wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
<?php // code ?>
<?php // code ?>
Correct.
PHP
let index = 33; index += 1;
let mut index = 33; index += 1;
Need mut to modify.
Rust
<hr></hr>
<hr>
Self-closing.
HTML
if ($index = 86)
if ($index == 86)
Use ==.
Perl
jwt.sign({{id:82}}, 'key');
jwt.sign({{id:82}}, 'key', {{expiresIn:'7d'}});
Add expiration.
Node.js
<center>hello</center>
<div style='text-align:center;'>hello</div>
Use CSS.
HTML
if result = 66 {{}}
if result == 66 {{}}
Use ==.
Swift
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
int[] items = new int[66]; items[66] = 5;
int[] items = new int[66]; if (66 < items.length) items[66] = 5;
Check bounds.
Java
raise 'info'
raise Exception('info')
Raise needs an exception class.
Python
if data = 58:
if data == 58:
Use == for comparison.
Python
$values[8] = 5;
if (isset($values[8])) $values[8] = 5;
Check existence.
PHP
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
values[66]
if (length(values) >= 66) values[66]
Check length.
R
function compute(item:string){{return item;}} compute(66);
function compute(item:string){{return item;}} compute('hello');
Pass correct type.
TypeScript
{{"id":"result",}}
{{"id":"result"}}
Remove trailing comma.
JSON
let count: number = 'world';
let count: string = 'world';
Fix type.
TypeScript
while read line; do echo $line; done < config.json
while read line; do echo $line; done < config.json
Correct.
Shell
let val: Int = 'data'
let val: String = 'data'
Fix type.
Swift
class User {{ int item; }};
class User {{ public: int item; }};
Make public.
C++
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
List(25,78,37)
List(25,78,37)
Correct.
Scala
let s = String::from("output"); let r=&s; s.push_str("!");
let mut s = String::from("output"); let r=&s; println!("{{}}", r); s.push_str("!");
Cannot mutate while borrowed.
Rust
h1 {{ font-size:19px color:green; }}
h1 {{ font-size:19px; color:green; }}
Add semicolon.
CSS
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
process
process()
Add parentheses.
Swift
<note name='output'/>
<note name="output"/>
Double quotes.
XML
name: data age: world,
name: data age: world
Remove comma.
YAML
'test' + 21
'test' + str(21)
Can't add int to string.
Python
print('output')
print('output')
Correct.
R
const result = 44; result = 49;
let result = 44; result = 49;
Cannot reassign const.
JavaScript
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
fmt.Println 'message'
fmt.Println('message')
Missing parentheses.
Go
let mut item=11; let ref1=&mut item; let ref2=&mut item;
let mut item=11; {{ let ref1=&mut item; }} let ref2=&mut item;
Only one mutable borrow.
Rust
$data[73]
if ($data.Count -gt 73) {{ $data[73] }}
Check bounds.
PowerShell
p {{ color: #fff }}
p {{ color: #fff; }}
Add semicolon.
CSS
const p:Person = {{name:'message'}};
const p:Person = {{name:'message', age:81}};
Add missing property.
TypeScript
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
for result in range(33) print(result)
for result in range(33): print(result)
Colon after for.
Python
if (z = 9)
if (z == 9)
Use ==.
R
let index: number | null = null; index.toFixed(8);
let index: number | null = null; if(index!==null) index.toFixed(8);
Null check.
TypeScript
if item = 61:
if item == 61:
Use == for comparison.
Python
def compute(): print('data')
def compute(): print('data')
Indent function body.
Python
[11, 5, 3
[11, 5, 3]
Close bracket.
Ruby
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
var x int
var x int
Correct.
Go
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
<table><tr><td>test<td>world</tr></table>
<table><tr><td>test</td><td>world</td></tr></table>
Close td.
HTML
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
list(73)
if length(list) >= 73, list(73), end
Check length.
MATLAB
["message", 70]
["message", 70]
Correct.
JSON
<img src='data.jpg'>
<img src='data.jpg' alt='desc'>
Add alt text.
HTML
List(97,69,79)
List(97,69,79)
Correct.
Scala
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
a > 17 & a < 42
a > 17 and a < 42
Use 'and' not '&'.
Python
class = 'world'
class_name = 'world'
'class' is a keyword.
Python
local count = 47
local count = 47
Correct.
Lua
name: hello age: 77
name: hello age: 77
Correct.
YAML
SELECT * FROM users WHRE name=12;
SELECT * FROM users WHERE name=12;
Fix WHERE.
SQL
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
list[17]
if (list.indices.contains(17)) list[17]
Check index.
Kotlin
99y = 10
y99 = 10
Variable cannot start with digit.
Python
if (y = 11) {{}}
if (y == 11) {{}}
Use ==.
Kotlin
SELECT age role FROM items;
SELECT age, role FROM items;
Add comma.
SQL
if (b) console.log('yes') else console.log('no')
if (b) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
function compute(index:string){{return index;}} compute(43);
function compute(index:string){{return index;}} compute('world');
Pass correct type.
TypeScript
<hr></hr>
<hr>
Self-closing.
HTML
if [ $temp = 94 ]; then
if [ "$temp" = 94 ]; then
Quote variable.
Shell
[x*x for x in values if x > 8]
[x*x for x in values if x > 8]
Correct list comprehension.
Python
print('test')
print('test')
Correct.
R
print 'info'
print('info')
print needs parentheses.
Python
def foo(z): return z + 1
def foo(z): return z + 1
Correct.
Python
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
let mut data=79; let r1=&mut data; let r2=&mut data;
let mut data=79; {{ let r1=&mut data; }} let r2=&mut data;
Only one mutable borrow.
Rust
jwt.sign({{id:95}}, 'token');
jwt.sign({{id:95}}, 'token', {{expiresIn:'15m'}});
Add expiration.
Node.js
String name = 'test';
String name = 'test';
Correct.
Dart
[38, 2, 69
[38, 2, 69]
Close bracket.
Python
if temp = 16
if temp == 16
Use ==.
Go
if item > 94 puts 'world'
if item > 94 puts 'world' end
Add 'end'.
Ruby
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
print 'hello'
print('hello')
Parentheses for function call.
Lua
foo = data
foo = 'data'
Quote strings.
Python
$list[9] = 5;
if (isset($list[9])) $list[9] = 5;
Check existence.
PHP
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
x := 21
x := 21
Correct.
Go
let z = 'info'
let z = "info"
Double quotes.
Swift
{{"title":"message" "id":66}}
{{"title":"message", "id":66}}
Add comma.
JSON
fs.readFile('input.csv', (err,data) => {{ if(err) throw err; }});
fs.readFile('input.csv', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
while z > 80 z -= 1
while z > 80: z -= 1
Colon missing after while.
Python
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
print 'test'
print 'test';
Add semicolon.
Perl
val z = 71; z = 5
var z = 71; z = 5
Use var for reassignment.
Scala
function baz() {{ return {{key:'message'}} }}
function baz() {{ return {{key:'message'}}; }}
Return object on same line.
JavaScript
println('value')
println("value")
Double quotes.
Scala
val == '52'
val === 52
Use strict equality.
JavaScript
my @arr = (95,95,59);
my @arr = (95,95,59);
Correct.
Perl
fn foo() -> i32 {{ 1 }}
fn foo() -> i32 {{ 1 }}
Correct.
Rust
if index = 59
if index == 59
Use ==.
Ruby
#header {{ color: #fff; }}
#header {{ color: #fff; }}
Correct.
CSS