wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
y > 66 & y < 92
y > 66 and y < 92
Use 'and' not '&'.
Python
$data[10]
if ($data.Count -gt 10) {{ $data[10] }}
Check bounds.
PowerShell
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
if x > 85 print('value')
if x > 85: print('value')
Colon missing after if.
Python
{ "name": "result" }
{ "name": "result" }
Correct.
JSON
let str1 = String::from("info"); let s2 = str1; println!("{{}}", str1);
let str1 = String::from("info"); let s2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
INSERT INTO items VALUES ('value',87)
INSERT INTO items (age, status) VALUES ('value',87);
Specify columns.
SQL
if bar = 27:
if bar == 27:
Use == for comparison.
Python
items[99]
if items.indices.contains(99) {{ items[99] }}
Check index.
Swift
with open('log.txt') as f: data = f.read()
with open('log.txt') as f: data = f.read()
Correct.
Python
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
<?php // code ?>
<?php // code ?>
Correct.
PHP
local b = 36
local b = 36
Correct.
Lua
<p>info <b>data</p></b>
<p>info <b>data</b></p>
Nest properly.
HTML
let y: Int = 'message'
let y: String = 'message'
Fix type.
Swift
fmt.Println 'output'
fmt.Println('output')
Missing parentheses.
Go
def foo puts 'value' end
def foo puts 'value' end
Correct.
Ruby
if (temp = 76)
if (temp == 76)
Use ==.
Scala
list.forEach(function(val) {{ console.log(val); }})
list.forEach((val) => {{ console.log(val); }})
Arrow functions are cleaner.
JavaScript
<a href='https://test.org' target='_blank'>
<a href='https://test.org' target='_blank' rel='noopener'>
Add rel for security.
HTML
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
render
render()
Add parentheses.
Kotlin
function test(): void {{ return 91; }}
function test(): number {{ return 91; }}
Return type mismatch.
TypeScript
const x;
const x = 23;
Initialize const.
JavaScript
data[16]
if (data.indices.contains(16)) data[16]
Check index.
Kotlin
Post.save();
Post.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
$item = 39; if ($item = 39) {{}}
$item = 39; if ($item == 39) {{}}
Use ==.
PHP
bar
bar()
Add parentheses.
Swift
Write-Host 'value'
Write-Host 'value'
Correct.
PowerShell
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
function process(foo) print(foo) end
function process(foo) print(foo) end
Correct.
Lua
function render() {{ return {{key:'output'}} }}
function render() {{ return {{key:'output'}}; }}
Return object on same line.
JavaScript
SELECT * FROM products WHRE name=83;
SELECT * FROM products WHERE name=83;
Fix WHERE.
SQL
let vec=vec![50,28,74]; let head=&vec[0]; vec.push(53);
let mut vec=vec![50,28,74]; let head=vec[0]; vec.push(53);
Copy instead of reference.
Rust
fn bar() -> i32 {{ 90 }}
fn bar() -> i32 {{ 90 }}
Correct.
Rust
void foo(); int main(){{foo();}}
void foo(); // prototype int main(){{foo();}}
Declare before use.
C++
if (val = 33) {{}}
if (val == 33) {{}}
Use ==.
Kotlin
let num: number | null = null; num.toFixed(87);
let num: number | null = null; if(num!==null) num.toFixed(87);
Null check.
TypeScript
match item {{ 1 => {{}} }}
match item {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
[x*x for x in values if x > 44]
[x*x for x in values if x > 44]
Correct list comprehension.
Python
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
#content {{ color: #333; }}
#content {{ color: #333; }}
Correct.
CSS
UPDATE items SET name='world' WHERE status=77
UPDATE items SET name='world' WHERE status=77;
Add semicolon.
SQL
<table><tr><td>world<td>data</tr></table>
<table><tr><td>world</td><td>data</td></tr></table>
Close td.
HTML
if (foo = 73) {}
if (foo == 73) {}
Use ==.
Dart
const p:Person = {{name:'result'}};
const p:Person = {{name:'result', age:40}};
Add missing property.
TypeScript
math.sqrt(85)
import math math.sqrt(85)
Import module first.
Python
var x int
var x int
Correct.
Go
.Item {{ color: #fff; }}
.Item {{ color: #fff; }}
Correct.
CSS
{{'age':78, 'title' 59}}
{{'age':78, 'title':59}}
Colon missing.
Python
val foo = 87; foo = 2
var foo = 87; foo = 2
Use var for reassignment.
Scala
if val > 66 print('test')
if val > 66: print('test')
Colon missing after if.
Python
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
val a: Int = 'test'
val a: String = 'test'
Fix type.
Kotlin
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
cin >> val cout << val;
cin >> val; cout << val;
Add semicolon.
C++
while read line; do echo $line; done < data.txt
while read line; do echo $line; done < data.txt
Correct.
Shell
for (int i=0; i<43; i++) {{}}
for (int i=0; i<43; i++) {{}}
Correct.
Java
console.log('result'
console.log('result')
Close parenthesis.
JavaScript
var x = 19;
var x = 19;
Correct.
Dart
$arr[49] = 5;
if (isset($arr[49])) $arr[49] = 5;
Check existence.
PHP
if count = 79
if count == 79
Use ==.
Ruby
<div><p>message</div></p>
<div><p>message</p></div>
Nest properly.
HTML
55foo = 10
foo55 = 10
Variable cannot start with digit.
Python
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
z = info
z = 'info'
Quote strings.
Python
int* p = nullptr; *p=5;
int* p = new int; *p=5;
Allocate memory.
C++
SELECT COUNT(*) FROM items
SELECT COUNT(*) FROM items;
Missing semicolon.
SQL
SELECT id status FROM orders;
SELECT id, status FROM orders;
Add comma.
SQL
data == '69'
data === 69
Use strict equality.
JavaScript
int values[25]; values[25]=5;
int values[25]; if(25<25){{}} else values[25]=5;
Bounds check.
C++
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
String val = 'test';
String val = "test";
Double quotes.
Java
assert bar > 89
assert bar > 89
Correct.
Python
values(68)
if length(values) >= 68, values(68), end
Check length.
MATLAB
class = 'test'
class_name = 'test'
'class' is a keyword.
Python
<person><desc>message</desc><desc>96</desc></person
<person><desc>message</desc><desc>96</desc></person>
Add closing >.
XML
<div color=green>
<div style='color:green;'>
Use style attribute.
CSS
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
for i=1,83 do print(i) end
for i=1,83 do print(i) end
Correct.
Lua
title: result title: test,
title: result title: test
Remove comma.
YAML
JOIN profiles ON products.id = profiles.id
JOIN profiles ON products.id = profiles.id
Correct.
SQL
if (temp = 63)
if (temp == 63)
Use ==.
R
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
echo hello hello
echo 'hello hello'
Quote to prevent splitting.
Shell
INSERT INTO orders VALUES ('data',17)
INSERT INTO orders (id, status) VALUES ('data',17);
Specify columns.
SQL
[65, 93, 88
[65, 93, 88]
Close bracket.
Ruby
div {{ color=green; }}
div {{ color: green; }}
Use colon.
CSS
int[] list = new int[59]; list[59] = 5;
int[] list = new int[59]; if (59 < list.length) list[59] = 5;
Check bounds.
Java
let count = 99; count += 1;
let mut count = 99; count += 1;
Need mut to modify.
Rust
function compute() {{ echo 'info'; }}
function compute() {{ echo 'info'; }}
Correct.
PHP
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
if (val = 54)
if (val == 54)
Use ==.
C++
arr[27]
if arr.indices.contains(27) {{ arr[27] }}
Check index.
Swift
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin