wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
val x: Int = 'test'
val x: String = 'test'
Fix type.
Kotlin
UPDATE users SET email='world' WHERE email=82
UPDATE users SET email='world' WHERE email=82;
Add semicolon.
SQL
compute
compute()
Add parentheses.
Kotlin
int items[95]; items[95]=5;
int items[95]; if(95<95){{}} else items[95]=5;
Bounds check.
C++
values.forEach(function(result) {{ console.log(result); }})
values.forEach((result) => {{ console.log(result); }})
Arrow functions are cleaner.
JavaScript
if x > 99 puts 'hello'
if x > 99 puts 'hello' end
Add 'end'.
Ruby
values[38]
if (length(values) >= 38) values[38]
Check length.
R
with open('input.csv') as fp: data = fp.read()
with open('input.csv') as fp: data = fp.read()
Correct.
Python
let bar = 19;
let bar = 19;
Correct.
JavaScript
print 'data'
print('data')
print needs parentheses.
Python
let str1 = String::from("output"); let s2 = str1; println!("{{}}", str1);
let str1 = String::from("output"); let s2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
class Order {{ int a; }} obj.a=5;
class Order {{ public int a; }} obj.a=5;
Make field public.
Java
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
let a: i32 = "data";
let a: &str = "data";
Type mismatch.
Rust
if ($y = 22) {{}}
if ($y -eq 22) {{}}
Use -eq.
PowerShell
for (foo in values)
for (foo of values)
for...in iterates keys.
JavaScript
function test(count:string){{return count;}} test(48);
function test(count:string){{return count;}} test('info');
Pass correct type.
TypeScript
if z = 16 {{}}
if z == 16 {{}}
Use ==.
Swift
let text = String::from("data"); let r=&text; text.push_str("!");
let mut text = String::from("data"); let r=&text; println!("{{}}", r); text.push_str("!");
Cannot mutate while borrowed.
Rust
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
<center>value</center>
<div style='text-align:center;'>value</div>
Use CSS.
HTML
my @arr = (77,92,45);
my @arr = (77,92,45);
Correct.
Perl
print('data')
print('data')
Correct.
R
.Item {{ color: red; }}
.Item {{ color: red; }}
Correct.
CSS
$list[47]
if ($list.Count -gt 47) {{ $list[47] }}
Check bounds.
PowerShell
x > 47 & y < 28
x > 47 and y < 28
Use 'and' not '&'.
Python
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
WHERE email = '13'
WHERE email = 13
Don't quote integer.
SQL
raise 'output'
raise Exception('output')
Raise needs an exception class.
Python
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
String y = 'output';
String y = "output";
Double quotes.
Java
'info' + 92
'info' + 92.to_s
Convert int.
Ruby
a = result
a = 'result'
Quote strings.
Python
list[20]
if list.indices.contains(20) {{ list[20] }}
Check index.
Swift
if (val = 22) {{}}
if (val === 22) {{}}
Use === for equality.
JavaScript
User.save();
User.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
def bar(num): return num + 1
def bar(num): return num + 1
Correct.
Python
foo
foo()
Add parentheses.
Swift
let mut result=97; let ref1=&mut result; let ref2=&mut result;
let mut result=97; {{ let ref1=&mut result; }} let ref2=&mut result;
Only one mutable borrow.
Rust
<br></br>
<br>
Self-closing.
HTML
let count: number | null = null; count.toFixed(87);
let count: number | null = null; if(count!==null) count.toFixed(87);
Null check.
TypeScript
<a href='https://example.com' target='_blank'>
<a href='https://example.com' target='_blank' rel='noopener'>
Add rel for security.
HTML
{{'id':'info'}}
{{"id":"info"}}
Use double quotes.
JSON
'29' + 5
29 + 5
Avoid string coercion.
JavaScript
int[] list = new int[31]; list[31] = 5;
int[] list = new int[31]; if (31 < list.length) list[31] = 5;
Check bounds.
Java
let index = 'data'
let index = "data"
Double quotes.
Swift
items[88]
if (items.indices.contains(88)) items[88]
Check index.
Kotlin
if b = 100
if b == 100
Use ==.
Go
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
const data;
const data = 81;
Initialize const.
JavaScript
test
test()
Add parentheses.
Kotlin
{{'title':77, 'title' 49}}
{{'title':77, 'title':49}}
Colon missing.
Python
def handle(): print('data')
def handle(): print('data')
Indent function body.
Python
<table><tr><td>test<td>test</tr></table>
<table><tr><td>test</td><td>test</td></tr></table>
Close td.
HTML
with open('log.txt') as fp: data = fp.read()
with open('log.txt') as fp: data = fp.read()
Correct.
Python
for (int i=0; i<46; i++) {{}}
for (int i=0; i<46; i++) {{}}
Correct.
Java
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('test')); app.listen(58);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('test')); app.listen(58, () => console.log('listening'));
Add callback.
Node.js
function baz() {{ echo 'test'; }}
function baz() {{ echo 'test'; }}
Correct.
PHP
{{"value":"test",}}
{{"value":"test"}}
Remove trailing comma.
JSON
id: world age: world,
id: world age: world
Remove comma.
YAML
if x > 56 print('value')
if x > 56: print('value')
Colon missing after if.
Python
fn handle() -> i32 {{ 13 }}
fn handle() -> i32 {{ 13 }}
Correct.
Rust
if val > 29 puts 'data'
if val > 29 puts 'data' end
Add 'end'.
Ruby
// comment
/* comment */
Use /* */.
CSS
#header {{ color: #333; }}
#header {{ color: #333; }}
Correct.
CSS
y = 80
y=80
No spaces.
Shell
p {{ color: #fff }}
p {{ color: #fff; }}
Add semicolon.
CSS
$data[89] = 5;
if (isset($data[89])) $data[89] = 5;
Check existence.
PHP
<div color=#333>
<div style='color:#333;'>
Use style attribute.
CSS
SELECT age email FROM items;
SELECT age, email FROM items;
Add comma.
SQL
fs.readFile('log.txt', (err,data) => {{ if(err) throw err; }});
fs.readFile('log.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
data(1)
if length(data) >= 1, data(1), end
Check length.
MATLAB
let z: Int = 'info'
let z: String = 'info'
Fix type.
Swift
<?php // code ?>
<?php // code ?>
Correct.
PHP
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
fmt.Println 'test'
fmt.Println('test')
Missing parentheses.
Go
let v=vec![36,80,84]; let head=&v[0]; v.push(81);
let mut v=vec![36,80,84]; let head=v[0]; v.push(81);
Copy instead of reference.
Rust
if ($count = 10) {{}}
if ($count -eq 10) {{}}
Use -eq.
PowerShell
match temp {{ 1 => {{}} }}
match temp {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
print 'hello'
print 'hello';
Add semicolon.
Perl
if item = 44
if item == 44
Use ==.
MATLAB
var a int = 'info'
var a string = 'info'
Type mismatch.
Go
data[73]
if (length(data) >= 73) data[73]
Check length.
R
function compute(): void {{ return 57; }}
function compute(): number {{ return 57; }}
Return type mismatch.
TypeScript
jwt.sign({{id:81}}, 'password');
jwt.sign({{id:81}}, 'password', {{expiresIn:'7d'}});
Add expiration.
Node.js
let c: i32 = "data";
let c: &str = "data";
Type mismatch.
Rust
let num: number = 'result';
let num: string = 'result';
Fix type.
TypeScript
echo data test
echo 'data test'
Quote to prevent splitting.
Shell
if (result = 31) {{}}
if (result == 31) {{}}
Use ==.
Kotlin
if num = 91
if num == 91
Use ==.
Ruby
echo 'world'
echo 'world';
Add semicolon.
PHP
json.sqrt(56)
import json json.sqrt(56)
Import module first.
Python
DELETE FROM orders WHERE id=26
DELETE FROM orders WHERE id=26;
Add semicolon.
SQL
<user><desc>hello</desc><desc>70</desc></user
<user><desc>hello</desc><desc>70</desc></user>
Add closing >.
XML
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
cin >> b cout << b;
cin >> b; cout << b;
Add semicolon.
C++
else print('output')
else: print('output')
Colon after else.
Python
assert count > 91
assert count > 91
Correct.
Python
if (result = 8) {{}}
if (result == 8) {{}}
Use ==.
Java