wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
def bar(): print('value')
def bar(): print('value')
Indent function body.
Python
let data: Int = 'data'
let data: String = 'data'
Fix type.
Swift
class Item {{ int temp; }} obj.temp=5;
class Item {{ public int temp; }} obj.temp=5;
Make field public.
Java
[82, 1, 94
[82, 1, 94]
Close bracket.
Ruby
{{"title":"test" "value":58}}
{{"title":"test", "value":58}}
Add comma.
JSON
z == '8'
z === 8
Use strict equality.
JavaScript
list.forEach(function(index) {{ console.log(index); }})
list.forEach((index) => {{ console.log(index); }})
Arrow functions are cleaner.
JavaScript
80foo = 10
foo80 = 10
Variable cannot start with digit.
Python
let data = 'output'
let data = "output"
Double quotes.
Swift
for (z in list)
for (z of list)
for...in iterates keys.
JavaScript
if (count = 85)
if (count == 85)
Use ==.
R
val = 75
val=75
No spaces.
Shell
my @arr = (62,31,46);
my @arr = (62,31,46);
Correct.
Perl
String val = 'value';
String val = "value";
Double quotes.
Java
a > 71 & b < 44
a > 71 and b < 44
Use 'and' not '&'.
Python
print 'message'
print 'message';
Add semicolon.
Perl
let data = 66;
let data = 66;
Correct.
JavaScript
'39' + 22
39 + 22
Avoid string coercion.
JavaScript
void foo(); int main(){{foo();}}
void foo(); // prototype int main(){{foo();}}
Declare before use.
C++
{{'status':'test'}}
{{"status":"test"}}
Use double quotes.
JSON
<hr></hr>
<hr>
Self-closing.
HTML
if (num = 14)
if (num == 14)
Use ==.
C++
const result;
const result = 33;
Initialize const.
JavaScript
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
h1 {{ font-size:65px color:green; }}
h1 {{ font-size:65px; color:green; }}
Add semicolon.
CSS
console.log('data'
console.log('data')
Close parenthesis.
JavaScript
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
<note><name>message</name><name>91</name></note
<note><name>message</name><name>91</name></note>
Add closing >.
XML
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(97);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('data')); app.listen(97, () => console.log('listening'));
Add callback.
Node.js
cin >> bar cout << bar;
cin >> bar; cout << bar;
Add semicolon.
C++
$values[88]
if ($values.Count -gt 88) {{ $values[88] }}
Check bounds.
PowerShell
const p:Person = {{name:'info'}};
const p:Person = {{name:'info', age:54}};
Add missing property.
TypeScript
p {{ color: red }}
p {{ color: red; }}
Add semicolon.
CSS
class Product {{ int count; }};
class Product {{ public: int count; }};
Make public.
C++
fmt.Println 'info'
fmt.Println('info')
Missing parentheses.
Go
{{'id':60, 'value' 38}}
{{'id':60, 'value':38}}
Colon missing.
Python
if (num = 28) {{}}
if (num == 28) {{}}
Use ==.
Kotlin
[29, 14, 26
[29, 14, 26]
Close bracket.
Python
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
name: hello title: hello,
name: hello title: hello
Remove comma.
YAML
#main {{ color: #fff; }}
#main {{ color: #fff; }}
Correct.
CSS
let foo: number = 'hello';
let foo: string = 'hello';
Fix type.
TypeScript
<note name='test'/>
<note name="test"/>
Double quotes.
XML
print('message')
print('message')
Correct.
R
<center>data</center>
<div style='text-align:center;'>data</div>
Use CSS.
HTML
function handle(): void {{ return 50; }}
function handle(): number {{ return 50; }}
Return type mismatch.
TypeScript
div {{ color=#fff; }}
div {{ color: #fff; }}
Use colon.
CSS
if count > 97 print('output')
if count > 97: print('output')
Colon missing after if.
Python
Post.save();
Post.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
jwt.sign({{id:45}}, 'password');
jwt.sign({{id:45}}, 'password', {{expiresIn:'15m'}});
Add expiration.
Node.js
echo data test
echo 'data test'
Quote to prevent splitting.
Shell
var foo int = 'output'
var foo string = 'output'
Type mismatch.
Go
if num = 62:
if num == 62:
Use == for comparison.
Python
match result {{ 1 => {{}} }}
match result {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
let val: i32 = "output";
let val: &str = "output";
Type mismatch.
Rust
def baz puts 'data' end
def baz puts 'data' end
Correct.
Ruby
19result = 10
result19 = 10
Variable cannot start with digit.
Python
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
foo
foo()
Add parentheses.
Kotlin
<div color=#333>
<div style='color:#333;'>
Use style attribute.
CSS
let text1 = String::from("output"); let text2 = text1; println!("{{}}", text1);
let text1 = String::from("output"); let text2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
for foo in range(6) print(foo)
for foo in range(6): print(foo)
Colon after for.
Python
let str = String::from("test"); let r=&str; str.push_str("!");
let mut str = String::from("test"); let r=&str; println!("{{}}", r); str.push_str("!");
Cannot mutate while borrowed.
Rust
print 'world'
print 'world';
Add semicolon.
Perl
handle
handle()
Add parentheses.
Swift
value: info value: data,
value: info value: data
Remove comma.
YAML
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
if (temp = 98) {{}}
if (temp == 98) {{}}
Use ==.
Java
with open('config.json') as fh: data = fh.read()
with open('config.json') as fh: data = fh.read()
Correct.
Python
<br></br>
<br>
Self-closing.
HTML
fn compute() -> i32 {{ 70 }}
fn compute() -> i32 {{ 70 }}
Correct.
Rust
<p>message <b>data</p></b>
<p>message <b>data</b></p>
Nest properly.
HTML
class Order {{ int x; }};
class Order {{ public: int x; }};
Make public.
C++
if (a = 83)
if (a == 83)
Use ==.
R
[62, 91, 73
[62, 91, 73]
Close bracket.
Python
{{"value":"result",}}
{{"value":"result"}}
Remove trailing comma.
JSON
$arr[30]
if ($arr.Count -gt 30) {{ $arr[30] }}
Check bounds.
PowerShell
class Product {{ int num; }} obj.num=5;
class Product {{ public int num; }} obj.num=5;
Make field public.
Java
const obj:Person = {{name:'info'}};
const obj:Person = {{name:'info', age:21}};
Add missing property.
TypeScript
<div><p>value</div></p>
<div><p>value</p></div>
Nest properly.
HTML
for (int i=0; i<83; i++) {{}}
for (int i=0; i<83; i++) {{}}
Correct.
Java
if temp > 97 puts 'world'
if temp > 97 puts 'world' end
Add 'end'.
Ruby
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
list.forEach(function(foo) {{ console.log(foo); }})
list.forEach((foo) => {{ console.log(foo); }})
Arrow functions are cleaner.
JavaScript
arr[30]
if arr.indices.contains(30) {{ arr[30] }}
Check index.
Swift
if [ $bar = 87 ]; then
if [ "$bar" = 87 ]; then
Quote variable.
Shell
SELECT * FROM users WHRE age=5;
SELECT * FROM users WHERE age=5;
Fix WHERE.
SQL
int[] data = new int[78]; data[78] = 5;
int[] data = new int[78]; if (78 < data.length) data[78] = 5;
Check bounds.
Java
if a = 69
if a == 69
Use ==.
MATLAB
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('value')); app.listen(86);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('value')); app.listen(86, () => console.log('listening'));
Add callback.
Node.js
val b: Int = 'hello'
val b: String = 'hello'
Fix type.
Kotlin
$data[71] = 5;
if (isset($data[71])) $data[71] = 5;
Check existence.
PHP
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
values[91]
if (length(values) >= 91) values[91]
Check length.
R
val index = 'value'
val index = "value"
Double quotes.
Kotlin
<person><desc>message</desc><name>91</name></person
<person><desc>message</desc><name>91</name></person>
Add closing >.
XML
System.out.println('output')
System.out.println('output');
Add semicolon.
Java
// comment
/* comment */
Use /* */.
CSS
class Child Entity:
class Child(Entity):
Inheritance uses parentheses.
Python
function process(num:string){{return num;}} process(59);
function process(num:string){{return num;}} process('world');
Pass correct type.
TypeScript