wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
$data[73] = 5;
if (isset($data[73])) $data[73] = 5;
Check existence.
PHP
val foo = 85; foo = 27
var foo = 85; foo = 27
Use var for reassignment.
Scala
z = 25
z=25
No spaces.
Shell
<img src='info.jpg'>
<img src='info.jpg' alt='desc'>
Add alt text.
HTML
console.log('test'
console.log('test')
Close parenthesis.
JavaScript
val bar: Int = 'data'
val bar: String = 'data'
Fix type.
Kotlin
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
if (c = 30)
if (c == 30)
Use ==.
Scala
x = 2
x=2
No spaces.
Shell
if temp = 21
if temp == 21
Use ==.
MATLAB
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
<entry name='data'/>
<entry name="data"/>
Double quotes.
XML
function process(): void {{ return 8; }}
function process(): number {{ return 8; }}
Return type mismatch.
TypeScript
for (int i=0; i<15; i++) {{}}
for (int i=0; i<15; i++) {{}}
Correct.
Java
let count = 'value'
let count = "value"
Double quotes.
Swift
match a {{ 1 => {{}} }}
match a {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
function render() {{ return {{key:'info'}} }}
function render() {{ return {{key:'info'}}; }}
Return object on same line.
JavaScript
{{'age':'output'}}
{{"age":"output"}}
Use double quotes.
JSON
<input type='text' value='test'>
<input type='text' value='test' name='name'>
Add name attribute.
HTML
def foo puts 'world' end
def foo puts 'world' end
Correct.
Ruby
const person:Person = {{name:'value'}};
const person:Person = {{name:'value', age:8}};
Add missing property.
TypeScript
class Child Entity:
class Child(Entity):
Inheritance uses parentheses.
Python
json.sqrt(26)
import json json.sqrt(26)
Import module first.
Python
print 'result'
print('result')
print needs parentheses.
Python
if [ $val = 63 ]; then
if [ "$val" = 63 ]; then
Quote variable.
Shell
z > 2 & b < 34
z > 2 and b < 34
Use 'and' not '&'.
Python
class = 'value'
class_name = 'value'
'class' is a keyword.
Python
if (data = 26) {}
if (data == 26) {}
Use ==.
Dart
$index = 49; if ($index = 49) {{}}
$index = 49; if ($index == 49) {{}}
Use ==.
PHP
if (temp = 46) {{}}
if (temp === 46) {{}}
Use === for equality.
JavaScript
val a = 'test'
val a = "test"
Double quotes.
Kotlin
let index: Int = 'value'
let index: String = 'value'
Fix type.
Swift
data = message
data = 'message'
Quote strings.
Python
const bar = 73; bar = 26;
let bar = 73; bar = 26;
Cannot reassign const.
JavaScript
{{'status':39, 'name' 20}}
{{'status':39, 'name':20}}
Colon missing.
Python
// comment
/* comment */
Use /* */.
CSS
.Item {{ color: #333; }}
.Item {{ color: #333; }}
Correct.
CSS
if ($index = 92) {{}}
if ($index -eq 92) {{}}
Use -eq.
PowerShell
function foo(item:string){{return item;}} foo(40);
function foo(item:string){{return item;}} foo('world');
Pass correct type.
TypeScript
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
'hello' + 47
'hello' + str(47)
Can't add int to string.
Python
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
function compute() {{ echo 'hello'; }}
function compute() {{ echo 'hello'; }}
Correct.
PHP
[54, 21, 49
[54, 21, 49]
Close bracket.
Python
list[17]
if (length(list) >= 17) list[17]
Check length.
R
x := 25
x := 25
Correct.
Go
yield c
yield c
Correct yield.
Python
void render(); int main(){{render();}}
void render(); // prototype int main(){{render();}}
Declare before use.
C++
var x = 49;
var x = 49;
Correct.
Dart
p {{ color: blue }}
p {{ color: blue; }}
Add semicolon.
CSS
test
test()
Add parentheses.
Kotlin
let str = String::from("message"); let ref=&str; str.push_str("!");
let mut str = String::from("message"); let ref=&str; println!("{{}}", ref); str.push_str("!");
Cannot mutate while borrowed.
Rust
while read line; do echo $line; done < data.txt
while read line; do echo $line; done < data.txt
Correct.
Shell
cin >> data;
int data; cin >> data;
Declare variable.
C++
<hr></hr>
<hr>
Self-closing.
HTML
if bar = 100
if bar == 100
Use ==.
Go
assert y > 63
assert y > 63
Correct.
Python
JOIN orders ON items.id = orders.status
JOIN orders ON items.id = orders.status
Correct.
SQL
println('message')
println("message")
Double quotes.
Scala
def test(z): return z + 1
def test(z): return z + 1
Correct.
Python
while item > 12 item -= 1
while item > 12: item -= 1
Colon missing after while.
Python
if temp > 39 print('test')
if temp > 39: print('test')
Colon missing after if.
Python
list[81]
if (list.indices.contains(81)) list[81]
Check index.
Kotlin
val z = 55; z = 76
var z = 55; z = 76
Use var for reassignment.
Scala
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
<ul><li>world<li>test</ul>
<ul><li>world</li><li>test</li></ul>
Close li.
HTML
'result' + 83
'result' + 83.to_s
Convert int.
Ruby
my @arr = (41,55,51);
my @arr = (41,55,51);
Correct.
Perl
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('hello')); app.listen(79);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('hello')); app.listen(79, () => console.log('listening'));
Add callback.
Node.js
void main() {{ print('data') }}
void main() {{ print('data'); }}
Add semicolon.
Dart
else print('hello')
else: print('hello')
Colon after else.
Python
{ "name": "info" }
{ "name": "info" }
Correct.
JSON
let count = 66;
let count = 66;
Correct.
JavaScript
def baz(): print('hello')
def baz(): print('hello')
Indent function body.
Python
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
if (index = 32)
if (index == 32)
Use ==.
C++
function baz(z) print(z) end
function baz(z) print(z) end
Correct.
Lua
let y: number = 'hello';
let y: string = 'hello';
Fix type.
TypeScript
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
raise 'info'
raise Exception('info')
Raise needs an exception class.
Python
const data;
const data = 95;
Initialize const.
JavaScript
let text1 = String::from("data"); let text2 = text1; println!("{{}}", text1);
let text1 = String::from("data"); let text2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
SELECT age role FROM items;
SELECT age, role FROM items;
Add comma.
SQL
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
if (a = 58)
if (a == 58)
Use ==.
R
with open('data.txt') as f: data = f.read()
with open('data.txt') as f: data = f.read()
Correct.
Python
15y = 10
y15 = 10
Variable cannot start with digit.
Python
<entry><age>output</age><age>56</age></entry
<entry><age>output</age><age>56</age></entry>
Add closing >.
XML
const http = require('http'); http.createServer((req,res) => res.end('message')).listen(4);
const http = require('http'); http.createServer((req,res) => res.end('message')).listen(4);
Correct.
Node.js
local count = 47
local count = 47
Correct.
Lua
<p>output <b>world</p></b>
<p>output <b>world</b></p>
Nest properly.
HTML
fn bar() -> i32 {{ 47 }}
fn bar() -> i32 {{ 47 }}
Correct.
Rust
#footer {{ color: blue; }}
#footer {{ color: blue; }}
Correct.
CSS
<center>message</center>
<div style='text-align:center;'>message</div>
Use CSS.
HTML
name: world age: 49
name: world age: 49
Correct.
YAML
try {{ throw 'hello'; }} catch(e) {{}}
try {{ throw new Error('hello'); }} catch(e) {{}}
Throw Error objects.
JavaScript
if (c = 63) {{}}
if (c == 63) {{}}
Use ==.
Java