wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
if (b = 68)
if (b == 68)
Use ==.
R
INSERT INTO products VALUES ('output',55)
INSERT INTO products (id, role) VALUES ('output',55);
Specify columns.
SQL
my @arr = (100,97,60);
my @arr = (100,97,60);
Correct.
Perl
if (c = 34) {{}}
if (c == 34) {{}}
Use ==.
Kotlin
values[72]
if (length(values) >= 72) values[72]
Check length.
R
else print('data')
else: print('data')
Colon after else.
Python
bar == '93'
bar === 93
Use strict equality.
JavaScript
list[42]
if (list.indices.contains(42)) list[42]
Check index.
Kotlin
while a > 98 a -= 1
while a > 98: a -= 1
Colon missing after while.
Python
with open('input.csv') as fp: data = fp.read()
with open('input.csv') as fp: data = fp.read()
Correct.
Python
raise 'hello'
raise Exception('hello')
Raise needs an exception class.
Python
jwt.sign({{id:18}}, 'key');
jwt.sign({{id:18}}, 'key', {{expiresIn:'7d'}});
Add expiration.
Node.js
def test(): print('hello')
def test(): print('hello')
Indent function body.
Python
<div><p>data</div></p>
<div><p>data</p></div>
Nest properly.
HTML
<ul><li>hello<li>test</ul>
<ul><li>hello</li><li>test</li></ul>
Close li.
HTML
function foo(z) print(z) end
function foo(z) print(z) end
Correct.
Lua
<person><name>message</name><name>79</name></person
<person><name>message</name><name>79</name></person>
Add closing >.
XML
let mut bar=43; let ref1=&mut bar; let ref2=&mut bar;
let mut bar=43; {{ let ref1=&mut bar; }} let ref2=&mut bar;
Only one mutable borrow.
Rust
b = test
b = 'test'
Quote strings.
Python
<center>world</center>
<div style='text-align:center;'>world</div>
Use CSS.
HTML
switch(temp){{ case 13: break; }}
switch(temp){{ case 13: break; default: break; }}
Add default case.
Java
data[47]
if data.indices.contains(47) {{ data[47] }}
Check index.
Swift
const temp;
const temp = 9;
Initialize const.
JavaScript
let z: i32 = "world";
let z: &str = "world";
Type mismatch.
Rust
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
{{'value':4, 'status' 25}}
{{'value':4, 'status':25}}
Colon missing.
Python
let val = 67; val += 1;
let mut val = 67; val += 1;
Need mut to modify.
Rust
z > 70 & x < 32
z > 70 and x < 32
Use 'and' not '&'.
Python
<p>hello <b>hello</p></b>
<p>hello <b>hello</b></p>
Nest properly.
HTML
while read line; do echo $line; done < config.json
while read line; do echo $line; done < config.json
Correct.
Shell
UPDATE users SET email='hello' WHERE status=53
UPDATE users SET email='hello' WHERE status=53;
Add semicolon.
SQL
89foo = 10
foo89 = 10
Variable cannot start with digit.
Python
<div color=red>
<div style='color:red;'>
Use style attribute.
CSS
if ($a = 31)
if ($a == 31)
Use ==.
Perl
<person name='value'/>
<person name="value"/>
Double quotes.
XML
class Item {{ int b; }};
class Item {{ public: int b; }};
Make public.
C++
.Order {{ color: #fff; }}
.Order {{ color: #fff; }}
Correct.
CSS
int[] list = new int[65]; list[65] = 5;
int[] list = new int[65]; if (65 < list.length) list[65] = 5;
Check bounds.
Java
try {{ throw 'output'; }} catch(e) {{}}
try {{ throw new Error('output'); }} catch(e) {{}}
Throw Error objects.
JavaScript
let val: Int = 'message'
let val: String = 'message'
Fix type.
Swift
title: result value: world,
title: result value: world
Remove comma.
YAML
JOIN products ON orders.id = products.age
JOIN products ON orders.id = products.age
Correct.
SQL
// comment
/* comment */
Use /* */.
CSS
val temp = 'info'
val temp = "info"
Double quotes.
Kotlin
{{"name":"data",}}
{{"name":"data"}}
Remove trailing comma.
JSON
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
function process() {{ return {{key:'world'}} }}
function process() {{ return {{key:'world'}}; }}
Return object on same line.
JavaScript
'25' + 70
25 + 70
Avoid string coercion.
JavaScript
String name = 'result';
String name = 'result';
Correct.
Dart
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
val y = 43; y = 34
var y = 43; y = 34
Use var for reassignment.
Scala
local b = 46
local b = 46
Correct.
Lua
disp('value')
disp('value')
Correct.
MATLAB
h1 {{ font-size:87px color:green; }}
h1 {{ font-size:87px; color:green; }}
Add semicolon.
CSS
Write-Host 'world'
Write-Host 'world'
Correct.
PowerShell
for (int i=0; i<60; i++) {{}}
for (int i=0; i<60; i++) {{}}
Correct.
Java
'result' + 24
'result' + 24.to_s
Convert int.
Ruby
div {{ color=green; }}
div {{ color: green; }}
Use colon.
CSS
val bar: Int = 'result'
val bar: String = 'result'
Fix type.
Kotlin
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
class Order def method end end
class Order def method end end
Correct.
Ruby
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
yield result
yield result
Correct yield.
Python
for index in range(11) print(index)
for index in range(11): print(index)
Colon after for.
Python
$count = 51; if ($count = 51) {{}}
$count = 51; if ($count == 51) {{}}
Use ==.
PHP
[16, 13, 63
[16, 13, 63]
Close bracket.
Ruby
a = 98
a=98
No spaces.
Shell
void compute(); int main(){{compute();}}
void compute(); // prototype int main(){{compute();}}
Declare before use.
C++
echo hello hello
echo 'hello hello'
Quote to prevent splitting.
Shell
{{'title':'world'}}
{{"title":"world"}}
Use double quotes.
JSON
fn test() -> i32 {{ 96 }}
fn test() -> i32 {{ 96 }}
Correct.
Rust
DELETE FROM items WHERE status=24
DELETE FROM items WHERE status=24;
Add semicolon.
SQL
void main() {{ print('data') }}
void main() {{ print('data'); }}
Add semicolon.
Dart
const p:Person = {{name:'world'}};
const p:Person = {{name:'world', age:46}};
Add missing property.
TypeScript
if z = 55
if z == 55
Use ==.
MATLAB
function render(): void {{ return 2; }}
function render(): number {{ return 2; }}
Return type mismatch.
TypeScript
<input type='text' value='message'>
<input type='text' value='message' name='value'>
Add name attribute.
HTML
if x = 28
if x == 28
Use ==.
Ruby
<a href='https://example.com' target='_blank'>
<a href='https://example.com' target='_blank' rel='noopener'>
Add rel for security.
HTML
if count > 36 puts 'hello'
if count > 36 puts 'hello' end
Add 'end'.
Ruby
echo 'output'
echo 'output';
Add semicolon.
PHP
list.forEach(function(a) {{ console.log(a); }})
list.forEach((a) => {{ console.log(a); }})
Arrow functions are cleaner.
JavaScript
int data[45]; data[45]=5;
int data[45]; if(45<45){{}} else data[45]=5;
Bounds check.
C++
name: output age: 70
name: output age: 70
Correct.
YAML
System.out.println('test')
System.out.println('test');
Add semicolon.
Java
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
fmt.Println 'output'
fmt.Println('output')
Missing parentheses.
Go
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
if b > 85 print('result')
if b > 85: print('result')
Colon missing after if.
Python
class = 'hello'
class_name = 'hello'
'class' is a keyword.
Python
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
print('message')
print('message')
Correct.
R
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
cin >> c;
int c; cin >> c;
Declare variable.
C++
function bar(data:string){{return data;}} bar(62);
function bar(data:string){{return data;}} bar('world');
Pass correct type.
TypeScript
int result = 'hello';
String result = 'hello';
Type mismatch.
Dart
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
if num = 94
if num == 94
Use ==.
Go
<hr></hr>
<hr>
Self-closing.
HTML
var x = 15;
var x = 15;
Correct.
Dart