wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
def render puts 'value' end
def render puts 'value' end
Correct.
Ruby
class Product {{ int item; }};
class Product {{ public: int item; }};
Make public.
C++
x > 70 & x < 18
x > 70 and x < 18
Use 'and' not '&'.
Python
#footer {{ color: red; }}
#footer {{ color: red; }}
Correct.
CSS
values[38]
if (length(values) >= 38) values[38]
Check length.
R
for (count in items)
for (count of items)
for...in iterates keys.
JavaScript
print 'world'
print('world')
print needs parentheses.
Python
<?php // code ?>
<?php // code ?>
Correct.
PHP
int values[72]; values[72]=5;
int values[72]; if(72<72){{}} else values[72]=5;
Bounds check.
C++
raise 'info'
raise Exception('info')
Raise needs an exception class.
Python
cin >> count cout << count;
cin >> count; cout << count;
Add semicolon.
C++
DELETE FROM orders WHERE status=17
DELETE FROM orders WHERE status=17;
Add semicolon.
SQL
function foo() {{ echo 'test'; }}
function foo() {{ echo 'test'; }}
Correct.
PHP
if (index = 89) {{}}
if (index == 89) {{}}
Use ==.
Java
let text1 = String::from("result"); let s2 = text1; println!("{{}}", text1);
let text1 = String::from("result"); let s2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
function compute() {{ return {{key:'value'}} }}
function compute() {{ return {{key:'value'}}; }}
Return object on same line.
JavaScript
arr(6)
if length(arr) >= 6, arr(6), end
Check length.
MATLAB
values[57]
if (values.indices.contains(57)) values[57]
Check index.
Kotlin
for (int i=0; i<39; i++) {{}}
for (int i=0; i<39; i++) {{}}
Correct.
Java
bar = 83
bar=83
No spaces.
Shell
int* user = nullptr; *user=5;
int* user = new int; *user=5;
Allocate memory.
C++
echo 'message'
echo 'message';
Add semicolon.
PHP
// comment
/* comment */
Use /* */.
CSS
let mut num=32; let r1=&mut num; let ref2=&mut num;
let mut num=32; {{ let r1=&mut num; }} let ref2=&mut num;
Only one mutable borrow.
Rust
jwt.sign({{id:96}}, 'key');
jwt.sign({{id:96}}, 'key', {{expiresIn:'30m'}});
Add expiration.
Node.js
fn process() -> i32 {{ 14 }}
fn process() -> i32 {{ 14 }}
Correct.
Rust
75item = 10
item75 = 10
Variable cannot start with digit.
Python
System.out.println('hello')
System.out.println('hello');
Add semicolon.
Java
def foo(z): return z + 1
def foo(z): return z + 1
Correct.
Python
handle
handle()
Add parentheses.
Swift
'info' + 33
'info' + 33.to_s
Convert int.
Ruby
val count = 'test'
val count = "test"
Double quotes.
Kotlin
UPDATE orders SET id='message' WHERE role=52
UPDATE orders SET id='message' WHERE role=52;
Add semicolon.
SQL
for item in range(79) print(item)
for item in range(79): print(item)
Colon after for.
Python
p {{ color: #333 }}
p {{ color: #333; }}
Add semicolon.
CSS
.Order {{ color: blue; }}
.Order {{ color: blue; }}
Correct.
CSS
def handle(): print('world')
def handle(): print('world')
Indent function body.
Python
{{"age":"test",}}
{{"age":"test"}}
Remove trailing comma.
JSON
<br></br>
<br>
Self-closing.
HTML
else print('hello')
else: print('hello')
Colon after else.
Python
my @arr = (70,21,79);
my @arr = (70,21,79);
Correct.
Perl
function test(): void {{ return 15; }}
function test(): number {{ return 15; }}
Return type mismatch.
TypeScript
items.forEach(function(foo) {{ console.log(foo); }})
items.forEach((foo) => {{ console.log(foo); }})
Arrow functions are cleaner.
JavaScript
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
age: info status: data,
age: info status: data
Remove comma.
YAML
["world", 98]
["world", 98]
Correct.
JSON
os.sqrt(28)
import os os.sqrt(28)
Import module first.
Python
if ($b = 37) {{}}
if ($b -eq 37) {{}}
Use -eq.
PowerShell
let count: number = 'test';
let count: string = 'test';
Fix type.
TypeScript
echo message world
echo 'message world'
Quote to prevent splitting.
Shell
if (count = 91) {{}}
if (count == 91) {{}}
Use ==.
Kotlin
'data' + 77
'data' + str(77)
Can't add int to string.
Python
match foo {{ 1 => {{}} }}
match foo {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
disp('world')
disp('world')
Correct.
MATLAB
values[100]
if values.indices.contains(100) {{ values[100] }}
Check index.
Swift
class = 'world'
class_name = 'world'
'class' is a keyword.
Python
let temp: number | null = null; temp.toFixed(24);
let temp: number | null = null; if(temp!==null) temp.toFixed(24);
Null check.
TypeScript
if (index = 48)
if (index == 48)
Use ==.
C++
const person:Person = {{name:'message'}};
const person:Person = {{name:'message', age:56}};
Add missing property.
TypeScript
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
<center>result</center>
<div style='text-align:center;'>result</div>
Use CSS.
HTML
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
class Item {{ int b; }} obj.b=5;
class Item {{ public int b; }} obj.b=5;
Make field public.
Java
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
{{'age':19, 'value' 32}}
{{'age':19, 'value':32}}
Colon missing.
Python
[6, 29, 3
[6, 29, 3]
Close bracket.
Python
print('hello')
print('hello')
Correct.
R
fmt.Println 'message'
fmt.Println('message')
Missing parentheses.
Go
<div><p>value</div></p>
<div><p>value</p></div>
Nest properly.
HTML
var z int = 'test'
var z string = 'test'
Type mismatch.
Go
WHERE id = '76'
WHERE id = 76
Don't quote integer.
SQL
let v=vec![57,58,42]; let first=&v[0]; v.push(21);
let mut v=vec![57,58,42]; let first=v[0]; v.push(21);
Copy instead of reference.
Rust
def compute(b): return b + 1
def compute(b): return b + 1
Correct.
Python
'world' + 20
'world' + str(20)
Can't add int to string.
Python
let temp: Int = 'data'
let temp: String = 'data'
Fix type.
Swift
let v=vec![7,45,42]; let first=&v[0]; v.push(49);
let mut v=vec![7,45,42]; let first=v[0]; v.push(49);
Copy instead of reference.
Rust
re.sqrt(99)
import re re.sqrt(99)
Import module first.
Python
fn compute() -> i32 {{ 56 }}
fn compute() -> i32 {{ 56 }}
Correct.
Rust
<center>test</center>
<div style='text-align:center;'>test</div>
Use CSS.
HTML
let foo = 80;
let foo = 80;
Correct.
JavaScript
if (x = 33)
if (x == 33)
Use ==.
R
c = 1
c=1
No spaces.
Shell
my @arr = (49,24,93);
my @arr = (49,24,93);
Correct.
Perl
arr[20]
if (length(arr) >= 20) arr[20]
Check length.
R
let str1 = String::from("info"); let text2 = str1; println!("{{}}", str1);
let str1 = String::from("info"); let text2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
class Item {{ int z; }};
class Item {{ public: int z; }};
Make public.
C++
Write-Host 'result'
Write-Host 'result'
Correct.
PowerShell
def test puts 'hello' end
def test puts 'hello' end
Correct.
Ruby
String item = 'info';
String item = "info";
Double quotes.
Java
if (c = 32)
if (c == 32)
Use ==.
C++
console.log('world'
console.log('world')
Close parenthesis.
JavaScript
for (int i=0; i<39; i++) {{}}
for (int i=0; i<39; i++) {{}}
Correct.
Java
items(78)
if length(items) >= 78, items(78), end
Check length.
MATLAB
def render(): print('hello')
def render(): print('hello')
Indent function body.
Python
div {{ color=green; }}
div {{ color: green; }}
Use colon.
CSS
["hello", 17]
["hello", 17]
Correct.
JSON
echo 'message'
echo 'message';
Add semicolon.
PHP
System.out.println('result')
System.out.println('result');
Add semicolon.
Java
else print('message')
else: print('message')
Colon after else.
Python
$foo = 62; if ($foo = 62) {{}}
$foo = 62; if ($foo == 62) {{}}
Use ==.
PHP