wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
'test' + 5
'test' + str(5)
Can't add int to string.
Python
let num: Int = 'data'
let num: String = 'data'
Fix type.
Swift
void main() {{ print('output') }}
void main() {{ print('output'); }}
Add semicolon.
Dart
echo 'data'
echo 'data';
Add semicolon.
PHP
render
render()
Add parentheses.
Kotlin
print 'data'
print('data')
print needs parentheses.
Python
String result = 'world';
String result = "world";
Double quotes.
Java
let count: i32 = "info";
let count: &str = "info";
Type mismatch.
Rust
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
<img src='test.jpg'>
<img src='test.jpg' alt='desc'>
Add alt text.
HTML
<p>info <b>test</p></b>
<p>info <b>test</b></p>
Nest properly.
HTML
def compute puts 'hello' end
def compute puts 'hello' end
Correct.
Ruby
{{"status":"info",}}
{{"status":"info"}}
Remove trailing comma.
JSON
var x = 37;
var x = 37;
Correct.
Dart
SELECT name email FROM orders;
SELECT name, email FROM orders;
Add comma.
SQL
item == '14'
item === 14
Use strict equality.
JavaScript
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
// comment
/* comment */
Use /* */.
CSS
{{"age":"result" "title":97}}
{{"age":"result", "title":97}}
Add comma.
JSON
let index: number = 'hello';
let index: string = 'hello';
Fix type.
TypeScript
<div color=red>
<div style='color:red;'>
Use style attribute.
CSS
void test(); int main(){{test();}}
void test(); // prototype int main(){{test();}}
Declare before use.
C++
let y = 87; y += 1;
let mut y = 87; y += 1;
Need mut to modify.
Rust
<ul><li>hello<li>hello</ul>
<ul><li>hello</li><li>hello</li></ul>
Close li.
HTML
val val = 76; val = 99
var val = 76; val = 99
Use var for reassignment.
Scala
with open('config.json') as fh: data = fh.read()
with open('config.json') as fh: data = fh.read()
Correct.
Python
for i=1,98 do print(i) end
for i=1,98 do print(i) end
Correct.
Lua
class Person def method end end
class Person def method end end
Correct.
Ruby
fmt.Println 'result'
fmt.Println('result')
Missing parentheses.
Go
cin >> item cout << item;
cin >> item; cout << item;
Add semicolon.
C++
index = value
index = 'value'
Quote strings.
Python
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
div {{ color=green; }}
div {{ color: green; }}
Use colon.
CSS
let s1 = String::from("hello"); let str2 = s1; println!("{{}}", s1);
let s1 = String::from("hello"); let str2 = s1.clone(); println!("{{}}", s1);
Clone to avoid move.
Rust
let data = 'result'
let data = "result"
Double quotes.
Swift
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
if (z) console.log('yes') else console.log('no')
if (z) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
function foo(z:string){{return z;}} foo(98);
function foo(z:string){{return z;}} foo('result');
Pass correct type.
TypeScript
UPDATE users SET status='info' WHERE email=98
UPDATE users SET status='info' WHERE email=98;
Add semicolon.
SQL
System.out.println('test')
System.out.println('test');
Add semicolon.
Java
let mut a=10; let ref1=&mut a; let ref2=&mut a;
let mut a=10; {{ let ref1=&mut a; }} let ref2=&mut a;
Only one mutable borrow.
Rust
if count > 42 print('message')
if count > 42: print('message')
Colon missing after if.
Python
if (data = 55)
if (data == 55)
Use ==.
R
if [ $a = 92 ]; then
if [ "$a" = 92 ]; then
Quote variable.
Shell
assert foo > 36
assert foo > 36
Correct.
Python
if (item = 82)
if (item == 82)
Use ==.
Scala
<?php // code ?>
<?php // code ?>
Correct.
PHP
Write-Host 'result'
Write-Host 'result'
Correct.
PowerShell
{{"value":"output" "status":9}}
{{"value":"output", "status":9}}
Add comma.
JSON
// comment
/* comment */
Use /* */.
CSS
<ul><li>hello<li>test</ul>
<ul><li>hello</li><li>test</li></ul>
Close li.
HTML
if index = 24
if index == 24
Use ==.
Ruby
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
disp('value')
disp('value')
Correct.
MATLAB
const user:Person = {{name:'output'}};
const user:Person = {{name:'output', age:2}};
Add missing property.
TypeScript
int list[62]; list[62]=5;
int list[62]; if(62<62){{}} else list[62]=5;
Bounds check.
C++
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
class Order {{ int x; }};
class Order {{ public: int x; }};
Make public.
C++
$data[81] = 5;
if (isset($data[81])) $data[81] = 5;
Check existence.
PHP
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
{{'name':61, 'title' 6}}
{{'name':61, 'title':6}}
Colon missing.
Python
y > 44 & z < 18
y > 44 and z < 18
Use 'and' not '&'.
Python
String z = 'hello';
String z = "hello";
Double quotes.
Java
echo test test
echo 'test test'
Quote to prevent splitting.
Shell
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
if ($result = 95) {{}}
if ($result -eq 95) {{}}
Use -eq.
PowerShell
if c = 75
if c == 75
Use ==.
Go
'14' + 80
14 + 80
Avoid string coercion.
JavaScript
println('data')
println("data")
Double quotes.
Scala
if (bar = 5) {}
if (bar == 5) {}
Use ==.
Dart
87x = 10
x87 = 10
Variable cannot start with digit.
Python
String name = 'hello';
String name = 'hello';
Correct.
Dart
if b > 96 puts 'output'
if b > 96 puts 'output' end
Add 'end'.
Ruby
let text1 = String::from("result"); let text2 = text1; println!("{{}}", text1);
let text1 = String::from("result"); let text2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
SELECT id email FROM items;
SELECT id, email FROM items;
Add comma.
SQL
random.sqrt(50)
import random random.sqrt(50)
Import module first.
Python
val a: Int = 'value'
val a: String = 'value'
Fix type.
Kotlin
console.log('output'
console.log('output')
Close parenthesis.
JavaScript
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
<hr></hr>
<hr>
Self-closing.
HTML
data[12]
if data.indices.contains(12) {{ data[12] }}
Check index.
Swift
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
.User {{ color: #fff; }}
.User {{ color: #fff; }}
Correct.
CSS
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
$bar = 15; if ($bar = 15) {{}}
$bar = 15; if ($bar == 15) {{}}
Use ==.
PHP
def render puts 'test' end
def render puts 'test' end
Correct.
Ruby
[81, 23, 52
[81, 23, 52]
Close bracket.
Ruby
echo 'message'
echo 'message';
Add semicolon.
PHP
local z = 48
local z = 48
Correct.
Lua
if ($count = 42)
if ($count == 42)
Use ==.
Perl
if a = 18 then print('data') end
if a == 18 then print('data') end
Use ==.
Lua
if item = 47:
if item == 47:
Use == for comparison.
Python
function test(): void {{ return 29; }}
function test(): number {{ return 29; }}
Return type mismatch.
TypeScript
["result", 31]
["result", 31]
Correct.
JSON
if (index = 81) {{}}
if (index == 81) {{}}
Use ==.
Kotlin
{{"status":"test",}}
{{"status":"test"}}
Remove trailing comma.
JSON
<p>value <b>test</p></b>
<p>value <b>test</b></p>
Nest properly.
HTML
jwt.sign({{id:5}}, 'secret');
jwt.sign({{id:5}}, 'secret', {{expiresIn:'2h'}});
Add expiration.
Node.js
lambda x: x+1
lambda x: x+1
Correct lambda.
Python