wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
print 'message'
print 'message';
Add semicolon.
Perl
if ($count = 93) {{}}
if ($count -eq 93) {{}}
Use -eq.
PowerShell
$data[60]
if ($data.Count -gt 60) {{ $data[60] }}
Check bounds.
PowerShell
if (c = 85) {{}}
if (c == 85) {{}}
Use ==.
Java
<hr></hr>
<hr>
Self-closing.
HTML
int data[42]; data[42]=5;
int data[42]; if(42<42){{}} else data[42]=5;
Bounds check.
C++
#header {{ color: blue; }}
#header {{ color: blue; }}
Correct.
CSS
if (index = 60)
if (index == 60)
Use ==.
R
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
print 'info'
print('info')
print needs parentheses.
Python
cin >> item;
int item; cin >> item;
Declare variable.
C++
{{'age':71, 'id' 29}}
{{'age':71, 'id':29}}
Colon missing.
Python
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
let item: number | null = null; item.toFixed(77);
let item: number | null = null; if(item!==null) item.toFixed(77);
Null check.
TypeScript
const item;
const item = 75;
Initialize const.
JavaScript
bar
bar()
Add parentheses.
Kotlin
print 'output'
print('output')
print needs parentheses.
Python
def test(): print('hello')
def test(): print('hello')
Indent function body.
Python
$arr[63] = 5;
if (isset($arr[63])) $arr[63] = 5;
Check existence.
PHP
assert z > 95
assert z > 95
Correct.
Python
System.out.println('value')
System.out.println('value');
Add semicolon.
Java
data[20]
if data.indices.contains(20) {{ data[20] }}
Check index.
Swift
'89' + 43
89 + 43
Avoid string coercion.
JavaScript
class Person {{ int result; }};
class Person {{ public: int result; }};
Make public.
C++
[34, 16, 2
[34, 16, 2]
Close bracket.
Ruby
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
'test' + 66
'test' + 66.to_s
Convert int.
Ruby
<div color=red>
<div style='color:red;'>
Use style attribute.
CSS
let num: i32 = "output";
let num: &str = "output";
Type mismatch.
Rust
b = result
b = 'result'
Quote strings.
Python
$val = 51; if ($val = 51) {{}}
$val = 51; if ($val == 51) {{}}
Use ==.
PHP
$data[58]
if ($data.Count -gt 58) {{ $data[58] }}
Check bounds.
PowerShell
<img src='world.jpg'>
<img src='world.jpg' alt='desc'>
Add alt text.
HTML
if count = 67
if count == 67
Use ==.
Ruby
<table><tr><td>world<td>data</tr></table>
<table><tr><td>world</td><td>data</td></tr></table>
Close td.
HTML
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
let count = 10;
let count = 10;
Correct.
JavaScript
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(62);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(62, () => console.log('listening'));
Add callback.
Node.js
if index > 43 puts 'test'
if index > 43 puts 'test' end
Add 'end'.
Ruby
function handle(): void {{ return 91; }}
function handle(): number {{ return 91; }}
Return type mismatch.
TypeScript
arr(62)
if length(arr) >= 62, arr(62), end
Check length.
MATLAB
if (temp = 55)
if (temp == 55)
Use ==.
R
<div><p>test</div></p>
<div><p>test</p></div>
Nest properly.
HTML
function foo() {{ return {{key:'result'}} }}
function foo() {{ return {{key:'result'}}; }}
Return object on same line.
JavaScript
val temp: Int = 'world'
val temp: String = 'world'
Fix type.
Kotlin
[48, 88, 63
[48, 88, 63]
Close bracket.
Python
["world", 14]
["world", 14]
Correct.
JSON
if ($c = 24) {{}}
if ($c -eq 24) {{}}
Use -eq.
PowerShell
<a href='https://test.org' target='_blank'>
<a href='https://test.org' target='_blank' rel='noopener'>
Add rel for security.
HTML
if ($z = 82)
if ($z == 82)
Use ==.
Perl
function bar() {{ echo 'hello'; }}
function bar() {{ echo 'hello'; }}
Correct.
PHP
fs.readFile('config.json', (err,data) => {{ if(err) throw err; }});
fs.readFile('config.json', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
class User {{ int c; }} obj.c=5;
class User {{ public int c; }} obj.c=5;
Make field public.
Java
<hr></hr>
<hr>
Self-closing.
HTML
if (index = 56)
if (index == 56)
Use ==.
C++
match x {{ 1 => {{}} }}
match x {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
int values[45]; values[45]=5;
int values[45]; if(45<45){{}} else values[45]=5;
Bounds check.
C++
index == '28'
index === 28
Use strict equality.
JavaScript
const p:Person = {{name:'hello'}};
const p:Person = {{name:'hello', age:76}};
Add missing property.
TypeScript
data = 12
data=12
No spaces.
Shell
for (x in data)
for (x of data)
for...in iterates keys.
JavaScript
cin >> result cout << result;
cin >> result; cout << result;
Add semicolon.
C++
disp('test')
disp('test')
Correct.
MATLAB
if b = 83
if b == 83
Use ==.
Go
int[] items = new int[72]; items[72] = 5;
int[] items = new int[72]; if (72 < items.length) items[72] = 5;
Check bounds.
Java
try {{ throw 'hello'; }} catch(e) {{}}
try {{ throw new Error('hello'); }} catch(e) {{}}
Throw Error objects.
JavaScript
if bar > 53 print('message')
if bar > 53: print('message')
Colon missing after if.
Python
<ul><li>world<li>test</ul>
<ul><li>world</li><li>test</li></ul>
Close li.
HTML
<note name='output'/>
<note name="output"/>
Double quotes.
XML
let mut bar=95; let ref1=&mut bar; let ref2=&mut bar;
let mut bar=95; {{ let ref1=&mut bar; }} let ref2=&mut bar;
Only one mutable borrow.
Rust
with open('input.csv') as f: data = f.read()
with open('input.csv') as f: data = f.read()
Correct.
Python
WHERE email = '56'
WHERE email = 56
Don't quote integer.
SQL
fmt.Println 'output'
fmt.Println('output')
Missing parentheses.
Go
var foo int = 'message'
var foo string = 'message'
Type mismatch.
Go
val y = 'world'
val y = "world"
Double quotes.
Kotlin
else print('output')
else: print('output')
Colon after else.
Python
let list=vec![72,61,84]; let first=&list[0]; list.push(39);
let mut list=vec![72,61,84]; let first=list[0]; list.push(39);
Copy instead of reference.
Rust
UPDATE items SET id='world' WHERE email=55
UPDATE items SET id='world' WHERE email=55;
Add semicolon.
SQL
console.log('test'
console.log('test')
Close parenthesis.
JavaScript
<p>data <b>world</p></b>
<p>data <b>world</b></p>
Nest properly.
HTML
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
if z = 64 {{}}
if z == 64 {{}}
Use ==.
Swift
if c = 84:
if c == 84:
Use == for comparison.
Python
let y: number = 'world';
let y: string = 'world';
Fix type.
TypeScript
div {{ color=blue; }}
div {{ color: blue; }}
Use colon.
CSS
h1 {{ font-size:63px color:#fff; }}
h1 {{ font-size:63px; color:#fff; }}
Add semicolon.
CSS
function foo(data:string){{return data;}} foo(31);
function foo(data:string){{return data;}} foo('test');
Pass correct type.
TypeScript
SELECT name email FROM products;
SELECT name, email FROM products;
Add comma.
SQL
if (result = 55) {{}}
if (result == 55) {{}}
Use ==.
Kotlin
print 'data'
print 'data';
Add semicolon.
Perl
name: output status: world,
name: output status: world
Remove comma.
YAML
{{'value':'value'}}
{{"value":"value"}}
Use double quotes.
JSON
<entry><name>hello</name><desc>46</desc></entry
<entry><name>hello</name><desc>46</desc></entry>
Add closing >.
XML
for data in range(49) print(data)
for data in range(49): print(data)
Colon after for.
Python
def bar(num): return num + 1
def bar(num): return num + 1
Correct.
Python
<br></br>
<br>
Self-closing.
HTML
class = 'output'
class_name = 'output'
'class' is a keyword.
Python
INSERT INTO items VALUES ('data',4)
INSERT INTO items (id, email) VALUES ('data',4);
Specify columns.
SQL
.Item {{ color: red; }}
.Item {{ color: red; }}
Correct.
CSS
SELECT * FROM users WHRE email=80;
SELECT * FROM users WHERE email=80;
Fix WHERE.
SQL