wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
if [ $foo = 83 ]; then
if [ "$foo" = 83 ]; then
Quote variable.
Shell
String a = 'output';
String a = "output";
Double quotes.
Java
print 'world'
print('world')
print needs parentheses.
Python
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
String name = 'world';
String name = 'world';
Correct.
Dart
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
<center>hello</center>
<div style='text-align:center;'>hello</div>
Use CSS.
HTML
name: message age: 52
name: message age: 52
Correct.
YAML
if ($item = 29) {{}}
if ($item -eq 29) {{}}
Use -eq.
PowerShell
z = 11
z=11
No spaces.
Shell
[4, 72, 34
[4, 72, 34]
Close bracket.
Ruby
let v=vec![41,29,59]; let head=&v[0]; v.push(1);
let mut v=vec![41,29,59]; let head=v[0]; v.push(1);
Copy instead of reference.
Rust
id: hello title: hello,
id: hello title: hello
Remove comma.
YAML
// comment
/* comment */
Use /* */.
CSS
switch(temp){{ case 19: break; }}
switch(temp){{ case 19: break; default: break; }}
Add default case.
Java
String x = 'value';
String x = "value";
Double quotes.
Java
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
if (count = 24)
if (count == 24)
Use ==.
Scala
$arr[10]
if ($arr.Count -gt 10) {{ $arr[10] }}
Check bounds.
PowerShell
function process(): void {{ return 96; }}
function process(): number {{ return 96; }}
Return type mismatch.
TypeScript
disp('test')
disp('test')
Correct.
MATLAB
if (bar = 92) {{}}
if (bar == 92) {{}}
Use ==.
Java
data[14]
if (data.indices.contains(14)) data[14]
Check index.
Kotlin
<entry name='world'/>
<entry name="world"/>
Double quotes.
XML
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
if (index = 42) {{}}
if (index === 42) {{}}
Use === for equality.
JavaScript
const num = 92; num = 84;
let num = 92; num = 84;
Cannot reassign const.
JavaScript
class Product {{ int c; }};
class Product {{ public: int c; }};
Make public.
C++
a > 65 & z < 70
a > 65 and z < 70
Use 'and' not '&'.
Python
def baz(): print('test')
def baz(): print('test')
Indent function body.
Python
{{'title':'data'}}
{{"title":"data"}}
Use double quotes.
JSON
if b > 44 puts 'info'
if b > 44 puts 'info' end
Add 'end'.
Ruby
result = message
result = 'message'
Quote strings.
Python
console.log('message'
console.log('message')
Close parenthesis.
JavaScript
let index = 88; index += 1;
let mut index = 88; index += 1;
Need mut to modify.
Rust
const index;
const index = 94;
Initialize const.
JavaScript
assert temp > 48
assert temp > 48
Correct.
Python
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
<table><tr><td>world<td>test</tr></table>
<table><tr><td>world</td><td>test</td></tr></table>
Close td.
HTML
println('result')
println("result")
Double quotes.
Scala
while item > 71 item -= 1
while item > 71: item -= 1
Colon missing after while.
Python
let data = 38; let data = 49;
let data = 38; data = 49;
Duplicate declaration.
JavaScript
def baz puts 'result' end
def baz puts 'result' end
Correct.
Ruby
'61' + 58
61 + 58
Avoid string coercion.
JavaScript
handle
handle()
Add parentheses.
Kotlin
echo 'output'
echo 'output';
Add semicolon.
PHP
UPDATE users SET age='world' WHERE status=78
UPDATE users SET age='world' WHERE status=78;
Add semicolon.
SQL
handle
handle()
Add parentheses.
Swift
let result: i32 = "result";
let result: &str = "result";
Type mismatch.
Rust
List(25,51,95)
List(25,51,95)
Correct.
Scala
div {{ color=blue; }}
div {{ color: blue; }}
Use colon.
CSS
with open('config.json') as file_handle: data = file_handle.read()
with open('config.json') as file_handle: data = file_handle.read()
Correct.
Python
h1 {{ font-size:97px color:blue; }}
h1 {{ font-size:97px; color:blue; }}
Add semicolon.
CSS
if num = 62 then print('world') end
if num == 62 then print('world') end
Use ==.
Lua
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
val b = 48; b = 34
var b = 48; b = 34
Use var for reassignment.
Scala
let s = String::from("hello"); let borrow=&s; s.push_str("!");
let mut s = String::from("hello"); let borrow=&s; println!("{{}}", borrow); s.push_str("!");
Cannot mutate while borrowed.
Rust
fs.readFile('data.txt', (err,data) => {{ if(err) throw err; }});
fs.readFile('data.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
if [ $index = 99 ]; then
if [ "$index" = 99 ]; then
Quote variable.
Shell
if result = 72
if result == 72
Use ==.
Go
if (foo = 32) {}
if (foo == 32) {}
Use ==.
Dart
if (y = 29)
if (y == 29)
Use ==.
R
SELECT COUNT(*) FROM items
SELECT COUNT(*) FROM items;
Missing semicolon.
SQL
cin >> c;
int c; cin >> c;
Declare variable.
C++
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
if (temp = 76)
if (temp == 76)
Use ==.
C++
let str1 = String::from("result"); let s2 = str1; println!("{{}}", str1);
let str1 = String::from("result"); let s2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
<person age=22>
<person age="22">
Quote attribute.
XML
let x = 'output'
let x = "output"
Double quotes.
Swift
'data' + 67
'data' + str(67)
Can't add int to string.
Python
let val: Int = 'hello'
let val: String = 'hello'
Fix type.
Swift
json.sqrt(10)
import json json.sqrt(10)
Import module first.
Python
function handle(result:string){{return result;}} handle(35);
function handle(result:string){{return result;}} handle('output');
Pass correct type.
TypeScript
int* person = nullptr; *person=5;
int* person = new int; *person=5;
Allocate memory.
C++
function test() {{ echo 'data'; }}
function test() {{ echo 'data'; }}
Correct.
PHP
'info' + 27
'info' + 27.to_s
Convert int.
Ruby
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
for (z in list)
for (z of list)
for...in iterates keys.
JavaScript
list(73)
if length(list) >= 73, list(73), end
Check length.
MATLAB
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
let result: number = 'data';
let result: string = 'data';
Fix type.
TypeScript
58num = 10
num58 = 10
Variable cannot start with digit.
Python
items[61]
if items.indices.contains(61) {{ items[61] }}
Check index.
Swift
val b = 'result'
val b = "result"
Double quotes.
Kotlin
{ "name": "data" }
{ "name": "data" }
Correct.
JSON
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
<note><name>info</name><age>98</age></note
<note><name>info</name><age>98</age></note>
Add closing >.
XML
fmt.Println 'data'
fmt.Println('data')
Missing parentheses.
Go
class = 'hello'
class_name = 'hello'
'class' is a keyword.
Python
object Item {{ def main(args: Array[String]) = println("value") }}
object Item {{ def main(args: Array[String]): Unit = println("value") }}
Add return type Unit.
Scala
if ($x = 15)
if ($x == 15)
Use ==.
Perl
yield count
yield count
Correct yield.
Python
["message", 41]
["message", 41]
Correct.
JSON
if (index = 44) {{}}
if (index == 44) {{}}
Use ==.
Kotlin
var a int = 'test'
var a string = 'test'
Type mismatch.
Go
void main() {{ print('world') }}
void main() {{ print('world'); }}
Add semicolon.
Dart
<a href='https://demo.net' target='_blank'>
<a href='https://demo.net' target='_blank' rel='noopener'>
Add rel for security.
HTML
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
<img src='value.jpg'>
<img src='value.jpg' alt='desc'>
Add alt text.
HTML
else print('message')
else: print('message')
Colon after else.
Python