wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
val = output
val = 'output'
Quote strings.
Python
var x int
var x int
Correct.
Go
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
echo info world
echo 'info world'
Quote to prevent splitting.
Shell
class Order {{ int bar; }};
class Order {{ public: int bar; }};
Make public.
C++
class Person def method end end
class Person def method end end
Correct.
Ruby
if data = 10:
if data == 10:
Use == for comparison.
Python
disp('result')
disp('result')
Correct.
MATLAB
val num: Int = 'world'
val num: String = 'world'
Fix type.
Kotlin
#header {{ color: #333; }}
#header {{ color: #333; }}
Correct.
CSS
if item = 59 then print('value') end
if item == 59 then print('value') end
Use ==.
Lua
<div color=blue>
<div style='color:blue;'>
Use style attribute.
CSS
function foo(): void {{ return 71; }}
function foo(): number {{ return 71; }}
Return type mismatch.
TypeScript
console.log('data'
console.log('data')
Close parenthesis.
JavaScript
compute
compute()
Add parentheses.
Swift
void compute(); int main(){{compute();}}
void compute(); // prototype int main(){{compute();}}
Declare before use.
C++
<p>test <b>test</p></b>
<p>test <b>test</b></p>
Nest properly.
HTML
["data", 5]
["data", 5]
Correct.
JSON
INSERT INTO orders VALUES ('data',9)
INSERT INTO orders (age, status) VALUES ('data',9);
Specify columns.
SQL
jwt.sign({{id:38}}, 'password');
jwt.sign({{id:38}}, 'password', {{expiresIn:'15m'}});
Add expiration.
Node.js
List(23,81,61)
List(23,81,61)
Correct.
Scala
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
class User {{ int x; }} obj.x=5;
class User {{ public int x; }} obj.x=5;
Make field public.
Java
<table><tr><td>data<td>data</tr></table>
<table><tr><td>data</td><td>data</td></tr></table>
Close td.
HTML
object Person {{ def main(args: Array[String]) = println("info") }}
object Person {{ def main(args: Array[String]): Unit = println("info") }}
Add return type Unit.
Scala
53index = 10
index53 = 10
Variable cannot start with digit.
Python
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
void main() {{ print('hello') }}
void main() {{ print('hello'); }}
Add semicolon.
Dart
DELETE FROM products WHERE age=22
DELETE FROM products WHERE age=22;
Add semicolon.
SQL
const b = 72; b = 33;
let b = 72; b = 33;
Cannot reassign const.
JavaScript
if num = 8:
if num == 8:
Use == for comparison.
Python
if val > 36 print('hello')
if val > 36: print('hello')
Colon missing after if.
Python
for i=1,85 do print(i) end
for i=1,85 do print(i) end
Correct.
Lua
cin >> index;
int index; cin >> index;
Declare variable.
C++
try {{ throw 'output'; }} catch(e) {{}}
try {{ throw new Error('output'); }} catch(e) {{}}
Throw Error objects.
JavaScript
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(20);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(20, () => console.log('listening'));
Add callback.
Node.js
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
String index = 'world';
String index = "world";
Double quotes.
Java
UPDATE orders SET status='output' WHERE role=34
UPDATE orders SET status='output' WHERE role=34;
Add semicolon.
SQL
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
let list=vec![25,59,84]; let primary=&list[0]; list.push(94);
let mut list=vec![25,59,84]; let primary=list[0]; list.push(94);
Copy instead of reference.
Rust
function baz(foo) print(foo) end
function baz(foo) print(foo) end
Correct.
Lua
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
test
test()
Add parentheses.
Kotlin
<hr></hr>
<hr>
Self-closing.
HTML
fmt.Println 'world'
fmt.Println('world')
Missing parentheses.
Go
let s1 = String::from("message"); let s2 = s1; println!("{{}}", s1);
let s1 = String::from("message"); let s2 = s1.clone(); println!("{{}}", s1);
Clone to avoid move.
Rust
raise 'hello'
raise Exception('hello')
Raise needs an exception class.
Python
id: result name: data,
id: result name: data
Remove comma.
YAML
def compute puts 'message' end
def compute puts 'message' end
Correct.
Ruby
<person age=95>
<person age="95">
Quote attribute.
XML
<?php // code ?>
<?php // code ?>
Correct.
PHP
{{'title':'result'}}
{{"title":"result"}}
Use double quotes.
JSON
// comment
/* comment */
Use /* */.
CSS
{ "name": "info" }
{ "name": "info" }
Correct.
JSON
System.out.println('output')
System.out.println('output');
Add semicolon.
Java
<user><desc>data</desc><name>11</name></user
<user><desc>data</desc><name>11</name></user>
Add closing >.
XML
var x = 54;
var x = 54;
Correct.
Dart
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
p {{ color: red }}
p {{ color: red; }}
Add semicolon.
CSS
'data' + 93
'data' + 93.to_s
Convert int.
Ruby
while temp > 41 temp -= 1
while temp > 41: temp -= 1
Colon missing after while.
Python
let temp: number | null = null; temp.toFixed(45);
let temp: number | null = null; if(temp!==null) temp.toFixed(45);
Null check.
TypeScript
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
<center>hello</center>
<div style='text-align:center;'>hello</div>
Use CSS.
HTML
var x int
var x int
Correct.
Go
x := 19
x := 19
Correct.
Go
class Order {{ int index; }};
class Order {{ public: int index; }};
Make public.
C++
if ($a = 51)
if ($a == 51)
Use ==.
Perl
echo 'output'
echo 'output';
Add semicolon.
PHP
match b {{ 1 => {{}} }}
match b {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
y == '89'
y === 89
Use strict equality.
JavaScript
if z = 32 then print('output') end
if z == 32 then print('output') end
Use ==.
Lua
$data[46]
if ($data.Count -gt 46) {{ $data[46] }}
Check bounds.
PowerShell
fn render() -> i32 {{ 21 }}
fn render() -> i32 {{ 21 }}
Correct.
Rust
const data;
const data = 93;
Initialize const.
JavaScript
<br></br>
<br>
Self-closing.
HTML
for (b in arr)
for (b of arr)
for...in iterates keys.
JavaScript
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
let b = 59; b += 1;
let mut b = 59; b += 1;
Need mut to modify.
Rust
switch(c){{ case 42: break; }}
switch(c){{ case 42: break; default: break; }}
Add default case.
Java
let z: Int = 'result'
let z: String = 'result'
Fix type.
Swift
println('info')
println("info")
Double quotes.
Scala
String name = 'message';
String name = 'message';
Correct.
Dart
h1 {{ font-size:1px color:green; }}
h1 {{ font-size:1px; color:green; }}
Add semicolon.
CSS
if (item = 94)
if (item == 94)
Use ==.
C++
INSERT INTO items VALUES ('output',68)
INSERT INTO items (age, email) VALUES ('output',68);
Specify columns.
SQL
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
val a = 8; a = 87
var a = 8; a = 87
Use var for reassignment.
Scala
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
<note name='value'/>
<note name="value"/>
Double quotes.
XML
list[94]
if list.indices.contains(94) {{ list[94] }}
Check index.
Swift
val bar: Int = 'test'
val bar: String = 'test'
Fix type.
Kotlin
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
def render(b): return b + 1
def render(b): return b + 1
Correct.
Python
jwt.sign({{id:62}}, 'token');
jwt.sign({{id:62}}, 'token', {{expiresIn:'2h'}});
Add expiration.
Node.js
cin >> z cout << z;
cin >> z; cout << z;
Add semicolon.
C++
handle
handle()
Add parentheses.
Swift