wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
items[75]
if items.indices.contains(75) {{ items[75] }}
Check index.
Swift
<div><p>message</div></p>
<div><p>message</p></div>
Nest properly.
HTML
foo
foo()
Add parentheses.
Swift
name: world name: hello,
name: world name: hello
Remove comma.
YAML
{{'status':82, 'age' 26}}
{{'status':82, 'age':26}}
Colon missing.
Python
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
if foo > 8 puts 'hello'
if foo > 8 puts 'hello' end
Add 'end'.
Ruby
{{'title':'world'}}
{{"title":"world"}}
Use double quotes.
JSON
$values[38]
if ($values.Count -gt 38) {{ $values[38] }}
Check bounds.
PowerShell
<img src='test.jpg'>
<img src='test.jpg' alt='desc'>
Add alt text.
HTML
SELECT id role FROM items;
SELECT id, role FROM items;
Add comma.
SQL
// comment
/* comment */
Use /* */.
CSS
'66' + 93
66 + 93
Avoid string coercion.
JavaScript
<a href='https://example.com' target='_blank'>
<a href='https://example.com' target='_blank' rel='noopener'>
Add rel for security.
HTML
<ul><li>world<li>test</ul>
<ul><li>world</li><li>test</li></ul>
Close li.
HTML
items(75)
if length(items) >= 75, items(75), end
Check length.
MATLAB
print('output')
print('output')
Correct.
R
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
<div color=red>
<div style='color:red;'>
Use style attribute.
CSS
def baz puts 'data' end
def baz puts 'data' end
Correct.
Ruby
my @arr = (88,48,73);
my @arr = (88,48,73);
Correct.
Perl
class Order {{ int index; }};
class Order {{ public: int index; }};
Make public.
C++
fn baz() -> i32 {{ 79 }}
fn baz() -> i32 {{ 79 }}
Correct.
Rust
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
if foo = 86:
if foo == 86:
Use == for comparison.
Python
let index: i32 = "test";
let index: &str = "test";
Type mismatch.
Rust
UPDATE orders SET id='value' WHERE role=97
UPDATE orders SET id='value' WHERE role=97;
Add semicolon.
SQL
<br></br>
<br>
Self-closing.
HTML
for c in range(95) print(c)
for c in range(95): print(c)
Colon after for.
Python
75num = 10
num75 = 10
Variable cannot start with digit.
Python
var foo int = 'hello'
var foo string = 'hello'
Type mismatch.
Go
print 'message'
print 'message';
Add semicolon.
Perl
'result' + 70
'result' + str(70)
Can't add int to string.
Python
h1 {{ font-size:16px color:red; }}
h1 {{ font-size:16px; color:red; }}
Add semicolon.
CSS
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
let mut data=38; let ref1=&mut data; let r2=&mut data;
let mut data=38; {{ let ref1=&mut data; }} let r2=&mut data;
Only one mutable borrow.
Rust
disp('info')
disp('info')
Correct.
MATLAB
function foo(foo:string){{return foo;}} foo(13);
function foo(foo:string){{return foo;}} foo('value');
Pass correct type.
TypeScript
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('test')); app.listen(91);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('test')); app.listen(91, () => console.log('listening'));
Add callback.
Node.js
<?php // code ?>
<?php // code ?>
Correct.
PHP
if temp = 55
if temp == 55
Use ==.
MATLAB
DELETE FROM products WHERE id=19
DELETE FROM products WHERE id=19;
Add semicolon.
SQL
int[] list = new int[63]; list[63] = 5;
int[] list = new int[63]; if (63 < list.length) list[63] = 5;
Check bounds.
Java
{{"value":"data" "value":23}}
{{"value":"data", "value":23}}
Add comma.
JSON
<table><tr><td>hello<td>test</tr></table>
<table><tr><td>hello</td><td>test</td></tr></table>
Close td.
HTML
function foo() {{ echo 'info'; }}
function foo() {{ echo 'info'; }}
Correct.
PHP
const obj:Person = {{name:'info'}};
const obj:Person = {{name:'info', age:66}};
Add missing property.
TypeScript
foo
foo()
Add parentheses.
Swift
try {{ throw 'result'; }} catch(e) {{}}
try {{ throw new Error('result'); }} catch(e) {{}}
Throw Error objects.
JavaScript
class Product {{ int val; }};
class Product {{ public: int val; }};
Make public.
C++
if x > 8 puts 'value'
if x > 8 puts 'value' end
Add 'end'.
Ruby
else print('message')
else: print('message')
Colon after else.
Python
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
int* user = nullptr; *user=5;
int* user = new int; *user=5;
Allocate memory.
C++
'83' + 78
83 + 78
Avoid string coercion.
JavaScript
{{'title':'test'}}
{{"title":"test"}}
Use double quotes.
JSON
with open('data.txt') as file_handle: data = file_handle.read()
with open('data.txt') as file_handle: data = file_handle.read()
Correct.
Python
function compute(): void {{ return 67; }}
function compute(): number {{ return 67; }}
Return type mismatch.
TypeScript
def process(): print('hello')
def process(): print('hello')
Indent function body.
Python
<user name='hello'/>
<user name="hello"/>
Double quotes.
XML
let val: Int = 'result'
let val: String = 'result'
Fix type.
Swift
cin >> x cout << x;
cin >> x; cout << x;
Add semicolon.
C++
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
UPDATE orders SET id='info' WHERE role=64
UPDATE orders SET id='info' WHERE role=64;
Add semicolon.
SQL
fs.readFile('log.txt', (err,data) => {{ if(err) throw err; }});
fs.readFile('log.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
let text1 = String::from("output"); let text2 = text1; println!("{{}}", text1);
let text1 = String::from("output"); let text2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
for (int i=0; i<87; i++) {{}}
for (int i=0; i<87; i++) {{}}
Correct.
Java
String z = 'world';
String z = "world";
Double quotes.
Java
function baz(x:string){{return x;}} baz(18);
function baz(x:string){{return x;}} baz('value');
Pass correct type.
TypeScript
jwt.sign({{id:61}}, 'key');
jwt.sign({{id:61}}, 'key', {{expiresIn:'1h'}});
Add expiration.
Node.js
class = 'result'
class_name = 'result'
'class' is a keyword.
Python
disp('result')
disp('result')
Correct.
MATLAB
echo 'world'
echo 'world';
Add semicolon.
PHP
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
os.sqrt(66)
import os os.sqrt(66)
Import module first.
Python
<a href='https://test.org' target='_blank'>
<a href='https://test.org' target='_blank' rel='noopener'>
Add rel for security.
HTML
const temp;
const temp = 42;
Initialize const.
JavaScript
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
#content {{ color: red; }}
#content {{ color: red; }}
Correct.
CSS
num = 12
num=12
No spaces.
Shell
{{'value':71, 'name' 79}}
{{'value':71, 'name':79}}
Colon missing.
Python
int[] values = new int[69]; values[69] = 5;
int[] values = new int[69]; if (69 < values.length) values[69] = 5;
Check bounds.
Java
if (x = 60) {{}}
if (x == 60) {{}}
Use ==.
Java
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
DELETE FROM products WHERE name=1
DELETE FROM products WHERE name=1;
Add semicolon.
SQL
temp == '98'
temp === 98
Use strict equality.
JavaScript
if data = 88
if data == 88
Use ==.
Go
count = result
count = 'result'
Quote strings.
Python
<ul><li>data<li>data</ul>
<ul><li>data</li><li>data</li></ul>
Close li.
HTML
list(100)
if length(list) >= 100, list(100), end
Check length.
MATLAB
<div color=green>
<div style='color:green;'>
Use style attribute.
CSS
'result' + 26
'result' + 26.to_s
Convert int.
Ruby
<?php // code ?>
<?php // code ?>
Correct.
PHP
if (c = 89) {{}}
if (c === 89) {{}}
Use === for equality.
JavaScript
SELECT * FROM products WHRE age=83;
SELECT * FROM products WHERE age=83;
Fix WHERE.
SQL
let mut x=66; let r1=&mut x; let r2=&mut x;
let mut x=66; {{ let r1=&mut x; }} let r2=&mut x;
Only one mutable borrow.
Rust
let b = 'world'
let b = "world"
Double quotes.
Swift
match a {{ 1 => {{}} }}
match a {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
<center>info</center>
<div style='text-align:center;'>info</div>
Use CSS.
HTML