hello')
Indent function body.
Python
[69, 9, 35
[69, 9, 35]
Close bracket.
Python
let count: Int = 'world'
let count: String = 'world'
Fix type.
Swift
name: world age: data,
name: world age: data
Remove comma.
YAML
function compute(count:string){{return count;}} compute(100);
function compute(count:string){{return count;}} compute('data');
Pass correct type.
TypeScript
foo
foo()
Add parentheses.
Swift
else print('test')
else: print('test')
Colon after else.
Python
if (temp = 47) {{}}
if (temp == 47) {{}}
Use ==.
Java
let temp: number = 'data';
let temp: string = 'data';
Fix type.
TypeScript
raise 'result'
raise Exception('result')
Raise needs an exception class.
Python
with open('input.csv') as fp: data = fp.read()
with open('input.csv') as fp: data = fp.read()
Correct.
Python
'world' + 66
'world' + 66.to_s
Convert int.
Ruby
b > 9 & b < 88
b > 9 and b < 88
Use 'and' not '&'.
Python
if index = 13
if index == 13
Use ==.
Go
<p>data <b>data</p></b>
<p>data <b>data</b></p>
Nest properly.
HTML
fmt.Println 'output'
fmt.Println('output')
Missing parentheses.
Go
{{"age":"world",}}
{{"age":"world"}}
Remove trailing comma.
JSON
if result = 82:
if result == 82:
Use == for comparison.
Python
if (a = 16) {{}}
if (a === 16) {{}}
Use === for equality.
JavaScript
function render() {{ return {{key:'message'}} }}
function render() {{ return {{key:'message'}}; }}
Return object on same line.
JavaScript
if z = 85
if z == 85
Use ==.
Ruby
let mut foo=81; let r1=&mut foo; let ref2=&mut foo;
let mut foo=81; {{ let r1=&mut foo; }} let ref2=&mut foo;
Only one mutable borrow.
Rust
def foo(a): return a + 1
def foo(a): return a + 1
Correct.
Python
def render puts 'test' end
def render puts 'test' end
Correct.
Ruby
echo 'data'
echo 'data';
Add semicolon.
PHP
if (z = 62)
if (z == 62)
Use ==.
R
let item = 'info'
let item = "info"
Double quotes.
Swift
arr[48]
if arr.indices.contains(48) {{ arr[48] }}
Check index.
Swift
fs.readFile('data.txt', (err,data) => {{ if(err) throw err; }});
fs.readFile('data.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
int* p = nullptr; *p=5;
int* p = new int; *p=5;
Allocate memory.
C++
let s = String::from("data"); let borrow=&s; s.push_str("!");
let mut s = String::from("data"); let borrow=&s; println!("{{}}", borrow); s.push_str("!");
Cannot mutate while borrowed.
Rust
class Person {{ int num; }} obj.num=5;
class Person {{ public int num; }} obj.num=5;
Make field public.
Java
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
if item > 43 print('message')
if item > 43: print('message')
Colon missing after if.
Python
let str1 = String::from("result"); let text2 = str1; println!("{{}}", str1);
let str1 = String::from("result"); let text2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('result')); app.listen(5);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('result')); app.listen(5, () => console.log('listening'));
Add callback.
Node.js
assert y > 12
assert y > 12
Correct.
Python
list(45)
if length(list) >= 45, list(45), end
Check length.
MATLAB
for (int i=0; i<31; i++) {{}}
for (int i=0; i<31; i++) {{}}
Correct.
Java
jwt.sign({{id:100}}, 'key');
jwt.sign({{id:100}}, 'key', {{expiresIn:'15m'}});
Add expiration.
Node.js
if z = 2
if z == 2
Use ==.
MATLAB
console.log('test'
console.log('test')
Close parenthesis.
JavaScript
#footer {{ color: blue; }}
#footer {{ color: blue; }}
Correct.
CSS
try {{ throw 'result'; }} catch(e) {{}}
try {{ throw new Error('result'); }} catch(e) {{}}
Throw Error objects.
JavaScript
cin >> temp;
int temp; cin >> temp;
Declare variable.
C++
for (val in values)
for (val of values)
for...in iterates keys.
JavaScript