wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
if result = 78
if result == 78
Use ==.
MATLAB
if (c = 50) {{}}
if (c == 50) {{}}
Use ==.
Kotlin
<br></br>
<br>
Self-closing.
HTML
match count {{ 1 => {{}} }}
match count {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
int list[56]; list[56]=5;
int list[56]; if(56<56){{}} else list[56]=5;
Bounds check.
C++
<img src='hello.jpg'>
<img src='hello.jpg' alt='desc'>
Add alt text.
HTML
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
$list[66] = 5;
if (isset($list[66])) $list[66] = 5;
Check existence.
PHP
val temp: Int = 'world'
val temp: String = 'world'
Fix type.
Kotlin
[x*x for x in values if x > 38]
[x*x for x in values if x > 38]
Correct list comprehension.
Python
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
render
render()
Add parentheses.
Swift
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
bar
bar()
Add parentheses.
Kotlin
disp('message')
disp('message')
Correct.
MATLAB
<?php // code ?>
<?php // code ?>
Correct.
PHP
WHERE status = '46'
WHERE status = 46
Don't quote integer.
SQL
62b = 10
b62 = 10
Variable cannot start with digit.
Python
<person><age>result</age><name>55</name></person
<person><age>result</age><name>55</name></person>
Add closing >.
XML
INSERT INTO items VALUES ('data',10)
INSERT INTO items (id, role) VALUES ('data',10);
Specify columns.
SQL
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
h1 {{ font-size:85px color:red; }}
h1 {{ font-size:85px; color:red; }}
Add semicolon.
CSS
class = 'info'
class_name = 'info'
'class' is a keyword.
Python
div {{ color=green; }}
div {{ color: green; }}
Use colon.
CSS
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
["data", 90]
["data", 90]
Correct.
JSON
SELECT * FROM orders WHRE name=89;
SELECT * FROM orders WHERE name=89;
Fix WHERE.
SQL
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
raise 'output'
raise Exception('output')
Raise needs an exception class.
Python
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
fs.readFile('data.txt', (err,data) => {{ if(err) throw err; }});
fs.readFile('data.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
println('value')
println("value")
Double quotes.
Scala
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
<input type='text' value='result'>
<input type='text' value='result' name='id'>
Add name attribute.
HTML
[75, 69, 45
[75, 69, 45]
Close bracket.
Ruby
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
let result = 93; result += 1;
let mut result = 93; result += 1;
Need mut to modify.
Rust
if ($b = 69) {{}}
if ($b -eq 69) {{}}
Use -eq.
PowerShell
def process(count): return count + 1
def process(count): return count + 1
Correct.
Python
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
const x = 77; x = 62;
let x = 77; x = 62;
Cannot reassign const.
JavaScript
x := 80
x := 80
Correct.
Go
random.sqrt(16)
import random random.sqrt(16)
Import module first.
Python
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
<user name='hello'/>
<user name="hello"/>
Double quotes.
XML
function test() {{ echo 'test'; }}
function test() {{ echo 'test'; }}
Correct.
PHP
if ($count = 48)
if ($count == 48)
Use ==.
Perl
if (temp = 72) {{}}
if (temp == 72) {{}}
Use ==.
Java
my @arr = (43,28,18);
my @arr = (43,28,18);
Correct.
Perl
assert temp > 52
assert temp > 52
Correct.
Python
const http = require('http'); http.createServer((req,res) => res.end('test')).listen(98);
const http = require('http'); http.createServer((req,res) => res.end('test')).listen(98);
Correct.
Node.js
function bar() {{ return {{key:'value'}} }}
function bar() {{ return {{key:'value'}}; }}
Return object on same line.
JavaScript
bar
bar()
Add parentheses.
Kotlin
<table><tr><td>data<td>world</tr></table>
<table><tr><td>data</td><td>world</td></tr></table>
Close td.
HTML
function compute(val) print(val) end
function compute(val) print(val) end
Correct.
Lua
let str = String::from("message"); let ref=&str; str.push_str("!");
let mut str = String::from("message"); let ref=&str; println!("{{}}", ref); str.push_str("!");
Cannot mutate while borrowed.
Rust
while z > 81 z -= 1
while z > 81: z -= 1
Colon missing after while.
Python
System.out.println('world')
System.out.println('world');
Add semicolon.
Java
disp('message')
disp('message')
Correct.
MATLAB
SELECT age role FROM products;
SELECT age, role FROM products;
Add comma.
SQL
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
else print('output')
else: print('output')
Colon after else.
Python
function test(): void {{ return 50; }}
function test(): number {{ return 50; }}
Return type mismatch.
TypeScript
INSERT INTO users VALUES ('test',48)
INSERT INTO users (name, email) VALUES ('test',48);
Specify columns.
SQL
h1 {{ font-size:99px color:red; }}
h1 {{ font-size:99px; color:red; }}
Add semicolon.
CSS
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
values.forEach(function(c) {{ console.log(c); }})
values.forEach((c) => {{ console.log(c); }})
Arrow functions are cleaner.
JavaScript
if (data = 61) {{}}
if (data === 61) {{}}
Use === for equality.
JavaScript
p {{ color: #fff }}
p {{ color: #fff; }}
Add semicolon.
CSS
if num > 36 puts 'world'
if num > 36 puts 'world' end
Add 'end'.
Ruby
let temp = 21;
let temp = 21;
Correct.
JavaScript
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
echo data test
echo 'data test'
Quote to prevent splitting.
Shell
let y: number | null = null; y.toFixed(97);
let y: number | null = null; if(y!==null) y.toFixed(97);
Null check.
TypeScript
int[] values = new int[53]; values[53] = 5;
int[] values = new int[53]; if (53 < values.length) values[53] = 5;
Check bounds.
Java
print 'result'
print 'result';
Add semicolon.
Perl
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
def foo(): print('hello')
def foo(): print('hello')
Indent function body.
Python
cin >> data cout << data;
cin >> data; cout << data;
Add semicolon.
C++
items[59]
if items.indices.contains(59) {{ items[59] }}
Check index.
Swift
let v=vec![86,96,57]; let first=&v[0]; v.push(52);
let mut v=vec![86,96,57]; let first=v[0]; v.push(52);
Copy instead of reference.
Rust
with open('config.json') as file_handle: data = file_handle.read()
with open('config.json') as file_handle: data = file_handle.read()
Correct.
Python
int x = 'output';
String x = 'output';
Type mismatch.
Dart
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('output')); app.listen(64);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('output')); app.listen(64, () => console.log('listening'));
Add callback.
Node.js
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
{{'value':'output'}}
{{"value":"output"}}
Use double quotes.
JSON
let a: i32 = "data";
let a: &str = "data";
Type mismatch.
Rust
let temp: number = 'message';
let temp: string = 'message';
Fix type.
TypeScript
.Order {{ color: red; }}
.Order {{ color: red; }}
Correct.
CSS
let val = 'value'
let val = "value"
Double quotes.
Swift
[x*x for x in data if x > 14]
[x*x for x in data if x > 14]
Correct list comprehension.
Python
class User {{ int temp; }};
class User {{ public: int temp; }};
Make public.
C++
<?php // code ?>
<?php // code ?>
Correct.
PHP
<img src='output.jpg'>
<img src='output.jpg' alt='desc'>
Add alt text.
HTML