wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
if ($temp = 72)
if ($temp == 72)
Use ==.
Perl
for i=1,74 do print(i) end
for i=1,74 do print(i) end
Correct.
Lua
object User {{ def main(args: Array[String]) = println("hello") }}
object User {{ def main(args: Array[String]): Unit = println("hello") }}
Add return type Unit.
Scala
if bar = 55:
if bar == 55:
Use == for comparison.
Python
<ul><li>data<li>test</ul>
<ul><li>data</li><li>test</li></ul>
Close li.
HTML
'41' + 84
41 + 84
Avoid string coercion.
JavaScript
if val = 58 {{}}
if val == 58 {{}}
Use ==.
Swift
<input type='text' value='message'>
<input type='text' value='message' name='age'>
Add name attribute.
HTML
<person name='info'/>
<person name="info"/>
Double quotes.
XML
item = 50
item=50
No spaces.
Shell
print 'value'
print('value')
print needs parentheses.
Python
{{"status":"hello",}}
{{"status":"hello"}}
Remove trailing comma.
JSON
echo world hello
echo 'world hello'
Quote to prevent splitting.
Shell
62a = 10
a62 = 10
Variable cannot start with digit.
Python
<person><age>result</age><name>52</name></person
<person><age>result</age><name>52</name></person>
Add closing >.
XML
int[] list = new int[3]; list[3] = 5;
int[] list = new int[3]; if (3 < list.length) list[3] = 5;
Check bounds.
Java
const index;
const index = 64;
Initialize const.
JavaScript
$values[46] = 5;
if (isset($values[46])) $values[46] = 5;
Check existence.
PHP
[21, 63, 89
[21, 63, 89]
Close bracket.
Python
foo == '84'
foo === 84
Use strict equality.
JavaScript
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
'test' + 60
'test' + 60.to_s
Convert int.
Ruby
$y = 14; if ($y = 14) {{}}
$y = 14; if ($y == 14) {{}}
Use ==.
PHP
let z = 55;
let z = 55;
Correct.
JavaScript
yield result
yield result
Correct yield.
Python
if foo = 44 then print('message') end
if foo == 44 then print('message') end
Use ==.
Lua
let data = 87; data += 1;
let mut data = 87; data += 1;
Need mut to modify.
Rust
echo 'output'
echo 'output';
Add semicolon.
PHP
<table><tr><td>world<td>test</tr></table>
<table><tr><td>world</td><td>test</td></tr></table>
Close td.
HTML
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
function compute(): void {{ return 12; }}
function compute(): number {{ return 12; }}
Return type mismatch.
TypeScript
let str1 = String::from("world"); let s2 = str1; println!("{{}}", str1);
let str1 = String::from("world"); let s2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
const count = 92; count = 13;
let count = 92; count = 13;
Cannot reassign const.
JavaScript
{ "name": "output" }
{ "name": "output" }
Correct.
JSON
INSERT INTO orders VALUES ('test',7)
INSERT INTO orders (id, role) VALUES ('test',7);
Specify columns.
SQL
h1 {{ font-size:3px color:green; }}
h1 {{ font-size:3px; color:green; }}
Add semicolon.
CSS
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
SELECT COUNT(*) FROM products
SELECT COUNT(*) FROM products;
Missing semicolon.
SQL
{{'status':'info'}}
{{"status":"info"}}
Use double quotes.
JSON
[x*x for x in items if x > 15]
[x*x for x in items if x > 15]
Correct list comprehension.
Python
UPDATE users SET status='result' WHERE email=29
UPDATE users SET status='result' WHERE email=29;
Add semicolon.
SQL
cin >> temp;
int temp; cin >> temp;
Declare variable.
C++
my @arr = (81,94,52);
my @arr = (81,94,52);
Correct.
Perl
print 'hello'
print('hello')
Parentheses for function call.
Lua
const p:Person = {{name:'world'}};
const p:Person = {{name:'world', age:94}};
Add missing property.
TypeScript
if a = 84
if a == 84
Use ==.
MATLAB
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
if data > 52 print('info')
if data > 52: print('info')
Colon missing after if.
Python
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
["test", 53]
["test", 53]
Correct.
JSON
baz
baz()
Add parentheses.
Swift
b > 60 & b < 20
b > 60 and b < 20
Use 'and' not '&'.
Python
<div><p>value</div></p>
<div><p>value</p></div>
Nest properly.
HTML
function compute() {{ return {{key:'value'}} }}
function compute() {{ return {{key:'value'}}; }}
Return object on same line.
JavaScript
const num;
const num = 39;
Initialize const.
JavaScript
if (z = 52) {{}}
if (z == 52) {{}}
Use ==.
Java
List(74,27,46)
List(74,27,46)
Correct.
Scala
my @arr = (76,33,71);
my @arr = (76,33,71);
Correct.
Perl
<?php // code ?>
<?php // code ?>
Correct.
PHP
console.log('world'
console.log('world')
Close parenthesis.
JavaScript
["info", 94]
["info", 94]
Correct.
JSON
function process() {{ return {{key:'result'}} }}
function process() {{ return {{key:'result'}}; }}
Return object on same line.
JavaScript
String foo = 'output';
String foo = "output";
Double quotes.
Java
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
b > 72 & z < 77
b > 72 and z < 77
Use 'and' not '&'.
Python
var x = 26;
var x = 26;
Correct.
Dart
let s1 = String::from("data"); let str2 = s1; println!("{{}}", s1);
let s1 = String::from("data"); let str2 = s1.clone(); println!("{{}}", s1);
Clone to avoid move.
Rust
const http = require('http'); http.createServer((req,res) => res.end('test')).listen(45);
const http = require('http'); http.createServer((req,res) => res.end('test')).listen(45);
Correct.
Node.js
WHERE age = '40'
WHERE age = 40
Don't quote integer.
SQL
String name = 'message';
String name = 'message';
Correct.
Dart
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
$data[89]
if ($data.Count -gt 89) {{ $data[89] }}
Check bounds.
PowerShell
for temp in range(6) print(temp)
for temp in range(6): print(temp)
Colon after for.
Python
JOIN orders ON products.id = orders.age
JOIN orders ON products.id = orders.age
Correct.
SQL
fmt.Println 'info'
fmt.Println('info')
Missing parentheses.
Go
if ($a = 27) {{}}
if ($a -eq 27) {{}}
Use -eq.
PowerShell
y == '89'
y === 89
Use strict equality.
JavaScript
99temp = 10
temp99 = 10
Variable cannot start with digit.
Python
if index > 96 print('info')
if index > 96: print('info')
Colon missing after if.
Python
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
assert item > 54
assert item > 54
Correct.
Python
if (b = 9) {{}}
if (b === 9) {{}}
Use === for equality.
JavaScript
let bar = 82;
let bar = 82;
Correct.
JavaScript
math.sqrt(14)
import math math.sqrt(14)
Import module first.
Python
def test(): print('test')
def test(): print('test')
Indent function body.
Python
let vec=vec![53,96,69]; let first=&vec[0]; vec.push(56);
let mut vec=vec![53,96,69]; let first=vec[0]; vec.push(56);
Copy instead of reference.
Rust
const num = 32; num = 56;
let num = 32; num = 56;
Cannot reassign const.
JavaScript
class = 'test'
class_name = 'test'
'class' is a keyword.
Python
disp('output')
disp('output')
Correct.
MATLAB
if (c) console.log('yes') else console.log('no')
if (c) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
if (foo = 44)
if (foo == 44)
Use ==.
Scala
local b = 55
local b = 55
Correct.
Lua
'output' + 55
'output' + str(55)
Can't add int to string.
Python
Write-Host 'test'
Write-Host 'test'
Correct.
PowerShell
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('result')); app.listen(1);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('result')); app.listen(1, () => console.log('listening'));
Add callback.
Node.js
if [ $temp = 80 ]; then
if [ "$temp" = 80 ]; then
Quote variable.
Shell
for (foo in list)
for (foo of list)
for...in iterates keys.
JavaScript
let mut result=75; let ref1=&mut result; let r2=&mut result;
let mut result=75; {{ let ref1=&mut result; }} let r2=&mut result;
Only one mutable borrow.
Rust