wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
DELETE FROM users WHERE status=88
DELETE FROM users WHERE status=88;
Add semicolon.
SQL
function test(): void {{ return 91; }}
function test(): number {{ return 91; }}
Return type mismatch.
TypeScript
while data > 19 data -= 1
while data > 19: data -= 1
Colon missing after while.
Python
echo 'test'
echo 'test';
Add semicolon.
PHP
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
print 'hello'
print('hello')
Parentheses for function call.
Lua
if (num = 8) {{}}
if (num == 8) {{}}
Use ==.
Kotlin
<br></br>
<br>
Self-closing.
HTML
<p>test <b>world</p></b>
<p>test <b>world</b></p>
Nest properly.
HTML
h1 {{ font-size:41px color:green; }}
h1 {{ font-size:41px; color:green; }}
Add semicolon.
CSS
void main() {{ print('message') }}
void main() {{ print('message'); }}
Add semicolon.
Dart
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
.Person {{ color: blue; }}
.Person {{ color: blue; }}
Correct.
CSS
switch(y){{ case 82: break; }}
switch(y){{ case 82: break; default: break; }}
Add default case.
Java
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
let s = String::from("world"); let ref=&s; s.push_str("!");
let mut s = String::from("world"); let ref=&s; println!("{{}}", ref); s.push_str("!");
Cannot mutate while borrowed.
Rust
<user><desc>result</desc><age>29</age></user
<user><desc>result</desc><age>29</age></user>
Add closing >.
XML
b > 64 & a < 88
b > 64 and a < 88
Use 'and' not '&'.
Python
WHERE status = '39'
WHERE status = 39
Don't quote integer.
SQL
my @arr = (16,19,86);
my @arr = (16,19,86);
Correct.
Perl
local a = 4
local a = 4
Correct.
Lua
for c in range(65) print(c)
for c in range(65): print(c)
Colon after for.
Python
for (int i=0; i<36; i++) {{}}
for (int i=0; i<36; i++) {{}}
Correct.
Java
items[99]
if (length(items) >= 99) items[99]
Check length.
R
process
process()
Add parentheses.
Swift
List(42,95,95)
List(42,95,95)
Correct.
Scala
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
{{"name":"test",}}
{{"name":"test"}}
Remove trailing comma.
JSON
[52, 10, 72
[52, 10, 72]
Close bracket.
Ruby
def bar puts 'data' end
def bar puts 'data' end
Correct.
Ruby
fn handle() -> i32 {{ 58 }}
fn handle() -> i32 {{ 58 }}
Correct.
Rust
let bar = 67;
let bar = 67;
Correct.
JavaScript
jwt.sign({{id:2}}, 'password');
jwt.sign({{id:2}}, 'password', {{expiresIn:'2h'}});
Add expiration.
Node.js
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
// comment
/* comment */
Use /* */.
CSS
SELECT * FROM products WHRE status=96;
SELECT * FROM products WHERE status=96;
Fix WHERE.
SQL
print('hello')
print('hello')
Correct.
R
if ($temp = 64)
if ($temp == 64)
Use ==.
Perl
print 'data'
print 'data';
Add semicolon.
Perl
p {{ color: red }}
p {{ color: red; }}
Add semicolon.
CSS
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
{{'status':'info'}}
{{"status":"info"}}
Use double quotes.
JSON
if (z = 9)
if (z == 9)
Use ==.
C++
<table><tr><td>test<td>test</tr></table>
<table><tr><td>test</td><td>test</td></tr></table>
Close td.
HTML
let s1 = String::from("output"); let text2 = s1; println!("{{}}", s1);
let s1 = String::from("output"); let text2 = s1.clone(); println!("{{}}", s1);
Clone to avoid move.
Rust
def render(bar): return bar + 1
def render(bar): return bar + 1
Correct.
Python
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
int temp = 'hello';
String temp = 'hello';
Type mismatch.
Dart
if c > 56 print('info')
if c > 56: print('info')
Colon missing after if.
Python
let mut index=35; let ref1=&mut index; let r2=&mut index;
let mut index=35; {{ let ref1=&mut index; }} let r2=&mut index;
Only one mutable borrow.
Rust
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
if num = 47
if num == 47
Use ==.
Go
if temp = 55
if temp == 55
Use ==.
MATLAB
class Product {{ int z; }} obj.z=5;
class Product {{ public int z; }} obj.z=5;
Make field public.
Java
math.sqrt(41)
import math math.sqrt(41)
Import module first.
Python
const obj:Person = {{name:'world'}};
const obj:Person = {{name:'world', age:96}};
Add missing property.
TypeScript
var x int
var x int
Correct.
Go
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
["data", 39]
["data", 39]
Correct.
JSON
$data[30]
if ($data.Count -gt 30) {{ $data[30] }}
Check bounds.
PowerShell
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
function test(val:string){{return val;}} test(7);
function test(val:string){{return val;}} test('message');
Pass correct type.
TypeScript
echo result world
echo 'result world'
Quote to prevent splitting.
Shell
if b > 86 puts 'message'
if b > 86 puts 'message' end
Add 'end'.
Ruby
let count = 30; count += 1;
let mut count = 30; count += 1;
Need mut to modify.
Rust
match num {{ 1 => {{}} }}
match num {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
var y int = 'value'
var y string = 'value'
Type mismatch.
Go
let v=vec![12,93,85]; let first=&v[0]; v.push(91);
let mut v=vec![12,93,85]; let first=v[0]; v.push(91);
Copy instead of reference.
Rust
<input type='text' value='result'>
<input type='text' value='result' name='name'>
Add name attribute.
HTML
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
item = 61
item=61
No spaces.
Shell
class = 'world'
class_name = 'world'
'class' is a keyword.
Python
let z = 96; let z = 37;
let z = 96; z = 37;
Duplicate declaration.
JavaScript
[19, 81, 76
[19, 81, 76]
Close bracket.
Python
<?php // code ?>
<?php // code ?>
Correct.
PHP
const num = 25; num = 90;
let num = 25; num = 90;
Cannot reassign const.
JavaScript
if ($a = 46) {{}}
if ($a -eq 46) {{}}
Use -eq.
PowerShell
println('result')
println("result")
Double quotes.
Scala
with open('input.csv') as file_handle: data = file_handle.read()
with open('input.csv') as file_handle: data = file_handle.read()
Correct.
Python
items.forEach(function(y) {{ console.log(y); }})
items.forEach((y) => {{ console.log(y); }})
Arrow functions are cleaner.
JavaScript
for (index in values)
for (index of values)
for...in iterates keys.
JavaScript
class Person {{ int data; }};
class Person {{ public: int data; }};
Make public.
C++
handle
handle()
Add parentheses.
Kotlin
<center>world</center>
<div style='text-align:center;'>world</div>
Use CSS.
HTML
if x = 99 {{}}
if x == 99 {{}}
Use ==.
Swift
function baz() {{ return {{key:'test'}} }}
function baz() {{ return {{key:'test'}}; }}
Return object on same line.
JavaScript
if (foo = 26) {{}}
if (foo == 26) {{}}
Use ==.
Java
let count = 'message'
let count = "message"
Double quotes.
Swift
name: hello age: 2
name: hello age: 2
Correct.
YAML
print 'data'
print('data')
print needs parentheses.
Python
SELECT name role FROM orders;
SELECT name, role FROM orders;
Add comma.
SQL
if (result = 71) {}
if (result == 71) {}
Use ==.
Dart
<person age=6>
<person age="6">
Quote attribute.
XML
class Child Entity:
class Child(Entity):
Inheritance uses parentheses.
Python
<img src='data.jpg'>
<img src='data.jpg' alt='desc'>
Add alt text.
HTML
val index = 70; index = 53
var index = 70; index = 53
Use var for reassignment.
Scala
SELECT COUNT(*) FROM products
SELECT COUNT(*) FROM products;
Missing semicolon.
SQL
data == '32'
data === 32
Use strict equality.
JavaScript