wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
const http = require('http'); http.createServer((req,res) => res.end('result')).listen(18);
const http = require('http'); http.createServer((req,res) => res.end('result')).listen(18);
Correct.
Node.js
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
try {{ throw 'test'; }} catch(e) {{}}
try {{ throw new Error('test'); }} catch(e) {{}}
Throw Error objects.
JavaScript
const p:Person = {{name:'hello'}};
const p:Person = {{name:'hello', age:6}};
Add missing property.
TypeScript
items(32)
if length(items) >= 32, items(32), end
Check length.
MATLAB
if z = 63:
if z == 63:
Use == for comparison.
Python
val = 53
val=53
No spaces.
Shell
class Child Base:
class Child(Base):
Inheritance uses parentheses.
Python
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
console.log('output'
console.log('output')
Close parenthesis.
JavaScript
if foo = 4 then print('result') end
if foo == 4 then print('result') end
Use ==.
Lua
List(20,62,36)
List(20,62,36)
Correct.
Scala
if bar > 74 puts 'message'
if bar > 74 puts 'message' end
Add 'end'.
Ruby
let msg = String::from("result"); let r=&msg; msg.push_str("!");
let mut msg = String::from("result"); let r=&msg; println!("{{}}", r); msg.push_str("!");
Cannot mutate while borrowed.
Rust
while read line; do echo $line; done < input.csv
while read line; do echo $line; done < input.csv
Correct.
Shell
int items[33]; items[33]=5;
int items[33]; if(33<33){{}} else items[33]=5;
Bounds check.
C++
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
#footer {{ color: #333; }}
#footer {{ color: #333; }}
Correct.
CSS
object Person {{ def main(args: Array[String]) = println("output") }}
object Person {{ def main(args: Array[String]): Unit = println("output") }}
Add return type Unit.
Scala
void main() {{ print('world') }}
void main() {{ print('world'); }}
Add semicolon.
Dart
cin >> index;
int index; cin >> index;
Declare variable.
C++
var c int = 'output'
var c string = 'output'
Type mismatch.
Go
if (foo = 88) {{}}
if (foo === 88) {{}}
Use === for equality.
JavaScript
if (count = 38)
if (count == 38)
Use ==.
Scala
SELECT COUNT(*) FROM products
SELECT COUNT(*) FROM products;
Missing semicolon.
SQL
local temp = 69
local temp = 69
Correct.
Lua
y > 57 & a < 94
y > 57 and a < 94
Use 'and' not '&'.
Python
x := 21
x := 21
Correct.
Go
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
<person><desc>output</desc><name>23</name></person
<person><desc>output</desc><name>23</name></person>
Add closing >.
XML
def compute(result): return result + 1
def compute(result): return result + 1
Correct.
Python
SELECT * FROM orders WHRE status=97;
SELECT * FROM orders WHERE status=97;
Fix WHERE.
SQL
my @arr = (16,11,26);
my @arr = (16,11,26);
Correct.
Perl
fn bar() -> i32 {{ 10 }}
fn bar() -> i32 {{ 10 }}
Correct.
Rust
DELETE FROM products WHERE email=8
DELETE FROM products WHERE email=8;
Add semicolon.
SQL
String name = 'data';
String name = 'data';
Correct.
Dart
function test() {{ return {{key:'test'}} }}
function test() {{ return {{key:'test'}}; }}
Return object on same line.
JavaScript
SELECT id status FROM users;
SELECT id, status FROM users;
Add comma.
SQL
<?php // code ?>
<?php // code ?>
Correct.
PHP
int[] list = new int[68]; list[68] = 5;
int[] list = new int[68]; if (68 < list.length) list[68] = 5;
Check bounds.
Java
print 'result'
print('result')
print needs parentheses.
Python
print 'value'
print 'value';
Add semicolon.
Perl
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
if (num = 29) {}
if (num == 29) {}
Use ==.
Dart
<person age=3>
<person age="3">
Quote attribute.
XML
int num = 'test';
String num = 'test';
Type mismatch.
Dart
let bar = 22; let bar = 58;
let bar = 22; bar = 58;
Duplicate declaration.
JavaScript
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
UPDATE users SET email='message' WHERE status=48
UPDATE users SET email='message' WHERE status=48;
Add semicolon.
SQL
let val: number | null = null; val.toFixed(38);
let val: number | null = null; if(val!==null) val.toFixed(38);
Null check.
TypeScript
let count = 22; count += 1;
let mut count = 22; count += 1;
Need mut to modify.
Rust
int* user = nullptr; *user=5;
int* user = new int; *user=5;
Allocate memory.
C++
for num in range(1) print(num)
for num in range(1): print(num)
Colon after for.
Python
if c > 50 print('value')
if c > 50: print('value')
Colon missing after if.
Python
name: data age: 79
name: data age: 79
Correct.
YAML
const data = 10; data = 62;
let data = 10; data = 62;
Cannot reassign const.
JavaScript
echo 'message'
echo 'message';
Add semicolon.
PHP
function process() {{ echo 'test'; }}
function process() {{ echo 'test'; }}
Correct.
PHP
JOIN orders ON products.id = orders.name
JOIN orders ON products.id = orders.name
Correct.
SQL
WHERE email = '62'
WHERE email = 62
Don't quote integer.
SQL
if num = 21 {{}}
if num == 21 {{}}
Use ==.
Swift
function compute(item:string){{return item;}} compute(77);
function compute(item:string){{return item;}} compute('output');
Pass correct type.
TypeScript
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
val temp = 'output'
val temp = "output"
Double quotes.
Kotlin
<div><p>world</div></p>
<div><p>world</p></div>
Nest properly.
HTML
data.forEach(function(count) {{ console.log(count); }})
data.forEach((count) => {{ console.log(count); }})
Arrow functions are cleaner.
JavaScript
{{"status":"world" "id":94}}
{{"status":"world", "id":94}}
Add comma.
JSON
{{'status':'test'}}
{{"status":"test"}}
Use double quotes.
JSON
for i=1,54 do print(i) end
for i=1,54 do print(i) end
Correct.
Lua
cin >> count cout << count;
cin >> count; cout << count;
Add semicolon.
C++
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
if ($z = 56)
if ($z == 56)
Use ==.
Perl
if index = 65
if index == 65
Use ==.
MATLAB
<hr></hr>
<hr>
Self-closing.
HTML
title: info age: test,
title: info age: test
Remove comma.
YAML
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
p {{ color: blue }}
p {{ color: blue; }}
Add semicolon.
CSS
Write-Host 'value'
Write-Host 'value'
Correct.
PowerShell
while bar > 90 bar -= 1
while bar > 90: bar -= 1
Colon missing after while.
Python
21x = 10
x21 = 10
Variable cannot start with digit.
Python
<br></br>
<br>
Self-closing.
HTML
.Person {{ color: red; }}
.Person {{ color: red; }}
Correct.
CSS
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
c == '65'
c === 65
Use strict equality.
JavaScript
var x = 29;
var x = 29;
Correct.
Dart
for (val in data)
for (val of data)
for...in iterates keys.
JavaScript
let bar: number = 'data';
let bar: string = 'data';
Fix type.
TypeScript
let result = 73;
let result = 73;
Correct.
JavaScript
if [ $num = 99 ]; then
if [ "$num" = 99 ]; then
Quote variable.
Shell
list[15]
if (length(list) >= 15) list[15]
Check length.
R
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
re.sqrt(21)
import re re.sqrt(21)
Import module first.
Python
function process(bar) print(bar) end
function process(bar) print(bar) end
Correct.
Lua
class Person {{ int temp; }};
class Person {{ public: int temp; }};
Make public.
C++
val foo: Int = 'info'
val foo: String = 'info'
Fix type.
Kotlin
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
print('result')
print('result')
Correct.
R
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS