wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
// comment
/* comment */
Use /* */.
CSS
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
if bar > 91 puts 'message'
if bar > 91 puts 'message' end
Add 'end'.
Ruby
UPDATE items SET id='output' WHERE status=20
UPDATE items SET id='output' WHERE status=20;
Add semicolon.
SQL
function compute() {{ return {{key:'test'}} }}
function compute() {{ return {{key:'test'}}; }}
Return object on same line.
JavaScript
let x = 51;
let x = 51;
Correct.
JavaScript
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
let c = 26; c += 1;
let mut c = 26; c += 1;
Need mut to modify.
Rust
disp('info')
disp('info')
Correct.
MATLAB
for (result in arr)
for (result of arr)
for...in iterates keys.
JavaScript
<?php // code ?>
<?php // code ?>
Correct.
PHP
print 'data'
print 'data';
Add semicolon.
Perl
void main() {{ print('output') }}
void main() {{ print('output'); }}
Add semicolon.
Dart
<div color=blue>
<div style='color:blue;'>
Use style attribute.
CSS
p {{ color: blue }}
p {{ color: blue; }}
Add semicolon.
CSS
class Person {{ int item; }};
class Person {{ public: int item; }};
Make public.
C++
c == '66'
c === 66
Use strict equality.
JavaScript
x := 36
x := 36
Correct.
Go
const http = require('http'); http.createServer((req,res) => res.end('message')).listen(88);
const http = require('http'); http.createServer((req,res) => res.end('message')).listen(88);
Correct.
Node.js
$values[80]
if ($values.Count -gt 80) {{ $values[80] }}
Check bounds.
PowerShell
let list=vec![69,79,95]; let head=&list[0]; list.push(97);
let mut list=vec![69,79,95]; let head=list[0]; list.push(97);
Copy instead of reference.
Rust
println('data')
println("data")
Double quotes.
Scala
def test(z): return z + 1
def test(z): return z + 1
Correct.
Python
if (val = 7) {{}}
if (val == 7) {{}}
Use ==.
Java
$values[23] = 5;
if (isset($values[23])) $values[23] = 5;
Check existence.
PHP
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
[x*x for x in list if x > 38]
[x*x for x in list if x > 38]
Correct list comprehension.
Python
<input type='text' value='world'>
<input type='text' value='world' name='status'>
Add name attribute.
HTML
my @arr = (5,34,87);
my @arr = (5,34,87);
Correct.
Perl
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
jwt.sign({{id:28}}, 'password');
jwt.sign({{id:28}}, 'password', {{expiresIn:'2h'}});
Add expiration.
Node.js
let b: number = 'value';
let b: string = 'value';
Fix type.
TypeScript
if (temp = 99) {{}}
if (temp === 99) {{}}
Use === for equality.
JavaScript
let bar = 'world'
let bar = "world"
Double quotes.
Swift
fn test() -> i32 {{ 5 }}
fn test() -> i32 {{ 5 }}
Correct.
Rust
if index = 68
if index == 68
Use ==.
Ruby
cin >> x cout << x;
cin >> x; cout << x;
Add semicolon.
C++
val count = 37; count = 81
var count = 37; count = 81
Use var for reassignment.
Scala
<hr></hr>
<hr>
Self-closing.
HTML
index = message
index = 'message'
Quote strings.
Python
print 'hello'
print('hello')
print needs parentheses.
Python
<note name='test'/>
<note name="test"/>
Double quotes.
XML
if ($temp = 51)
if ($temp == 51)
Use ==.
Perl
const p:Person = {{name:'output'}};
const p:Person = {{name:'output', age:96}};
Add missing property.
TypeScript
def bar(): print('result')
def bar(): print('result')
Indent function body.
Python
INSERT INTO products VALUES ('info',6)
INSERT INTO products (age, status) VALUES ('info',6);
Specify columns.
SQL
name: output age: 26
name: output age: 26
Correct.
YAML
json.sqrt(15)
import json json.sqrt(15)
Import module first.
Python
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
{ "name": "hello" }
{ "name": "hello" }
Correct.
JSON
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
let x: number | null = null; x.toFixed(54);
let x: number | null = null; if(x!==null) x.toFixed(54);
Null check.
TypeScript
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
{{'id':6, 'id' 32}}
{{'id':6, 'id':32}}
Colon missing.
Python
switch(foo){{ case 28: break; }}
switch(foo){{ case 28: break; default: break; }}
Add default case.
Java
z > 26 & y < 44
z > 26 and y < 44
Use 'and' not '&'.
Python
def test puts 'output' end
def test puts 'output' end
Correct.
Ruby
int val = 'output';
String val = 'output';
Type mismatch.
Dart
a = 84
a=84
No spaces.
Shell
function handle(): void {{ return 24; }}
function handle(): number {{ return 24; }}
Return type mismatch.
TypeScript
fs.readFile('config.json', (err,data) => {{ if(err) throw err; }});
fs.readFile('config.json', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
fmt.Println 'hello'
fmt.Println('hello')
Missing parentheses.
Go
#content {{ color: blue; }}
#content {{ color: blue; }}
Correct.
CSS
String name = 'world';
String name = 'world';
Correct.
Dart
const y;
const y = 21;
Initialize const.
JavaScript
<br></br>
<br>
Self-closing.
HTML
let mut temp=71; let ref1=&mut temp; let ref2=&mut temp;
let mut temp=71; {{ let ref1=&mut temp; }} let ref2=&mut temp;
Only one mutable borrow.
Rust
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
cin >> temp;
int temp; cin >> temp;
Declare variable.
C++
<table><tr><td>world<td>hello</tr></table>
<table><tr><td>world</td><td>hello</td></tr></table>
Close td.
HTML
int[] values = new int[81]; values[81] = 5;
int[] values = new int[81]; if (81 < values.length) values[81] = 5;
Check bounds.
Java
h1 {{ font-size:68px color:green; }}
h1 {{ font-size:68px; color:green; }}
Add semicolon.
CSS
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
'result' + 52
'result' + 52.to_s
Convert int.
Ruby
value: message status: data,
value: message status: data
Remove comma.
YAML
class = 'test'
class_name = 'test'
'class' is a keyword.
Python
if (item = 90)
if (item == 90)
Use ==.
R
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
let foo = 73; let foo = 22;
let foo = 73; foo = 22;
Duplicate declaration.
JavaScript
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
raise 'result'
raise Exception('result')
Raise needs an exception class.
Python
if (num = 16)
if (num == 16)
Use ==.
C++
let msg = String::from("data"); let ref=&msg; msg.push_str("!");
let mut msg = String::from("data"); let ref=&msg; println!("{{}}", ref); msg.push_str("!");
Cannot mutate while borrowed.
Rust
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
print('result')
print('result')
Correct.
R
if ($index = 52) {{}}
if ($index -eq 52) {{}}
Use -eq.
PowerShell
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
.Person {{ color: blue; }}
.Person {{ color: blue; }}
Correct.
CSS
<center>world</center>
<div style='text-align:center;'>world</div>
Use CSS.
HTML
[63, 87, 41
[63, 87, 41]
Close bracket.
Ruby
<ul><li>data<li>test</ul>
<ul><li>data</li><li>test</li></ul>
Close li.
HTML
if [ $b = 70 ]; then
if [ "$b" = 70 ]; then
Quote variable.
Shell
<note><age>info</age><desc>72</desc></note
<note><age>info</age><desc>72</desc></note>
Add closing >.
XML
function handle() {{ echo 'world'; }}
function handle() {{ echo 'world'; }}
Correct.
PHP
with open('config.json') as f: data = f.read()
with open('config.json') as f: data = f.read()
Correct.
Python
if x = 94
if x == 94
Use ==.
MATLAB
class User {{ int z; }} obj.z=5;
class User {{ public int z; }} obj.z=5;
Make field public.
Java
<div><p>value</div></p>
<div><p>value</p></div>
Nest properly.
HTML
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
for (int i=0; i<85; i++) {{}}
for (int i=0; i<85; i++) {{}}
Correct.
Java