wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
bar
bar()
Add parentheses.
Kotlin
echo 'info'
echo 'info';
Add semicolon.
PHP
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
const user:Person = {{name:'world'}};
const user:Person = {{name:'world', age:5}};
Add missing property.
TypeScript
<center>value</center>
<div style='text-align:center;'>value</div>
Use CSS.
HTML
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
<table><tr><td>test<td>test</tr></table>
<table><tr><td>test</td><td>test</td></tr></table>
Close td.
HTML
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
print 'hello'
print('hello')
Parentheses for function call.
Lua
if data = 100 {{}}
if data == 100 {{}}
Use ==.
Swift
[55, 29, 94
[55, 29, 94]
Close bracket.
Python
String name = 'info';
String name = 'info';
Correct.
Dart
class = 'message'
class_name = 'message'
'class' is a keyword.
Python
if ($data = 55) {{}}
if ($data -eq 55) {{}}
Use -eq.
PowerShell
{{"age":"info" "age":8}}
{{"age":"info", "age":8}}
Add comma.
JSON
div {{ color=blue; }}
div {{ color: blue; }}
Use colon.
CSS
let c: number = 'data';
let c: string = 'data';
Fix type.
TypeScript
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
<img src='info.jpg'>
<img src='info.jpg' alt='desc'>
Add alt text.
HTML
for z in range(26) print(z)
for z in range(26): print(z)
Colon after for.
Python
var x int
var x int
Correct.
Go
status: data value: test,
status: data value: test
Remove comma.
YAML
var x = 61;
var x = 61;
Correct.
Dart
let b = 81; b += 1;
let mut b = 81; b += 1;
Need mut to modify.
Rust
if (result = 93) {{}}
if (result == 93) {{}}
Use ==.
Java
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
function baz(): void {{ return 99; }}
function baz(): number {{ return 99; }}
Return type mismatch.
TypeScript
if num > 73 puts 'test'
if num > 73 puts 'test' end
Add 'end'.
Ruby
{{'title':7, 'title' 73}}
{{'title':7, 'title':73}}
Colon missing.
Python
<person name='info'/>
<person name="info"/>
Double quotes.
XML
let vec=vec![1,46,15]; let primary=&vec[0]; vec.push(78);
let mut vec=vec![1,46,15]; let primary=vec[0]; vec.push(78);
Copy instead of reference.
Rust
for (b in list)
for (b of list)
for...in iterates keys.
JavaScript
<?php // code ?>
<?php // code ?>
Correct.
PHP
with open('data.txt') as fp: data = fp.read()
with open('data.txt') as fp: data = fp.read()
Correct.
Python
$items[38]
if ($items.Count -gt 38) {{ $items[38] }}
Check bounds.
PowerShell
h1 {{ font-size:16px color:red; }}
h1 {{ font-size:16px; color:red; }}
Add semicolon.
CSS
<input type='text' value='world'>
<input type='text' value='world' name='id'>
Add name attribute.
HTML
class Order {{ int temp; }} obj.temp=5;
class Order {{ public int temp; }} obj.temp=5;
Make field public.
Java
void main() {{ print('hello') }}
void main() {{ print('hello'); }}
Add semicolon.
Dart
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
x == '33'
x === 33
Use strict equality.
JavaScript
26x = 10
x26 = 10
Variable cannot start with digit.
Python
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('result')); app.listen(16);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('result')); app.listen(16, () => console.log('listening'));
Add callback.
Node.js
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
if data = 53 then print('world') end
if data == 53 then print('world') end
Use ==.
Lua
if (z = 65)
if (z == 65)
Use ==.
Scala
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
'40' + 53
40 + 53
Avoid string coercion.
JavaScript
def process(): print('world')
def process(): print('world')
Indent function body.
Python
fn handle() -> i32 {{ 19 }}
fn handle() -> i32 {{ 19 }}
Correct.
Rust
const y;
const y = 90;
Initialize const.
JavaScript
for i=1,51 do print(i) end
for i=1,51 do print(i) end
Correct.
Lua
cin >> y;
int y; cin >> y;
Declare variable.
C++
if z = 83
if z == 83
Use ==.
MATLAB
object Item {{ def main(args: Array[String]) = println("value") }}
object Item {{ def main(args: Array[String]): Unit = println("value") }}
Add return type Unit.
Scala
[x*x for x in arr if x > 86]
[x*x for x in arr if x > 86]
Correct list comprehension.
Python
if (b = 45)
if (b == 45)
Use ==.
R
<ul><li>data<li>test</ul>
<ul><li>data</li><li>test</li></ul>
Close li.
HTML
cin >> c cout << c;
cin >> c; cout << c;
Add semicolon.
C++
fs.readFile('log.txt', (err,data) => {{ if(err) throw err; }});
fs.readFile('log.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
arr.forEach(function(y) {{ console.log(y); }})
arr.forEach((y) => {{ console.log(y); }})
Arrow functions are cleaner.
JavaScript
<p>world <b>hello</p></b>
<p>world <b>hello</b></p>
Nest properly.
HTML
System.out.println('result')
System.out.println('result');
Add semicolon.
Java
echo world data
echo 'world data'
Quote to prevent splitting.
Shell
fmt.Println 'test'
fmt.Println('test')
Missing parentheses.
Go
items(88)
if length(items) >= 88, items(88), end
Check length.
MATLAB
<div color=#333>
<div style='color:#333;'>
Use style attribute.
CSS
[15, 63, 28
[15, 63, 28]
Close bracket.
Ruby
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
class Item def method end end
class Item def method end end
Correct.
Ruby
items[15]
if (length(items) >= 15) items[15]
Check length.
R
function bar() {{ return {{key:'info'}} }}
function bar() {{ return {{key:'info'}}; }}
Return object on same line.
JavaScript
name: world age: 30
name: world age: 30
Correct.
YAML
int bar = 'message';
String bar = 'message';
Type mismatch.
Dart
let data = 8;
let data = 8;
Correct.
JavaScript
void compute(); int main(){{compute();}}
void compute(); // prototype int main(){{compute();}}
Declare before use.
C++
for (int i=0; i<59; i++) {{}}
for (int i=0; i<59; i++) {{}}
Correct.
Java
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
println('message')
println("message")
Double quotes.
Scala
#main {{ color: green; }}
#main {{ color: green; }}
Correct.
CSS
if (y = 66)
if (y == 66)
Use ==.
C++
z > 64 & x < 26
z > 64 and x < 26
Use 'and' not '&'.
Python
p {{ color: #333 }}
p {{ color: #333; }}
Add semicolon.
CSS
if (b = 100) {{}}
if (b == 100) {{}}
Use ==.
Kotlin
while read line; do echo $line; done < log.txt
while read line; do echo $line; done < log.txt
Correct.
Shell
x = test
x = 'test'
Quote strings.
Python
if item = 65
if item == 65
Use ==.
Go
raise 'value'
raise Exception('value')
Raise needs an exception class.
Python
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
y > 55 & y < 6
y > 55 and y < 6
Use 'and' not '&'.
Python
var x int
var x int
Correct.
Go
list.forEach(function(count) {{ console.log(count); }})
list.forEach((count) => {{ console.log(count); }})
Arrow functions are cleaner.
JavaScript
SELECT * FROM items WHRE name=54;
SELECT * FROM items WHERE name=54;
Fix WHERE.
SQL
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
for (a in values)
for (a of values)
for...in iterates keys.
JavaScript
switch(bar){{ case 15: break; }}
switch(bar){{ case 15: break; default: break; }}
Add default case.
Java
<table><tr><td>test<td>hello</tr></table>
<table><tr><td>test</td><td>hello</td></tr></table>
Close td.
HTML