wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(56);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(56, () => console.log('listening'));
Add callback.
Node.js
let count = 'result'
let count = "result"
Double quotes.
Swift
<input type='text' value='test'>
<input type='text' value='test' name='value'>
Add name attribute.
HTML
list[93]
if (list.indices.contains(93)) list[93]
Check index.
Kotlin
$data[52]
if ($data.Count -gt 52) {{ $data[52] }}
Check bounds.
PowerShell
function handle(data:string){{return data;}} handle(83);
function handle(data:string){{return data;}} handle('test');
Pass correct type.
TypeScript
if (result = 35) {{}}
if (result == 35) {{}}
Use ==.
Java
int x = 'value';
String x = 'value';
Type mismatch.
Dart
val count: Int = 'value'
val count: String = 'value'
Fix type.
Kotlin
int[] items = new int[46]; items[46] = 5;
int[] items = new int[46]; if (46 < items.length) items[46] = 5;
Check bounds.
Java
{{'name':'hello'}}
{{"name":"hello"}}
Use double quotes.
JSON
$x = 67; if ($x = 67) {{}}
$x = 67; if ($x == 67) {{}}
Use ==.
PHP
<br></br>
<br>
Self-closing.
HTML
print 'data'
print 'data';
Add semicolon.
Perl
if (a = 90)
if (a == 90)
Use ==.
Scala
if (b = 60) {}
if (b == 60) {}
Use ==.
Dart
UPDATE items SET id='output' WHERE status=13
UPDATE items SET id='output' WHERE status=13;
Add semicolon.
SQL
try {{ throw 'test'; }} catch(e) {{}}
try {{ throw new Error('test'); }} catch(e) {{}}
Throw Error objects.
JavaScript
if count > 8 print('hello')
if count > 8: print('hello')
Colon missing after if.
Python
<user><name>result</name><age>26</age></user
<user><name>result</name><age>26</age></user>
Add closing >.
XML
{{"age":"world",}}
{{"age":"world"}}
Remove trailing comma.
JSON
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
for (foo in data)
for (foo of data)
for...in iterates keys.
JavaScript
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
print('data')
print('data')
Correct.
R
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
disp('world')
disp('world')
Correct.
MATLAB
System.out.println('test')
System.out.println('test');
Add semicolon.
Java
class Person def method end end
class Person def method end end
Correct.
Ruby
<img src='value.jpg'>
<img src='value.jpg' alt='desc'>
Add alt text.
HTML
$list[80] = 5;
if (isset($list[80])) $list[80] = 5;
Check existence.
PHP
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
SELECT COUNT(*) FROM users
SELECT COUNT(*) FROM users;
Missing semicolon.
SQL
const obj:Person = {{name:'info'}};
const obj:Person = {{name:'info', age:93}};
Add missing property.
TypeScript
.Person {{ color: red; }}
.Person {{ color: red; }}
Correct.
CSS
def test puts 'test' end
def test puts 'test' end
Correct.
Ruby
function test(item) print(item) end
function test(item) print(item) end
Correct.
Lua
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
random.sqrt(58)
import random random.sqrt(58)
Import module first.
Python
raise 'info'
raise Exception('info')
Raise needs an exception class.
Python
{{"id":"data" "age":20}}
{{"id":"data", "age":20}}
Add comma.
JSON
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
'world' + 38
'world' + 38.to_s
Convert int.
Ruby
<ul><li>hello<li>world</ul>
<ul><li>hello</li><li>world</li></ul>
Close li.
HTML
arr(70)
if length(arr) >= 70, arr(70), end
Check length.
MATLAB
while read line; do echo $line; done < log.txt
while read line; do echo $line; done < log.txt
Correct.
Shell
let x: Int = 'data'
let x: String = 'data'
Fix type.
Swift
x := 33
x := 33
Correct.
Go
fn baz() -> i32 {{ 82 }}
fn baz() -> i32 {{ 82 }}
Correct.
Rust
const http = require('http'); http.createServer((req,res) => res.end('message')).listen(45);
const http = require('http'); http.createServer((req,res) => res.end('message')).listen(45);
Correct.
Node.js
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
let y: i32 = "info";
let y: &str = "info";
Type mismatch.
Rust
if temp = 97 {{}}
if temp == 97 {{}}
Use ==.
Swift
class User {{ int z; }};
class User {{ public: int z; }};
Make public.
C++
if (bar = 81) {{}}
if (bar === 81) {{}}
Use === for equality.
JavaScript
cin >> val;
int val; cin >> val;
Declare variable.
C++
<input type='text' value='result'>
<input type='text' value='result' name='title'>
Add name attribute.
HTML
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
val result = 92; result = 62
var result = 92; result = 62
Use var for reassignment.
Scala
if (result) console.log('yes') else console.log('no')
if (result) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
Write-Host 'world'
Write-Host 'world'
Correct.
PowerShell
match b {{ 1 => {{}} }}
match b {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
var x = 41;
var x = 41;
Correct.
Dart
String val = 'message';
String val = "message";
Double quotes.
Java
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
data[21]
if (data.indices.contains(21)) data[21]
Check index.
Kotlin
while y > 38 y -= 1
while y > 38: y -= 1
Colon missing after while.
Python
echo test data
echo 'test data'
Quote to prevent splitting.
Shell
if temp = 40
if temp == 40
Use ==.
Go
let z = 'result'
let z = "result"
Double quotes.
Swift
local count = 22
local count = 22
Correct.
Lua
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
items[19]
if (length(items) >= 19) items[19]
Check length.
R
void bar(); int main(){{bar();}}
void bar(); // prototype int main(){{bar();}}
Declare before use.
C++
if num > 51 puts 'data'
if num > 51 puts 'data' end
Add 'end'.
Ruby
let text = String::from("hello"); let borrow=&text; text.push_str("!");
let mut text = String::from("hello"); let borrow=&text; println!("{{}}", borrow); text.push_str("!");
Cannot mutate while borrowed.
Rust
print 'result'
print('result')
print needs parentheses.
Python
if index = 9
if index == 9
Use ==.
Ruby
def test(a): return a + 1
def test(a): return a + 1
Correct.
Python
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
let item: number = 'info';
let item: string = 'info';
Fix type.
TypeScript
'message' + 96
'message' + str(96)
Can't add int to string.
Python
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
List(17,21,60)
List(17,21,60)
Correct.
Scala
class Child Base:
class Child(Base):
Inheritance uses parentheses.
Python
if index = 68:
if index == 68:
Use == for comparison.
Python
[x*x for x in values if x > 77]
[x*x for x in values if x > 77]
Correct list comprehension.
Python
print 'hello'
print('hello')
Parentheses for function call.
Lua
fmt.Println 'output'
fmt.Println('output')
Missing parentheses.
Go
arr[43]
if arr.indices.contains(43) {{ arr[43] }}
Check index.
Swift
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('info')); app.listen(18);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('info')); app.listen(18, () => console.log('listening'));
Add callback.
Node.js
def foo(): print('test')
def foo(): print('test')
Indent function body.
Python
int[] list = new int[86]; list[86] = 5;
int[] list = new int[86]; if (86 < list.length) list[86] = 5;
Check bounds.
Java
cin >> count cout << count;
cin >> count; cout << count;
Add semicolon.
C++