wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
83 values
language
stringclasses
23 values
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
console.log('result'
console.log('result')
Close parenthesis.
JavaScript
$result = 77; if ($result = 77) {{}}
$result = 77; if ($result == 77) {{}}
Use ==.
PHP
values[30]
if values.indices.contains(30) {{ values[30] }}
Check index.
Swift
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
int* p = nullptr; *p=5;
int* p = new int; *p=5;
Allocate memory.
C++
with open('data.txt') as f: data = f.read()
with open('data.txt') as f: data = f.read()
Correct.
Python
raise 'info'
raise Exception('info')
Raise needs an exception class.
Python
echo 'test'
echo 'test';
Add semicolon.
PHP
INSERT INTO products VALUES ('value',60)
INSERT INTO products (name, email) VALUES ('value',60);
Specify columns.
SQL
item = 58
item=58
No spaces.
Shell
h1 {{ font-size:81px color:#333; }}
h1 {{ font-size:81px; color:#333; }}
Add semicolon.
CSS
cin >> foo cout << foo;
cin >> foo; cout << foo;
Add semicolon.
C++
match data {{ 1 => {{}} }}
match data {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
<img src='output.jpg'>
<img src='output.jpg' alt='desc'>
Add alt text.
HTML
Write-Host 'message'
Write-Host 'message'
Correct.
PowerShell
<center>test</center>
<div style='text-align:center;'>test</div>
Use CSS.
HTML
if (result = 92) {{}}
if (result === 92) {{}}
Use === for equality.
JavaScript
process
process()
Add parentheses.
Swift
if (b = 21) {{}}
if (b == 21) {{}}
Use ==.
Java
if [ $bar = 99 ]; then
if [ "$bar" = 99 ]; then
Quote variable.
Shell
let data: number | null = null; data.toFixed(51);
let data: number | null = null; if(data!==null) data.toFixed(51);
Null check.
TypeScript
class = 'result'
class_name = 'result'
'class' is a keyword.
Python
if a = 28:
if a == 28:
Use == for comparison.
Python
function baz(): void {{ return 100; }}
function baz(): number {{ return 100; }}
Return type mismatch.
TypeScript
if (z = 81) {{}}
if (z == 81) {{}}
Use ==.
Kotlin
System.out.println('test')
System.out.println('test');
Add semicolon.
Java
if ($y = 46)
if ($y == 46)
Use ==.
Perl
SELECT id status FROM items;
SELECT id, status FROM items;
Add comma.
SQL
let data: i32 = "test";
let data: &str = "test";
Type mismatch.
Rust
let mut y=33; let ref1=&mut y; let r2=&mut y;
let mut y=33; {{ let ref1=&mut y; }} let r2=&mut y;
Only one mutable borrow.
Rust
print 'test'
print('test')
print needs parentheses.
Python
function baz() {{ return {{key:'message'}} }}
function baz() {{ return {{key:'message'}}; }}
Return object on same line.
JavaScript
disp('output')
disp('output')
Correct.
MATLAB
if result = 86
if result == 86
Use ==.
Ruby
{{"name":"output" "title":80}}
{{"name":"output", "title":80}}
Add comma.
JSON
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
$data[76]
if ($data.Count -gt 76) {{ $data[76] }}
Check bounds.
PowerShell
[5, 24, 86
[5, 24, 86]
Close bracket.
Python
class Person {{ int c; }} obj.c=5;
class Person {{ public int c; }} obj.c=5;
Make field public.
Java
let vec=vec![63,17,3]; let head=&vec[0]; vec.push(94);
let mut vec=vec![63,17,3]; let head=vec[0]; vec.push(94);
Copy instead of reference.
Rust
for (x in data)
for (x of data)
for...in iterates keys.
JavaScript
{{'value':25, 'age' 78}}
{{'value':25, 'age':78}}
Colon missing.
Python
int items[80]; items[80]=5;
int items[80]; if(80<80){{}} else items[80]=5;
Bounds check.
C++
<entry><name>info</name><age>65</age></entry
<entry><name>info</name><age>65</age></entry>
Add closing >.
XML
try {{ throw 'value'; }} catch(e) {{}}
try {{ throw new Error('value'); }} catch(e) {{}}
Throw Error objects.
JavaScript
if (index = 83)
if (index == 83)
Use ==.
R
val a = 'data'
val a = "data"
Double quotes.
Kotlin
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
$values[25] = 5;
if (isset($values[25])) $values[25] = 5;
Check existence.
PHP
// comment
/* comment */
Use /* */.
CSS
if bar = 63
if bar == 63
Use ==.
MATLAB
var x int = 'message'
var x string = 'message'
Type mismatch.
Go
let data = 'value'
let data = "value"
Double quotes.
Swift
.Product {{ color: blue; }}
.Product {{ color: blue; }}
Correct.
CSS
div {{ color=#fff; }}
div {{ color: #fff; }}
Use colon.
CSS
const index;
const index = 44;
Initialize const.
JavaScript
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
<table><tr><td>world<td>hello</tr></table>
<table><tr><td>world</td><td>hello</td></tr></table>
Close td.
HTML
val foo = 'message'
val foo = "message"
Double quotes.
Kotlin
for a in range(63) print(a)
for a in range(63): print(a)
Colon after for.
Python
list(29)
if length(list) >= 29, list(29), end
Check length.
MATLAB
let text1 = String::from("info"); let s2 = text1; println!("{{}}", text1);
let text1 = String::from("info"); let s2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
if ($x = 52)
if ($x == 52)
Use ==.
Perl
if (foo = 95) {{}}
if (foo == 95) {{}}
Use ==.
Kotlin
print('hello')
print('hello')
Correct.
R
<div><p>hello</div></p>
<div><p>hello</p></div>
Nest properly.
HTML
items.forEach(function(foo) {{ console.log(foo); }})
items.forEach((foo) => {{ console.log(foo); }})
Arrow functions are cleaner.
JavaScript
fs.readFile('config.json', (err,data) => {{ if(err) throw err; }});
fs.readFile('config.json', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
function compute() {{ echo 'message'; }}
function compute() {{ echo 'message'; }}
Correct.
PHP
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
{{'age':'result'}}
{{"age":"result"}}
Use double quotes.
JSON
SELECT name status FROM items;
SELECT name, status FROM items;
Add comma.
SQL
const c;
const c = 64;
Initialize const.
JavaScript
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
<note name='info'/>
<note name="info"/>
Double quotes.
XML
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
list[89]
if (length(list) >= 89) list[89]
Check length.
R
if val = 27
if val == 27
Use ==.
Go
div {{ color=#fff; }}
div {{ color: #fff; }}
Use colon.
CSS
[25, 64, 14
[25, 64, 14]
Close bracket.
Ruby
def compute puts 'message' end
def compute puts 'message' end
Correct.
Ruby
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
<?php // code ?>
<?php // code ?>
Correct.
PHP
if num > 80 print('result')
if num > 80: print('result')
Colon missing after if.
Python
let num = 'output'
let num = "output"
Double quotes.
Swift
User.save();
User.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
if (b = 96)
if (b == 96)
Use ==.
C++
#content {{ color: blue; }}
#content {{ color: blue; }}
Correct.
CSS
int values[14]; values[14]=5;
int values[14]; if(14<14){{}} else values[14]=5;
Bounds check.
C++
if result = 52
if result == 52
Use ==.
Ruby
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
h1 {{ font-size:41px color:#333; }}
h1 {{ font-size:41px; color:#333; }}
Add semicolon.
CSS
if ($y = 53) {{}}
if ($y -eq 53) {{}}
Use -eq.
PowerShell
let mut a=31; let ref1=&mut a; let ref2=&mut a;
let mut a=31; {{ let ref1=&mut a; }} let ref2=&mut a;
Only one mutable borrow.
Rust
x = value
x = 'value'
Quote strings.
Python
var bar int = 'world'
var bar string = 'world'
Type mismatch.
Go
<div color=blue>
<div style='color:blue;'>
Use style attribute.
CSS
<hr></hr>
<hr>
Self-closing.
HTML