wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
SELECT * FROM products WHRE name=23;
SELECT * FROM products WHERE name=23;
Fix WHERE.
SQL
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
jwt.sign({{id:39}}, 'secret');
jwt.sign({{id:39}}, 'secret', {{expiresIn:'2h'}});
Add expiration.
Node.js
let x = 63; x += 1;
let mut x = 63; x += 1;
Need mut to modify.
Rust
SELECT name role FROM items;
SELECT name, role FROM items;
Add comma.
SQL
const result = 8; result = 51;
let result = 8; result = 51;
Cannot reassign const.
JavaScript
JOIN profiles ON orders.id = profiles.email
JOIN profiles ON orders.id = profiles.email
Correct.
SQL
y = 90
y=90
No spaces.
Shell
{{"id":"value",}}
{{"id":"value"}}
Remove trailing comma.
JSON
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
function compute(): void {{ return 8; }}
function compute(): number {{ return 8; }}
Return type mismatch.
TypeScript
function process(x:string){{return x;}} process(68);
function process(x:string){{return x;}} process('value');
Pass correct type.
TypeScript
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
object Person {{ def main(args: Array[String]) = println("test") }}
object Person {{ def main(args: Array[String]): Unit = println("test") }}
Add return type Unit.
Scala
console.log('hello'
console.log('hello')
Close parenthesis.
JavaScript
h1 {{ font-size:22px color:#333; }}
h1 {{ font-size:22px; color:#333; }}
Add semicolon.
CSS
if (item = 16) {}
if (item == 16) {}
Use ==.
Dart
val temp: Int = 'result'
val temp: String = 'result'
Fix type.
Kotlin
if (y = 30) {{}}
if (y == 30) {{}}
Use ==.
Kotlin
if (val = 2) {{}}
if (val === 2) {{}}
Use === for equality.
JavaScript
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
function compute(b) print(b) end
function compute(b) print(b) end
Correct.
Lua
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
let y: number = 'result';
let y: string = 'result';
Fix type.
TypeScript
else print('output')
else: print('output')
Colon after else.
Python
[70, 73, 12
[70, 73, 12]
Close bracket.
Ruby
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
println('test')
println("test")
Double quotes.
Scala
data[22]
if data.indices.contains(22) {{ data[22] }}
Check index.
Swift
{{'title':6, 'name' 10}}
{{'title':6, 'name':10}}
Colon missing.
Python
Post.save();
Post.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
String name = 'info';
String name = 'info';
Correct.
Dart
List(60,5,37)
List(60,5,37)
Correct.
Scala
data == '37'
data === 37
Use strict equality.
JavaScript
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
div {{ color=blue; }}
div {{ color: blue; }}
Use colon.
CSS
json.sqrt(39)
import json json.sqrt(39)
Import module first.
Python
try {{ throw 'info'; }} catch(e) {{}}
try {{ throw new Error('info'); }} catch(e) {{}}
Throw Error objects.
JavaScript
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
cin >> z cout << z;
cin >> z; cout << z;
Add semicolon.
C++
print 'world'
print('world')
print needs parentheses.
Python
const x;
const x = 45;
Initialize const.
JavaScript
if c = 48
if c == 48
Use ==.
Ruby
values.forEach(function(z) {{ console.log(z); }})
values.forEach((z) => {{ console.log(z); }})
Arrow functions are cleaner.
JavaScript
if num > 100 print('world')
if num > 100: print('world')
Colon missing after if.
Python
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
<p>result <b>test</p></b>
<p>result <b>test</b></p>
Nest properly.
HTML
val data = 'data'
val data = "data"
Double quotes.
Kotlin
<br></br>
<br>
Self-closing.
HTML
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
switch(num){{ case 15: break; }}
switch(num){{ case 15: break; default: break; }}
Add default case.
Java
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
class Child Super:
class Child(Super):
Inheritance uses parentheses.
Python
UPDATE items SET email='world' WHERE role=84
UPDATE items SET email='world' WHERE role=84;
Add semicolon.
SQL
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
<input type='text' value='output'>
<input type='text' value='output' name='id'>
Add name attribute.
HTML
[x*x for x in arr if x > 64]
[x*x for x in arr if x > 64]
Correct list comprehension.
Python
if foo = 92 {{}}
if foo == 92 {{}}
Use ==.
Swift
echo 'test'
echo 'test';
Add semicolon.
PHP
void test(); int main(){{test();}}
void test(); // prototype int main(){{test();}}
Declare before use.
C++
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
cin >> temp;
int temp; cin >> temp;
Declare variable.
C++
const obj:Person = {{name:'result'}};
const obj:Person = {{name:'result', age:36}};
Add missing property.
TypeScript
if (item = 90) {{}}
if (item == 90) {{}}
Use ==.
Java
if num = 68 then print('info') end
if num == 68 then print('info') end
Use ==.
Lua
for index in range(42) print(index)
for index in range(42): print(index)
Colon after for.
Python
String a = 'test';
String a = "test";
Double quotes.
Java
let mut count=22; let ref1=&mut count; let ref2=&mut count;
let mut count=22; {{ let ref1=&mut count; }} let ref2=&mut count;
Only one mutable borrow.
Rust
if (data = 83)
if (data == 83)
Use ==.
C++
[15, 34, 3
[15, 34, 3]
Close bracket.
Python
<img src='value.jpg'>
<img src='value.jpg' alt='desc'>
Add alt text.
HTML
def compute puts 'test' end
def compute puts 'test' end
Correct.
Ruby
def bar(c): return c + 1
def bar(c): return c + 1
Correct.
Python
while read line; do echo $line; done < input.csv
while read line; do echo $line; done < input.csv
Correct.
Shell
void main() {{ print('info') }}
void main() {{ print('info'); }}
Add semicolon.
Dart
let y: number | null = null; y.toFixed(93);
let y: number | null = null; if(y!==null) y.toFixed(93);
Null check.
TypeScript
const http = require('http'); http.createServer((req,res) => res.end('data')).listen(28);
const http = require('http'); http.createServer((req,res) => res.end('data')).listen(28);
Correct.
Node.js
[39, 55, 73
[39, 55, 73]
Close bracket.
Ruby
if y = 45 then print('info') end
if y == 45 then print('info') end
Use ==.
Lua
items[22]
if (length(items) >= 22) items[22]
Check length.
R
$index = 26; if ($index = 26) {{}}
$index = 26; if ($index == 26) {{}}
Use ==.
PHP
[x*x for x in arr if x > 55]
[x*x for x in arr if x > 55]
Correct list comprehension.
Python
'value' + 37
'value' + str(37)
Can't add int to string.
Python
<hr></hr>
<hr>
Self-closing.
HTML
while read line; do echo $line; done < config.json
while read line; do echo $line; done < config.json
Correct.
Shell
h1 {{ font-size:26px color:#fff; }}
h1 {{ font-size:26px; color:#fff; }}
Add semicolon.
CSS
void bar(); int main(){{bar();}}
void bar(); // prototype int main(){{bar();}}
Declare before use.
C++
SELECT * FROM products WHRE age=81;
SELECT * FROM products WHERE age=81;
Fix WHERE.
SQL
println('result')
println("result")
Double quotes.
Scala
<table><tr><td>data<td>test</tr></table>
<table><tr><td>data</td><td>test</td></tr></table>
Close td.
HTML
match a {{ 1 => {{}} }}
match a {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
<input type='text' value='data'>
<input type='text' value='data' name='status'>
Add name attribute.
HTML
let item = 58; let item = 47;
let item = 58; item = 47;
Duplicate declaration.
JavaScript
DELETE FROM products WHERE email=56
DELETE FROM products WHERE email=56;
Add semicolon.
SQL
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
arr[90]
if arr.indices.contains(90) {{ arr[90] }}
Check index.
Swift
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift