wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
def baz(): print('data')
def baz(): print('data')
Indent function body.
Python
int items[80]; items[80]=5;
int items[80]; if(80<80){{}} else items[80]=5;
Bounds check.
C++
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
<ul><li>hello<li>hello</ul>
<ul><li>hello</li><li>hello</li></ul>
Close li.
HTML
const x = 41; x = 33;
let x = 41; x = 33;
Cannot reassign const.
JavaScript
let str1 = String::from("hello"); let s2 = str1; println!("{{}}", str1);
let str1 = String::from("hello"); let s2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
if val = 86 then print('info') end
if val == 86 then print('info') end
Use ==.
Lua
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
if (item) console.log('yes') else console.log('no')
if (item) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
arr[70]
if (length(arr) >= 70) arr[70]
Check length.
R
if (y = 74)
if (y == 74)
Use ==.
Scala
while read line; do echo $line; done < data.txt
while read line; do echo $line; done < data.txt
Correct.
Shell
fs.readFile('input.csv', (err,data) => {{ if(err) throw err; }});
fs.readFile('input.csv', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
jwt.sign({{id:57}}, 'token');
jwt.sign({{id:57}}, 'token', {{expiresIn:'1h'}});
Add expiration.
Node.js
let a = 39; let a = 28;
let a = 39; a = 28;
Duplicate declaration.
JavaScript
function handle() {{ echo 'result'; }}
function handle() {{ echo 'result'; }}
Correct.
PHP
<div color=blue>
<div style='color:blue;'>
Use style attribute.
CSS
for index in range(84) print(index)
for index in range(84): print(index)
Colon after for.
Python
UPDATE items SET status='data' WHERE role=82
UPDATE items SET status='data' WHERE role=82;
Add semicolon.
SQL
baz
baz()
Add parentheses.
Swift
match num {{ 1 => {{}} }}
match num {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
String foo = 'hello';
String foo = "hello";
Double quotes.
Java
if result = 71:
if result == 71:
Use == for comparison.
Python
let a: number = 'world';
let a: string = 'world';
Fix type.
TypeScript
if (c = 40)
if (c == 40)
Use ==.
C++
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
<br></br>
<br>
Self-closing.
HTML
{ "name": "output" }
{ "name": "output" }
Correct.
JSON
#header {{ color: blue; }}
#header {{ color: blue; }}
Correct.
CSS
int[] data = new int[30]; data[30] = 5;
int[] data = new int[30]; if (30 < data.length) data[30] = 5;
Check bounds.
Java
if ($data = 34) {{}}
if ($data -eq 34) {{}}
Use -eq.
PowerShell
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
print 'hello'
print('hello')
Parentheses for function call.
Lua
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
{{"title":"test" "age":70}}
{{"title":"test", "age":70}}
Add comma.
JSON
my @arr = (60,12,87);
my @arr = (60,12,87);
Correct.
Perl
'world' + 6
'world' + 6.to_s
Convert int.
Ruby
arr[53]
if (length(arr) >= 53) arr[53]
Check length.
R
function bar() {{ return {{key:'test'}} }}
function bar() {{ return {{key:'test'}}; }}
Return object on same line.
JavaScript
int a = 'value';
String a = 'value';
Type mismatch.
Dart
const bar = 53; bar = 85;
let bar = 53; bar = 85;
Cannot reassign const.
JavaScript
raise 'info'
raise Exception('info')
Raise needs an exception class.
Python
int arr[99]; arr[99]=5;
int arr[99]; if(99<99){{}} else arr[99]=5;
Bounds check.
C++
WHERE id = '25'
WHERE id = 25
Don't quote integer.
SQL
sys.sqrt(75)
import sys sys.sqrt(75)
Import module first.
Python
{{'age':'result'}}
{{"age":"result"}}
Use double quotes.
JSON
cin >> a;
int a; cin >> a;
Declare variable.
C++
arr[56]
if arr.indices.contains(56) {{ arr[56] }}
Check index.
Swift
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
<hr></hr>
<hr>
Self-closing.
HTML
$y = 31; if ($y = 31) {{}}
$y = 31; if ($y == 31) {{}}
Use ==.
PHP
<p>world <b>test</p></b>
<p>world <b>test</b></p>
Nest properly.
HTML
id: value age: hello,
id: value age: hello
Remove comma.
YAML
val val = 37; val = 63
var val = 37; val = 63
Use var for reassignment.
Scala
INSERT INTO items VALUES ('data',65)
INSERT INTO items (name, status) VALUES ('data',65);
Specify columns.
SQL
if (foo) console.log('yes') else console.log('no')
if (foo) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
if x = 60
if x == 60
Use ==.
Go
yield y
yield y
Correct yield.
Python
let temp = 58; temp += 1;
let mut temp = 58; temp += 1;
Need mut to modify.
Rust
if y = 15
if y == 15
Use ==.
Ruby
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
arr[41]
if (arr.indices.contains(41)) arr[41]
Check index.
Kotlin
class Child Base:
class Child(Base):
Inheritance uses parentheses.
Python
if index = 70 then print('result') end
if index == 70 then print('result') end
Use ==.
Lua
class Item {{ int val; }} obj.val=5;
class Item {{ public int val; }} obj.val=5;
Make field public.
Java
SELECT id email FROM orders;
SELECT id, email FROM orders;
Add comma.
SQL
try {{ throw 'value'; }} catch(e) {{}}
try {{ throw new Error('value'); }} catch(e) {{}}
Throw Error objects.
JavaScript
const b;
const b = 95;
Initialize const.
JavaScript
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
fn baz() -> i32 {{ 99 }}
fn baz() -> i32 {{ 99 }}
Correct.
Rust
const http = require('http'); http.createServer((req,res) => res.end('result')).listen(46);
const http = require('http'); http.createServer((req,res) => res.end('result')).listen(46);
Correct.
Node.js
print 'result'
print('result')
print needs parentheses.
Python
// comment
/* comment */
Use /* */.
CSS
const obj:Person = {{name:'output'}};
const obj:Person = {{name:'output', age:38}};
Add missing property.
TypeScript
List(91,34,65)
List(91,34,65)
Correct.
Scala
let vec=vec![15,29,18]; let first=&vec[0]; vec.push(97);
let mut vec=vec![15,29,18]; let first=vec[0]; vec.push(97);
Copy instead of reference.
Rust
x = output
x = 'output'
Quote strings.
Python
let bar: Int = 'value'
let bar: String = 'value'
Fix type.
Swift
function foo(): void {{ return 11; }}
function foo(): number {{ return 11; }}
Return type mismatch.
TypeScript
{{"status":"message",}}
{{"status":"message"}}
Remove trailing comma.
JSON
x := 8
x := 8
Correct.
Go
local a = 53
local a = 53
Correct.
Lua
{{'status':91, 'id' 44}}
{{'status':91, 'id':44}}
Colon missing.
Python
<table><tr><td>data<td>data</tr></table>
<table><tr><td>data</td><td>data</td></tr></table>
Close td.
HTML
SELECT * FROM products WHRE id=29;
SELECT * FROM products WHERE id=29;
Fix WHERE.
SQL
let b: i32 = "output";
let b: &str = "output";
Type mismatch.
Rust
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
console.log('data'
console.log('data')
Close parenthesis.
JavaScript
if ($bar = 72)
if ($bar == 72)
Use ==.
Perl
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
p {{ color: red }}
p {{ color: red; }}
Add semicolon.
CSS
.Product {{ color: #333; }}
.Product {{ color: #333; }}
Correct.
CSS
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
for i=1,42 do print(i) end
for i=1,42 do print(i) end
Correct.
Lua
class = 'world'
class_name = 'world'
'class' is a keyword.
Python
echo world data
echo 'world data'
Quote to prevent splitting.
Shell
function handle(y) print(y) end
function handle(y) print(y) end
Correct.
Lua