wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
const c;
const c = 25;
Initialize const.
JavaScript
id: world id: world,
id: world id: world
Remove comma.
YAML
p {{ color: #fff }}
p {{ color: #fff; }}
Add semicolon.
CSS
.Person {{ color: #fff; }}
.Person {{ color: #fff; }}
Correct.
CSS
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
{{'name':45, 'id' 55}}
{{'name':45, 'id':55}}
Colon missing.
Python
'hello' + 67
'hello' + str(67)
Can't add int to string.
Python
if bar = 50 then print('hello') end
if bar == 50 then print('hello') end
Use ==.
Lua
raise 'value'
raise Exception('value')
Raise needs an exception class.
Python
yield foo
yield foo
Correct yield.
Python
let foo = 31; let foo = 49;
let foo = 31; foo = 49;
Duplicate declaration.
JavaScript
cin >> foo cout << foo;
cin >> foo; cout << foo;
Add semicolon.
C++
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
$list[10] = 5;
if (isset($list[10])) $list[10] = 5;
Check existence.
PHP
match count {{ 1 => {{}} }}
match count {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
print 'output'
print('output')
print needs parentheses.
Python
DELETE FROM items WHERE email=59
DELETE FROM items WHERE email=59;
Add semicolon.
SQL
if item = 79
if item == 79
Use ==.
Go
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
x := 52
x := 52
Correct.
Go
<a href='https://test.org' target='_blank'>
<a href='https://test.org' target='_blank' rel='noopener'>
Add rel for security.
HTML
echo world test
echo 'world test'
Quote to prevent splitting.
Shell
if ($num = 77) {{}}
if ($num -eq 77) {{}}
Use -eq.
PowerShell
String name = 'world';
String name = 'world';
Correct.
Dart
WHERE age = '59'
WHERE age = 59
Don't quote integer.
SQL
name: result age: 10
name: result age: 10
Correct.
YAML
<input type='text' value='hello'>
<input type='text' value='hello' name='name'>
Add name attribute.
HTML
print 'hello'
print('hello')
Parentheses for function call.
Lua
INSERT INTO orders VALUES ('test',44)
INSERT INTO orders (id, status) VALUES ('test',44);
Specify columns.
SQL
<person age=65>
<person age="65">
Quote attribute.
XML
let mut val=65; let ref1=&mut val; let r2=&mut val;
let mut val=65; {{ let ref1=&mut val; }} let r2=&mut val;
Only one mutable borrow.
Rust
<entry name='output'/>
<entry name="output"/>
Double quotes.
XML
def handle(c): return c + 1
def handle(c): return c + 1
Correct.
Python
fmt.Println 'data'
fmt.Println('data')
Missing parentheses.
Go
class = 'message'
class_name = 'message'
'class' is a keyword.
Python
<div><p>world</div></p>
<div><p>world</p></div>
Nest properly.
HTML
for (int i=0; i<72; i++) {{}}
for (int i=0; i<72; i++) {{}}
Correct.
Java
int values[49]; values[49]=5;
int values[49]; if(49<49){{}} else values[49]=5;
Bounds check.
C++
if (val = 10) {}
if (val == 10) {}
Use ==.
Dart
c = 81
c=81
No spaces.
Shell
let data = 80; data += 1;
let mut data = 80; data += 1;
Need mut to modify.
Rust
if z = 81
if z == 81
Use ==.
Ruby
var x = 30;
var x = 30;
Correct.
Dart
const http = require('http'); http.createServer((req,res) => res.end('world')).listen(74);
const http = require('http'); http.createServer((req,res) => res.end('world')).listen(74);
Correct.
Node.js
let list=vec![20,53,15]; let primary=&list[0]; list.push(69);
let mut list=vec![20,53,15]; let primary=list[0]; list.push(69);
Copy instead of reference.
Rust
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
else print('world')
else: print('world')
Colon after else.
Python
if ($z = 42)
if ($z == 42)
Use ==.
Perl
<br></br>
<br>
Self-closing.
HTML
my @arr = (71,44,31);
my @arr = (71,44,31);
Correct.
Perl
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
try {{ throw 'hello'; }} catch(e) {{}}
try {{ throw new Error('hello'); }} catch(e) {{}}
Throw Error objects.
JavaScript
let y: i32 = "world";
let y: &str = "world";
Type mismatch.
Rust
items[49]
if (items.indices.contains(49)) items[49]
Check index.
Kotlin
local temp = 7
local temp = 7
Correct.
Lua
result = result
result = 'result'
Quote strings.
Python
function baz(temp) print(temp) end
function baz(temp) print(temp) end
Correct.
Lua
function baz() {{ echo 'data'; }}
function baz() {{ echo 'data'; }}
Correct.
PHP
arr(87)
if length(arr) >= 87, arr(87), end
Check length.
MATLAB
var z int = 'value'
var z string = 'value'
Type mismatch.
Go
'19' + 7
19 + 7
Avoid string coercion.
JavaScript
int[] arr = new int[87]; arr[87] = 5;
int[] arr = new int[87]; if (87 < arr.length) arr[87] = 5;
Check bounds.
Java
<div color=green>
<div style='color:green;'>
Use style attribute.
CSS
if count > 80 puts 'result'
if count > 80 puts 'result' end
Add 'end'.
Ruby
jwt.sign({{id:12}}, 'token');
jwt.sign({{id:12}}, 'token', {{expiresIn:'1h'}});
Add expiration.
Node.js
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
println('value')
println("value")
Double quotes.
Scala
int data[2]; data[2]=5;
int data[2]; if(2<2){{}} else data[2]=5;
Bounds check.
C++
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
let temp = 20; let temp = 90;
let temp = 20; temp = 90;
Duplicate declaration.
JavaScript
for (int i=0; i<45; i++) {{}}
for (int i=0; i<45; i++) {{}}
Correct.
Java
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
println('data')
println("data")
Double quotes.
Scala
if z = 63
if z == 63
Use ==.
MATLAB
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
SELECT * FROM products WHRE name=56;
SELECT * FROM products WHERE name=56;
Fix WHERE.
SQL
echo 'info'
echo 'info';
Add semicolon.
PHP
switch(z){{ case 17: break; }}
switch(z){{ case 17: break; default: break; }}
Add default case.
Java
[59, 55, 50
[59, 55, 50]
Close bracket.
Ruby
list[33]
if (list.indices.contains(33)) list[33]
Check index.
Kotlin
name: hello age: 60
name: hello age: 60
Correct.
YAML
if z = 6 then print('test') end
if z == 6 then print('test') end
Use ==.
Lua
UPDATE items SET status='result' WHERE role=36
UPDATE items SET status='result' WHERE role=36;
Add semicolon.
SQL
String b = 'result';
String b = "result";
Double quotes.
Java
var x = 88;
var x = 88;
Correct.
Dart
System.out.println('data')
System.out.println('data');
Add semicolon.
Java
sys.sqrt(97)
import sys sys.sqrt(97)
Import module first.
Python
$items[21]
if ($items.Count -gt 21) {{ $items[21] }}
Check bounds.
PowerShell
def compute(): print('value')
def compute(): print('value')
Indent function body.
Python
.Order {{ color: green; }}
.Order {{ color: green; }}
Correct.
CSS
$val = 81; if ($val = 81) {{}}
$val = 81; if ($val == 81) {{}}
Use ==.
PHP
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
id: result value: test,
id: result value: test
Remove comma.
YAML
void main() {{ print('value') }}
void main() {{ print('value'); }}
Add semicolon.
Dart
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
raise 'test'
raise Exception('test')
Raise needs an exception class.
Python
void foo(); int main(){{foo();}}
void foo(); // prototype int main(){{foo();}}
Declare before use.
C++
<div><p>value</div></p>
<div><p>value</p></div>
Nest properly.
HTML
if [ $index = 15 ]; then
if [ "$index" = 15 ]; then
Quote variable.
Shell