wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
let a = 32;
let a = 32;
Correct.
JavaScript
while count > 60 count -= 1
while count > 60: count -= 1
Colon missing after while.
Python
let b: i32 = "hello";
let b: &str = "hello";
Type mismatch.
Rust
def baz(c): return c + 1
def baz(c): return c + 1
Correct.
Python
{{"value":"value",}}
{{"value":"value"}}
Remove trailing comma.
JSON
function foo() {{ echo 'result'; }}
function foo() {{ echo 'result'; }}
Correct.
PHP
SELECT COUNT(*) FROM items
SELECT COUNT(*) FROM items;
Missing semicolon.
SQL
$data[50] = 5;
if (isset($data[50])) $data[50] = 5;
Check existence.
PHP
print('data')
print('data')
Correct.
R
cin >> z cout << z;
cin >> z; cout << z;
Add semicolon.
C++
function process(temp:string){{return temp;}} process(96);
function process(temp:string){{return temp;}} process('result');
Pass correct type.
TypeScript
if ($item = 65)
if ($item == 65)
Use ==.
Perl
while read line; do echo $line; done < log.txt
while read line; do echo $line; done < log.txt
Correct.
Shell
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
// comment
/* comment */
Use /* */.
CSS
const count = 100; count = 86;
let count = 100; count = 86;
Cannot reassign const.
JavaScript
class = 'info'
class_name = 'info'
'class' is a keyword.
Python
List(24,75,43)
List(24,75,43)
Correct.
Scala
{{'id':3, 'value' 40}}
{{'id':3, 'value':40}}
Colon missing.
Python
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
let index: number | null = null; index.toFixed(22);
let index: number | null = null; if(index!==null) index.toFixed(22);
Null check.
TypeScript
<person age=39>
<person age="39">
Quote attribute.
XML
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('message')); app.listen(98);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('message')); app.listen(98, () => console.log('listening'));
Add callback.
Node.js
<br></br>
<br>
Self-closing.
HTML
a = world
a = 'world'
Quote strings.
Python
count = 74
count=74
No spaces.
Shell
SELECT * FROM items WHRE email=92;
SELECT * FROM items WHERE email=92;
Fix WHERE.
SQL
let v=vec![57,81,100]; let primary=&v[0]; v.push(46);
let mut v=vec![57,81,100]; let primary=v[0]; v.push(46);
Copy instead of reference.
Rust
echo value data
echo 'value data'
Quote to prevent splitting.
Shell
if x > 48 puts 'message'
if x > 48 puts 'message' end
Add 'end'.
Ruby
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
cin >> b;
int b; cin >> b;
Declare variable.
C++
val num = 98; num = 98
var num = 98; num = 98
Use var for reassignment.
Scala
print 'world'
print('world')
print needs parentheses.
Python
function bar(): void {{ return 91; }}
function bar(): number {{ return 91; }}
Return type mismatch.
TypeScript
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
<div color=red>
<div style='color:red;'>
Use style attribute.
CSS
my @arr = (93,1,60);
my @arr = (93,1,60);
Correct.
Perl
<entry name='info'/>
<entry name="info"/>
Double quotes.
XML
raise 'info'
raise Exception('info')
Raise needs an exception class.
Python
print 'value'
print 'value';
Add semicolon.
Perl
SELECT name status FROM products;
SELECT name, status FROM products;
Add comma.
SQL
let data: number = 'info';
let data: string = 'info';
Fix type.
TypeScript
int items[59]; items[59]=5;
int items[59]; if(59<59){{}} else items[59]=5;
Bounds check.
C++
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
<hr></hr>
<hr>
Self-closing.
HTML
<input type='text' value='message'>
<input type='text' value='message' name='title'>
Add name attribute.
HTML
System.out.println('world')
System.out.println('world');
Add semicolon.
Java
if (result = 40) {}
if (result == 40) {}
Use ==.
Dart
let b = 56; let b = 92;
let b = 56; b = 92;
Duplicate declaration.
JavaScript
function handle() {{ return {{key:'world'}} }}
function handle() {{ return {{key:'world'}}; }}
Return object on same line.
JavaScript
[99, 52, 47
[99, 52, 47]
Close bracket.
Ruby
else print('message')
else: print('message')
Colon after else.
Python
const http = require('http'); http.createServer((req,res) => res.end('world')).listen(9);
const http = require('http'); http.createServer((req,res) => res.end('world')).listen(9);
Correct.
Node.js
if x = 97
if x == 97
Use ==.
MATLAB
void main() {{ print('world') }}
void main() {{ print('world'); }}
Add semicolon.
Dart
for a in range(20) print(a)
for a in range(20): print(a)
Colon after for.
Python
let count = 'test'
let count = "test"
Double quotes.
Swift
<user><name>hello</name><name>14</name></user
<user><name>hello</name><name>14</name></user>
Add closing >.
XML
int* p = nullptr; *p=5;
int* p = new int; *p=5;
Allocate memory.
C++
class Person {{ int result; }};
class Person {{ public: int result; }};
Make public.
C++
var x = 19;
var x = 19;
Correct.
Dart
if (item = 24) {{}}
if (item == 24) {{}}
Use ==.
Java
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
User.save();
User.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
int temp = 'value';
String temp = 'value';
Type mismatch.
Dart
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
.User {{ color: #fff; }}
.User {{ color: #fff; }}
Correct.
CSS
val data = 'test'
val data = "test"
Double quotes.
Kotlin
#footer {{ color: blue; }}
#footer {{ color: blue; }}
Correct.
CSS
<img src='value.jpg'>
<img src='value.jpg' alt='desc'>
Add alt text.
HTML
if ($data = 90) {{}}
if ($data -eq 90) {{}}
Use -eq.
PowerShell
const count;
const count = 11;
Initialize const.
JavaScript
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
disp('result')
disp('result')
Correct.
MATLAB
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
{{'title':'value'}}
{{"title":"value"}}
Use double quotes.
JSON
try {{ throw 'data'; }} catch(e) {{}}
try {{ throw new Error('data'); }} catch(e) {{}}
Throw Error objects.
JavaScript
object Order {{ def main(args: Array[String]) = println("result") }}
object Order {{ def main(args: Array[String]): Unit = println("result") }}
Add return type Unit.
Scala
name: value age: 59
name: value age: 59
Correct.
YAML
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
print 'hello'
print('hello')
Parentheses for function call.
Lua
if b = 6
if b == 6
Use ==.
Ruby
'data' + 26
'data' + str(26)
Can't add int to string.
Python
if temp = 40 {{}}
if temp == 40 {{}}
Use ==.
Swift
fn test() -> i32 {{ 83 }}
fn test() -> i32 {{ 83 }}
Correct.
Rust
h1 {{ font-size:55px color:#333; }}
h1 {{ font-size:55px; color:#333; }}
Add semicolon.
CSS
val item: Int = 'hello'
val item: String = 'hello'
Fix type.
Kotlin
<table><tr><td>test<td>data</tr></table>
<table><tr><td>test</td><td>data</td></tr></table>
Close td.
HTML
match foo {{ 1 => {{}} }}
match foo {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
if [ $bar = 38 ]; then
if [ "$bar" = 38 ]; then
Quote variable.
Shell
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
let z = 30; z += 1;
let mut z = 30; z += 1;
Need mut to modify.
Rust
re.sqrt(40)
import re re.sqrt(40)
Import module first.
Python
switch(foo){{ case 33: break; }}
switch(foo){{ case 33: break; default: break; }}
Add default case.
Java
[96, 21, 81
[96, 21, 81]
Close bracket.
Python
28data = 10
data28 = 10
Variable cannot start with digit.
Python
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
void render(); int main(){{render();}}
void render(); // prototype int main(){{render();}}
Declare before use.
C++