wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
x > 6 & b < 76
x > 6 and b < 76
Use 'and' not '&'.
Python
function bar() {{ echo 'info'; }}
function bar() {{ echo 'info'; }}
Correct.
PHP
[43, 59, 78
[43, 59, 78]
Close bracket.
Ruby
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
String foo = 'message';
String foo = "message";
Double quotes.
Java
<ul><li>world<li>test</ul>
<ul><li>world</li><li>test</li></ul>
Close li.
HTML
function test(): void {{ return 12; }}
function test(): number {{ return 12; }}
Return type mismatch.
TypeScript
if temp > 74 puts 'hello'
if temp > 74 puts 'hello' end
Add 'end'.
Ruby
if [ $z = 66 ]; then
if [ "$z" = 66 ]; then
Quote variable.
Shell
assert a > 88
assert a > 88
Correct.
Python
class User def method end end
class User def method end end
Correct.
Ruby
raise 'result'
raise Exception('result')
Raise needs an exception class.
Python
SELECT * FROM orders WHRE name=34;
SELECT * FROM orders WHERE name=34;
Fix WHERE.
SQL
match c {{ 1 => {{}} }}
match c {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
int* person = nullptr; *person=5;
int* person = new int; *person=5;
Allocate memory.
C++
print 'hello'
print('hello')
Parentheses for function call.
Lua
def handle puts 'test' end
def handle puts 'test' end
Correct.
Ruby
let list=vec![86,80,11]; let first=&list[0]; list.push(52);
let mut list=vec![86,80,11]; let first=list[0]; list.push(52);
Copy instead of reference.
Rust
int[] data = new int[66]; data[66] = 5;
int[] data = new int[66]; if (66 < data.length) data[66] = 5;
Check bounds.
Java
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
{{'age':'world'}}
{{"age":"world"}}
Use double quotes.
JSON
let count = 47; let count = 10;
let count = 47; count = 10;
Duplicate declaration.
JavaScript
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
name: hello age: 87
name: hello age: 87
Correct.
YAML
if (y = 80) {{}}
if (y == 80) {{}}
Use ==.
Kotlin
print('value')
print('value')
Correct.
R
h1 {{ font-size:31px color:red; }}
h1 {{ font-size:31px; color:red; }}
Add semicolon.
CSS
if b = 66:
if b == 66:
Use == for comparison.
Python
for (int i=0; i<17; i++) {{}}
for (int i=0; i<17; i++) {{}}
Correct.
Java
for (val in list)
for (val of list)
for...in iterates keys.
JavaScript
if (bar = 68)
if (bar == 68)
Use ==.
Scala
if (val = 87) {{}}
if (val == 87) {{}}
Use ==.
Java
if c = 90 {{}}
if c == 90 {{}}
Use ==.
Swift
items[9]
if (length(items) >= 9) items[9]
Check length.
R
echo 'message'
echo 'message';
Add semicolon.
PHP
var b int = 'result'
var b string = 'result'
Type mismatch.
Go
if data > 78 print('info')
if data > 78: print('info')
Colon missing after if.
Python
<?php // code ?>
<?php // code ?>
Correct.
PHP
if (a) console.log('yes') else console.log('no')
if (a) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
$temp = 18; if ($temp = 18) {{}}
$temp = 18; if ($temp == 18) {{}}
Use ==.
PHP
let data = 61; data += 1;
let mut data = 61; data += 1;
Need mut to modify.
Rust
void main() {{ print('value') }}
void main() {{ print('value'); }}
Add semicolon.
Dart
my @arr = (66,39,5);
my @arr = (66,39,5);
Correct.
Perl
var x = 46;
var x = 46;
Correct.
Dart
<person><desc>output</desc><age>93</age></person
<person><desc>output</desc><age>93</age></person>
Add closing >.
XML
for i=1,36 do print(i) end
for i=1,36 do print(i) end
Correct.
Lua
list[90]
if (list.indices.contains(90)) list[90]
Check index.
Kotlin
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
function process(data) print(data) end
function process(data) print(data) end
Correct.
Lua
var x int
var x int
Correct.
Go
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
cin >> b cout << b;
cin >> b; cout << b;
Add semicolon.
C++
let val: i32 = "info";
let val: &str = "info";
Type mismatch.
Rust
<note name='data'/>
<note name="data"/>
Double quotes.
XML
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
<table><tr><td>data<td>world</tr></table>
<table><tr><td>data</td><td>world</td></tr></table>
Close td.
HTML
[19, 25, 45
[19, 25, 45]
Close bracket.
Python
println('data')
println("data")
Double quotes.
Scala
$items[36]
if ($items.Count -gt 36) {{ $items[36] }}
Check bounds.
PowerShell
<person age=69>
<person age="69">
Quote attribute.
XML
if ($x = 22)
if ($x == 22)
Use ==.
Perl
while read line; do echo $line; done < data.txt
while read line; do echo $line; done < data.txt
Correct.
Shell
def foo(y): return y + 1
def foo(y): return y + 1
Correct.
Python
UPDATE users SET status='result' WHERE email=54
UPDATE users SET status='result' WHERE email=54;
Add semicolon.
SQL
let val: number | null = null; val.toFixed(62);
let val: number | null = null; if(val!==null) val.toFixed(62);
Null check.
TypeScript
if foo = 22
if foo == 22
Use ==.
Go
yield foo
yield foo
Correct yield.
Python
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
class = 'output'
class_name = 'output'
'class' is a keyword.
Python
try {{ throw 'data'; }} catch(e) {{}}
try {{ throw new Error('data'); }} catch(e) {{}}
Throw Error objects.
JavaScript
with open('data.txt') as fp: data = fp.read()
with open('data.txt') as fp: data = fp.read()
Correct.
Python
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
<center>result</center>
<div style='text-align:center;'>result</div>
Use CSS.
HTML
disp('hello')
disp('hello')
Correct.
MATLAB
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
fmt.Println 'test'
fmt.Println('test')
Missing parentheses.
Go
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
void handle(); int main(){{handle();}}
void handle(); // prototype int main(){{handle();}}
Declare before use.
C++
int items[36]; items[36]=5;
int items[36]; if(36<36){{}} else items[36]=5;
Bounds check.
C++
local a = 69
local a = 69
Correct.
Lua
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
'data' + 29
'data' + str(29)
Can't add int to string.
Python
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
#main {{ color: red; }}
#main {{ color: red; }}
Correct.
CSS
<p>test <b>hello</p></b>
<p>test <b>hello</b></p>
Nest properly.
HTML
JOIN products ON users.id = products.age
JOIN products ON users.id = products.age
Correct.
SQL
fs.readFile('input.csv', (err,data) => {{ if(err) throw err; }});
fs.readFile('input.csv', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
if (count = 25) {}
if (count == 25) {}
Use ==.
Dart
switch(item){{ case 90: break; }}
switch(item){{ case 90: break; default: break; }}
Add default case.
Java
if ($bar = 37) {{}}
if ($bar -eq 37) {{}}
Use -eq.
PowerShell
age: world status: hello,
age: world status: hello
Remove comma.
YAML
{ "name": "message" }
{ "name": "message" }
Correct.
JSON
const http = require('http'); http.createServer((req,res) => res.end('value')).listen(37);
const http = require('http'); http.createServer((req,res) => res.end('value')).listen(37);
Correct.
Node.js
json.sqrt(64)
import json json.sqrt(64)
Import module first.
Python
let c: number = 'result';
let c: string = 'result';
Fix type.
TypeScript
if (y = 51)
if (y == 51)
Use ==.
C++
echo data world
echo 'data world'
Quote to prevent splitting.
Shell
let text1 = String::from("test"); let str2 = text1; println!("{{}}", text1);
let text1 = String::from("test"); let str2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust