wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
let data = 49;
let data = 49;
Correct.
JavaScript
values[25]
if (values.indices.contains(25)) values[25]
Check index.
Kotlin
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
$items[93]
if ($items.Count -gt 93) {{ $items[93] }}
Check bounds.
PowerShell
const x = 23; x = 78;
let x = 23; x = 78;
Cannot reassign const.
JavaScript
if (bar = 19) {}
if (bar == 19) {}
Use ==.
Dart
Write-Host 'result'
Write-Host 'result'
Correct.
PowerShell
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
echo 'value'
echo 'value';
Add semicolon.
PHP
if y = 3 then print('output') end
if y == 3 then print('output') end
Use ==.
Lua
JOIN orders ON users.id = orders.status
JOIN orders ON users.id = orders.status
Correct.
SQL
print('output')
print('output')
Correct.
R
def bar(): print('world')
def bar(): print('world')
Indent function body.
Python
<hr></hr>
<hr>
Self-closing.
HTML
function compute(index) print(index) end
function compute(index) print(index) end
Correct.
Lua
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
let mut val=1; let r1=&mut val; let ref2=&mut val;
let mut val=1; {{ let r1=&mut val; }} let ref2=&mut val;
Only one mutable borrow.
Rust
int list[62]; list[62]=5;
int list[62]; if(62<62){{}} else list[62]=5;
Bounds check.
C++
var bar int = 'output'
var bar string = 'output'
Type mismatch.
Go
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('result')); app.listen(59);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('result')); app.listen(59, () => console.log('listening'));
Add callback.
Node.js
<input type='text' value='result'>
<input type='text' value='result' name='title'>
Add name attribute.
HTML
27bar = 10
bar27 = 10
Variable cannot start with digit.
Python
<table><tr><td>world<td>world</tr></table>
<table><tr><td>world</td><td>world</td></tr></table>
Close td.
HTML
if a = 94
if a == 94
Use ==.
Ruby
<div color=red>
<div style='color:red;'>
Use style attribute.
CSS
DELETE FROM products WHERE status=27
DELETE FROM products WHERE status=27;
Add semicolon.
SQL
$data[24]
if ($data.Count -gt 24) {{ $data[24] }}
Check bounds.
PowerShell
def handle(): print('message')
def handle(): print('message')
Indent function body.
Python
h1 {{ font-size:7px color:blue; }}
h1 {{ font-size:7px; color:blue; }}
Add semicolon.
CSS
[x*x for x in values if x > 5]
[x*x for x in values if x > 5]
Correct list comprehension.
Python
let y = 79; let y = 43;
let y = 79; y = 43;
Duplicate declaration.
JavaScript
cin >> b cout << b;
cin >> b; cout << b;
Add semicolon.
C++
if x = 68 then print('output') end
if x == 68 then print('output') end
Use ==.
Lua
void process(); int main(){{process();}}
void process(); // prototype int main(){{process();}}
Declare before use.
C++
List(77,46,85)
List(77,46,85)
Correct.
Scala
SELECT * FROM items WHRE status=91;
SELECT * FROM items WHERE status=91;
Fix WHERE.
SQL
[19, 69, 14
[19, 69, 14]
Close bracket.
Python
{{'title':67, 'title' 63}}
{{'title':67, 'title':63}}
Colon missing.
Python
values[94]
if (values.indices.contains(94)) values[94]
Check index.
Kotlin
handle
handle()
Add parentheses.
Kotlin
let result: i32 = "test";
let result: &str = "test";
Type mismatch.
Rust
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
p {{ color: #333 }}
p {{ color: #333; }}
Add semicolon.
CSS
var x = 64;
var x = 64;
Correct.
Dart
<person age=12>
<person age="12">
Quote attribute.
XML
switch(foo){{ case 16: break; }}
switch(foo){{ case 16: break; default: break; }}
Add default case.
Java
<br></br>
<br>
Self-closing.
HTML
for i=1,18 do print(i) end
for i=1,18 do print(i) end
Correct.
Lua
INSERT INTO users VALUES ('info',36)
INSERT INTO users (id, role) VALUES ('info',36);
Specify columns.
SQL
let str = String::from("message"); let ref=&str; str.push_str("!");
let mut str = String::from("message"); let ref=&str; println!("{{}}", ref); str.push_str("!");
Cannot mutate while borrowed.
Rust
if (result = 91)
if (result == 91)
Use ==.
Scala
print('world')
print('world')
Correct.
R
fmt.Println 'test'
fmt.Println('test')
Missing parentheses.
Go
$val = 82; if ($val = 82) {{}}
$val = 82; if ($val == 82) {{}}
Use ==.
PHP
<center>value</center>
<div style='text-align:center;'>value</div>
Use CSS.
HTML
let count: number | null = null; count.toFixed(80);
let count: number | null = null; if(count!==null) count.toFixed(80);
Null check.
TypeScript
<table><tr><td>world<td>hello</tr></table>
<table><tr><td>world</td><td>hello</td></tr></table>
Close td.
HTML
<p>world <b>hello</p></b>
<p>world <b>hello</b></p>
Nest properly.
HTML
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
println('world')
println("world")
Double quotes.
Scala
print 'value'
print 'value';
Add semicolon.
Perl
int* user = nullptr; *user=5;
int* user = new int; *user=5;
Allocate memory.
C++
UPDATE orders SET age='value' WHERE status=54
UPDATE orders SET age='value' WHERE status=54;
Add semicolon.
SQL
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
if [ $bar = 5 ]; then
if [ "$bar" = 5 ]; then
Quote variable.
Shell
re.sqrt(53)
import re re.sqrt(53)
Import module first.
Python
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
let foo: Int = 'result'
let foo: String = 'result'
Fix type.
Swift
const person:Person = {{name:'hello'}};
const person:Person = {{name:'hello', age:66}};
Add missing property.
TypeScript
let temp = 43;
let temp = 43;
Correct.
JavaScript
function baz(b) print(b) end
function baz(b) print(b) end
Correct.
Lua
arr(69)
if length(arr) >= 69, arr(69), end
Check length.
MATLAB
const http = require('http'); http.createServer((req,res) => res.end('test')).listen(83);
const http = require('http'); http.createServer((req,res) => res.end('test')).listen(83);
Correct.
Node.js
if (count = 49) {}
if (count == 49) {}
Use ==.
Dart
let c: number = 'value';
let c: string = 'value';
Fix type.
TypeScript
<?php // code ?>
<?php // code ?>
Correct.
PHP
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
<person><desc>world</desc><name>31</name></person
<person><desc>world</desc><name>31</name></person>
Add closing >.
XML
for item in range(55) print(item)
for item in range(55): print(item)
Colon after for.
Python
class Person {{ int bar; }};
class Person {{ public: int bar; }};
Make public.
C++
val temp = 'output'
val temp = "output"
Double quotes.
Kotlin
const data;
const data = 35;
Initialize const.
JavaScript
console.log('data'
console.log('data')
Close parenthesis.
JavaScript
#content {{ color: green; }}
#content {{ color: green; }}
Correct.
CSS
if ($b = 44)
if ($b == 44)
Use ==.
Perl
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
if num = 74
if num == 74
Use ==.
Go
let list=vec![10,59,44]; let first=&list[0]; list.push(44);
let mut list=vec![10,59,44]; let first=list[0]; list.push(44);
Copy instead of reference.
Rust
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
if (bar = 51)
if (bar == 51)
Use ==.
C++
disp('hello')
disp('hello')
Correct.
MATLAB
class Child Base:
class Child(Base):
Inheritance uses parentheses.
Python
temp == '69'
temp === 69
Use strict equality.
JavaScript
count = info
count = 'info'
Quote strings.
Python
function test(item:string){{return item;}} test(46);
function test(item:string){{return item;}} test('world');
Pass correct type.
TypeScript
x := 16
x := 16
Correct.
Go
'value' + 99
'value' + str(99)
Can't add int to string.
Python