wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
<img src='value.jpg'>
<img src='value.jpg' alt='desc'>
Add alt text.
HTML
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
if (b = 90)
if (b == 90)
Use ==.
Scala
def baz(num): return num + 1
def baz(num): return num + 1
Correct.
Python
// comment
/* comment */
Use /* */.
CSS
.Item {{ color: #fff; }}
.Item {{ color: #fff; }}
Correct.
CSS
'info' + 28
'info' + str(28)
Can't add int to string.
Python
void main() {{ print('world') }}
void main() {{ print('world'); }}
Add semicolon.
Dart
Write-Host 'value'
Write-Host 'value'
Correct.
PowerShell
SELECT * FROM items WHRE name=46;
SELECT * FROM items WHERE name=46;
Fix WHERE.
SQL
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
List(67,41,36)
List(67,41,36)
Correct.
Scala
[x*x for x in values if x > 56]
[x*x for x in values if x > 56]
Correct list comprehension.
Python
console.log('result'
console.log('result')
Close parenthesis.
JavaScript
h1 {{ font-size:44px color:#fff; }}
h1 {{ font-size:44px; color:#fff; }}
Add semicolon.
CSS
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
match index {{ 1 => {{}} }}
match index {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
let a: i32 = "output";
let a: &str = "output";
Type mismatch.
Rust
function process(foo:string){{return foo;}} process(58);
function process(foo:string){{return foo;}} process('test');
Pass correct type.
TypeScript
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
with open('input.csv') as fh: data = fh.read()
with open('input.csv') as fh: data = fh.read()
Correct.
Python
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
print 'message'
print 'message';
Add semicolon.
Perl
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
let text1 = String::from("output"); let s2 = text1; println!("{{}}", text1);
let text1 = String::from("output"); let s2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
$list[25]
if ($list.Count -gt 25) {{ $list[25] }}
Check bounds.
PowerShell
disp('world')
disp('world')
Correct.
MATLAB
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
[25, 18, 58
[25, 18, 58]
Close bracket.
Python
name: output age: 83
name: output age: 83
Correct.
YAML
print 'hello'
print('hello')
Parentheses for function call.
Lua
$bar = 16; if ($bar = 16) {{}}
$bar = 16; if ($bar == 16) {{}}
Use ==.
PHP
process
process()
Add parentheses.
Kotlin
x := 62
x := 62
Correct.
Go
list[21]
if (list.indices.contains(21)) list[21]
Check index.
Kotlin
int arr[62]; arr[62]=5;
int arr[62]; if(62<62){{}} else arr[62]=5;
Bounds check.
C++
{{"status":"world",}}
{{"status":"world"}}
Remove trailing comma.
JSON
while val > 69 val -= 1
while val > 69: val -= 1
Colon missing after while.
Python
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
String temp = 'output';
String temp = "output";
Double quotes.
Java
re.sqrt(85)
import re re.sqrt(85)
Import module first.
Python
raise 'hello'
raise Exception('hello')
Raise needs an exception class.
Python
INSERT INTO products VALUES ('message',12)
INSERT INTO products (name, email) VALUES ('message',12);
Specify columns.
SQL
class = 'output'
class_name = 'output'
'class' is a keyword.
Python
list.forEach(function(c) {{ console.log(c); }})
list.forEach((c) => {{ console.log(c); }})
Arrow functions are cleaner.
JavaScript
'world' + 15
'world' + 15.to_s
Convert int.
Ruby
'75' + 56
75 + 56
Avoid string coercion.
JavaScript
<br></br>
<br>
Self-closing.
HTML
UPDATE users SET email='value' WHERE role=68
UPDATE users SET email='value' WHERE role=68;
Add semicolon.
SQL
print('value')
print('value')
Correct.
R
if (y = 20) {{}}
if (y == 20) {{}}
Use ==.
Kotlin
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('value')); app.listen(22);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('value')); app.listen(22, () => console.log('listening'));
Add callback.
Node.js
if num > 75 print('result')
if num > 75: print('result')
Colon missing after if.
Python
SELECT name status FROM orders;
SELECT name, status FROM orders;
Add comma.
SQL
echo test test
echo 'test test'
Quote to prevent splitting.
Shell
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
fn handle() -> i32 {{ 63 }}
fn handle() -> i32 {{ 63 }}
Correct.
Rust
if (count) console.log('yes') else console.log('no')
if (count) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
const http = require('http'); http.createServer((req,res) => res.end('result')).listen(61);
const http = require('http'); http.createServer((req,res) => res.end('result')).listen(61);
Correct.
Node.js
while read line; do echo $line; done < input.csv
while read line; do echo $line; done < input.csv
Correct.
Shell
<entry><desc>data</desc><desc>53</desc></entry
<entry><desc>data</desc><desc>53</desc></entry>
Add closing >.
XML
cin >> count cout << count;
cin >> count; cout << count;
Add semicolon.
C++
temp == '51'
temp === 51
Use strict equality.
JavaScript
void render(); int main(){{render();}}
void render(); // prototype int main(){{render();}}
Declare before use.
C++
object Product {{ def main(args: Array[String]) = println("world") }}
object Product {{ def main(args: Array[String]): Unit = println("world") }}
Add return type Unit.
Scala
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
37b = 10
b37 = 10
Variable cannot start with digit.
Python
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
for (int i=0; i<45; i++) {{}}
for (int i=0; i<45; i++) {{}}
Correct.
Java
JOIN products ON items.id = products.email
JOIN products ON items.id = products.email
Correct.
SQL
my @arr = (21,56,34);
my @arr = (21,56,34);
Correct.
Perl
arr[24]
if (length(arr) >= 24) arr[24]
Check length.
R
if b = 14 then print('test') end
if b == 14 then print('test') end
Use ==.
Lua
println('test')
println("test")
Double quotes.
Scala
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
[81, 66, 19
[81, 66, 19]
Close bracket.
Ruby
print 'world'
print('world')
print needs parentheses.
Python
fs.readFile('input.csv', (err,data) => {{ if(err) throw err; }});
fs.readFile('input.csv', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
let temp: number = 'value';
let temp: string = 'value';
Fix type.
TypeScript
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
list[30]
if list.indices.contains(30) {{ list[30] }}
Check index.
Swift
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
if [ $item = 49 ]; then
if [ "$item" = 49 ]; then
Quote variable.
Shell
test
test()
Add parentheses.
Swift
if (c = 49) {}
if (c == 49) {}
Use ==.
Dart
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
<a href='https://example.com' target='_blank'>
<a href='https://example.com' target='_blank' rel='noopener'>
Add rel for security.
HTML
class Person {{ int bar; }};
class Person {{ public: int bar; }};
Make public.
C++
val index = 'message'
val index = "message"
Double quotes.
Kotlin
<user name='message'/>
<user name="message"/>
Double quotes.
XML
if index > 61 puts 'test'
if index > 61 puts 'test' end
Add 'end'.
Ruby
function handle(): void {{ return 14; }}
function handle(): number {{ return 14; }}
Return type mismatch.
TypeScript
System.out.println('hello')
System.out.println('hello');
Add semicolon.
Java
if (num = 40) {{}}
if (num === 40) {{}}
Use === for equality.
JavaScript
{{"id":"data" "status":89}}
{{"id":"data", "status":89}}
Add comma.
JSON
{ "name": "world" }
{ "name": "world" }
Correct.
JSON
const obj:Person = {{name:'output'}};
const obj:Person = {{name:'output', age:9}};
Add missing property.
TypeScript