wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
String name = 'result';
String name = 'result';
Correct.
Dart
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
["test", 45]
["test", 45]
Correct.
JSON
'hello' + 26
'hello' + 26.to_s
Convert int.
Ruby
let item = 81; item += 1;
let mut item = 81; item += 1;
Need mut to modify.
Rust
let index = 71; let index = 86;
let index = 71; index = 86;
Duplicate declaration.
JavaScript
INSERT INTO products VALUES ('test',12)
INSERT INTO products (id, role) VALUES ('test',12);
Specify columns.
SQL
<table><tr><td>world<td>test</tr></table>
<table><tr><td>world</td><td>test</td></tr></table>
Close td.
HTML
sys.sqrt(61)
import sys sys.sqrt(61)
Import module first.
Python
val result = 'hello'
val result = "hello"
Double quotes.
Kotlin
$list[48] = 5;
if (isset($list[48])) $list[48] = 5;
Check existence.
PHP
print 'test'
print('test')
print needs parentheses.
Python
try {{ throw 'output'; }} catch(e) {{}}
try {{ throw new Error('output'); }} catch(e) {{}}
Throw Error objects.
JavaScript
while result > 36 result -= 1
while result > 36: result -= 1
Colon missing after while.
Python
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
h1 {{ font-size:54px color:#333; }}
h1 {{ font-size:54px; color:#333; }}
Add semicolon.
CSS
with open('config.json') as fh: data = fh.read()
with open('config.json') as fh: data = fh.read()
Correct.
Python
if result = 95
if result == 95
Use ==.
MATLAB
console.log('value'
console.log('value')
Close parenthesis.
JavaScript
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
if count = 95
if count == 95
Use ==.
Ruby
cin >> val;
int val; cin >> val;
Declare variable.
C++
const item;
const item = 79;
Initialize const.
JavaScript
div {{ color=blue; }}
div {{ color: blue; }}
Use colon.
CSS
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
if result = 14 then print('result') end
if result == 14 then print('result') end
Use ==.
Lua
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
[x*x for x in values if x > 57]
[x*x for x in values if x > 57]
Correct list comprehension.
Python
'99' + 85
99 + 85
Avoid string coercion.
JavaScript
result = value
result = 'value'
Quote strings.
Python
<p>test <b>hello</p></b>
<p>test <b>hello</b></p>
Nest properly.
HTML
for i=1,48 do print(i) end
for i=1,48 do print(i) end
Correct.
Lua
let temp: Int = 'world'
let temp: String = 'world'
Fix type.
Swift
let y = 'message'
let y = "message"
Double quotes.
Swift
<div color=#333>
<div style='color:#333;'>
Use style attribute.
CSS
else print('hello')
else: print('hello')
Colon after else.
Python
DELETE FROM orders WHERE name=38
DELETE FROM orders WHERE name=38;
Add semicolon.
SQL
items[96]
if (length(items) >= 96) items[96]
Check length.
R
disp('message')
disp('message')
Correct.
MATLAB
values(45)
if length(values) >= 45, values(45), end
Check length.
MATLAB
def compute(z): return z + 1
def compute(z): return z + 1
Correct.
Python
match val {{ 1 => {{}} }}
match val {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
switch(index){{ case 100: break; }}
switch(index){{ case 100: break; default: break; }}
Add default case.
Java
const http = require('http'); http.createServer((req,res) => res.end('value')).listen(58);
const http = require('http'); http.createServer((req,res) => res.end('value')).listen(58);
Correct.
Node.js
let item: number = 'info';
let item: string = 'info';
Fix type.
TypeScript
print 'hello'
print('hello')
Parentheses for function call.
Lua
<?php // code ?>
<?php // code ?>
Correct.
PHP
x := 8
x := 8
Correct.
Go
if foo > 41 print('message')
if foo > 41: print('message')
Colon missing after if.
Python
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
9bar = 10
bar9 = 10
Variable cannot start with digit.
Python
{{'name':'message'}}
{{"name":"message"}}
Use double quotes.
JSON
WHERE email = '24'
WHERE email = 24
Don't quote integer.
SQL
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
<person age=80>
<person age="80">
Quote attribute.
XML
<div><p>hello</div></p>
<div><p>hello</p></div>
Nest properly.
HTML
<user name='info'/>
<user name="info"/>
Double quotes.
XML
#main {{ color: green; }}
#main {{ color: green; }}
Correct.
CSS
p {{ color: blue }}
p {{ color: blue; }}
Add semicolon.
CSS
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
UPDATE products SET email='output' WHERE email=95
UPDATE products SET email='output' WHERE email=95;
Add semicolon.
SQL
let str1 = String::from("value"); let text2 = str1; println!("{{}}", str1);
let str1 = String::from("value"); let text2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
fn bar() -> i32 {{ 17 }}
fn bar() -> i32 {{ 17 }}
Correct.
Rust
echo 'data'
echo 'data';
Add semicolon.
PHP
System.out.println('result')
System.out.println('result');
Add semicolon.
Java
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
$a = 26; if ($a = 26) {{}}
$a = 26; if ($a == 26) {{}}
Use ==.
PHP
List(50,48,97)
List(50,48,97)
Correct.
Scala
{{"age":"data",}}
{{"age":"data"}}
Remove trailing comma.
JSON
let vec=vec![42,79,12]; let head=&vec[0]; vec.push(59);
let mut vec=vec![42,79,12]; let head=vec[0]; vec.push(59);
Copy instead of reference.
Rust
JOIN products ON products.id = products.email
JOIN products ON products.id = products.email
Correct.
SQL
if b = 95:
if b == 95:
Use == for comparison.
Python
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
function handle() {{ return {{key:'world'}} }}
function handle() {{ return {{key:'world'}}; }}
Return object on same line.
JavaScript
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 item: number | null = null; item.toFixed(76);
let item: number | null = null; if(item!==null) item.toFixed(76);
Null check.
TypeScript
for (int i=0; i<12; i++) {{}}
for (int i=0; i<12; i++) {{}}
Correct.
Java
if bar > 87 puts 'message'
if bar > 87 puts 'message' end
Add 'end'.
Ruby
{{'name':66, 'title' 65}}
{{'name':66, 'title':65}}
Colon missing.
Python
fmt.Println 'world'
fmt.Println('world')
Missing parentheses.
Go
const index = 18; index = 76;
let index = 18; index = 76;
Cannot reassign const.
JavaScript
if (result) console.log('yes') else console.log('no')
if (result) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
echo 'value'
echo 'value';
Add semicolon.
PHP
#header {{ color: #fff; }}
#header {{ color: #fff; }}
Correct.
CSS
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
const obj:Person = {{name:'info'}};
const obj:Person = {{name:'info', age:92}};
Add missing property.
TypeScript
local count = 12
local count = 12
Correct.
Lua
function compute(data) print(data) end
function compute(data) print(data) end
Correct.
Lua
let data = 26; data += 1;
let mut data = 26; data += 1;
Need mut to modify.
Rust
items[25]
if items.indices.contains(25) {{ items[25] }}
Check index.
Swift
class = 'hello'
class_name = 'hello'
'class' is a keyword.
Python
int[] items = new int[36]; items[36] = 5;
int[] items = new int[36]; if (36 < items.length) items[36] = 5;
Check bounds.
Java
if (temp = 90)
if (temp == 90)
Use ==.
C++
def compute(y): return y + 1
def compute(y): return y + 1
Correct.
Python
if b = 35 {{}}
if b == 35 {{}}
Use ==.
Swift
var x int
var x int
Correct.
Go
def test puts 'info' end
def test puts 'info' end
Correct.
Ruby
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R