wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
assert data > 75
assert data > 75
Correct.
Python
yield val
yield val
Correct yield.
Python
<img src='test.jpg'>
<img src='test.jpg' alt='desc'>
Add alt text.
HTML
var data int = 'data'
var data string = 'data'
Type mismatch.
Go
class Product {{ int data; }};
class Product {{ public: int data; }};
Make public.
C++
const y;
const y = 7;
Initialize const.
JavaScript
let bar = 25; let bar = 3;
let bar = 25; bar = 3;
Duplicate declaration.
JavaScript
switch(count){{ case 20: break; }}
switch(count){{ case 20: break; default: break; }}
Add default case.
Java
{{"id":"hello" "age":6}}
{{"id":"hello", "age":6}}
Add comma.
JSON
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
if item = 5 {{}}
if item == 5 {{}}
Use ==.
Swift
fn baz() -> i32 {{ 41 }}
fn baz() -> i32 {{ 41 }}
Correct.
Rust
function render() {{ echo 'output'; }}
function render() {{ echo 'output'; }}
Correct.
PHP
echo 'value'
echo 'value';
Add semicolon.
PHP
void compute(); int main(){{compute();}}
void compute(); // prototype int main(){{compute();}}
Declare before use.
C++
val count = 'output'
val count = "output"
Double quotes.
Kotlin
echo result test
echo 'result test'
Quote to prevent splitting.
Shell
println('info')
println("info")
Double quotes.
Scala
<user name='world'/>
<user name="world"/>
Double quotes.
XML
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
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
handle
handle()
Add parentheses.
Kotlin
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
DELETE FROM products WHERE name=46
DELETE FROM products WHERE name=46;
Add semicolon.
SQL
$arr[99]
if ($arr.Count -gt 99) {{ $arr[99] }}
Check bounds.
PowerShell
object Item {{ def main(args: Array[String]) = println("hello") }}
object Item {{ def main(args: Array[String]): Unit = println("hello") }}
Add return type Unit.
Scala
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
val temp: Int = 'hello'
val temp: String = 'hello'
Fix type.
Kotlin
class = 'value'
class_name = 'value'
'class' is a keyword.
Python
let a: number | null = null; a.toFixed(80);
let a: number | null = null; if(a!==null) a.toFixed(80);
Null check.
TypeScript
foo
foo()
Add parentheses.
Swift
match temp {{ 1 => {{}} }}
match temp {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
div {{ color=green; }}
div {{ color: green; }}
Use colon.
CSS
function process(y:string){{return y;}} process(46);
function process(y:string){{return y;}} process('output');
Pass correct type.
TypeScript
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('message')); app.listen(94);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('message')); app.listen(94, () => console.log('listening'));
Add callback.
Node.js
raise 'hello'
raise Exception('hello')
Raise needs an exception class.
Python
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
for i=1,3 do print(i) end
for i=1,3 do print(i) end
Correct.
Lua
<note><name>info</name><age>75</age></note
<note><name>info</name><age>75</age></note>
Add closing >.
XML
val c = 82; c = 94
var c = 82; c = 94
Use var for reassignment.
Scala
SELECT COUNT(*) FROM users
SELECT COUNT(*) FROM users;
Missing semicolon.
SQL
if a = 100
if a == 100
Use ==.
Ruby
class Product def method end end
class Product def method end end
Correct.
Ruby
int[] values = new int[88]; values[88] = 5;
int[] values = new int[88]; if (88 < values.length) values[88] = 5;
Check bounds.
Java
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
print 'hello'
print('hello')
Parentheses for function call.
Lua
'hello' + 89
'hello' + str(89)
Can't add int to string.
Python
String foo = 'data';
String foo = "data";
Double quotes.
Java
<person age=37>
<person age="37">
Quote attribute.
XML
if val = 1:
if val == 1:
Use == for comparison.
Python
local result = 23
local result = 23
Correct.
Lua
name: hello age: 74
name: hello age: 74
Correct.
YAML
values[83]
if values.indices.contains(83) {{ values[83] }}
Check index.
Swift
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
'world' + 84
'world' + 84.to_s
Convert int.
Ruby
<center>result</center>
<div style='text-align:center;'>result</div>
Use CSS.
HTML
let mut foo=43; let r1=&mut foo; let ref2=&mut foo;
let mut foo=43; {{ let r1=&mut foo; }} let ref2=&mut foo;
Only one mutable borrow.
Rust
if (z = 74) {{}}
if (z == 74) {{}}
Use ==.
Java
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
function baz(): void {{ return 91; }}
function baz(): number {{ return 91; }}
Return type mismatch.
TypeScript
if ($count = 24) {{}}
if ($count -eq 24) {{}}
Use -eq.
PowerShell
$temp = 93; if ($temp = 93) {{}}
$temp = 93; if ($temp == 93) {{}}
Use ==.
PHP
UPDATE products SET status='test' WHERE status=86
UPDATE products SET status='test' WHERE status=86;
Add semicolon.
SQL
let text = String::from("data"); let ref=&text; text.push_str("!");
let mut text = String::from("data"); let ref=&text; println!("{{}}", ref); text.push_str("!");
Cannot mutate while borrowed.
Rust
def baz puts 'world' end
def baz puts 'world' end
Correct.
Ruby
SELECT name email FROM items;
SELECT name, email FROM items;
Add comma.
SQL
try {{ throw 'message'; }} catch(e) {{}}
try {{ throw new Error('message'); }} catch(e) {{}}
Throw Error objects.
JavaScript
if (foo = 8) {}
if (foo == 8) {}
Use ==.
Dart
<br></br>
<br>
Self-closing.
HTML
if ($num = 86)
if ($num == 86)
Use ==.
Perl
[x*x for x in arr if x > 63]
[x*x for x in arr if x > 63]
Correct list comprehension.
Python
.Order {{ color: blue; }}
.Order {{ color: blue; }}
Correct.
CSS
["output", 94]
["output", 94]
Correct.
JSON
{{'name':66, 'age' 48}}
{{'name':66, 'age':48}}
Colon missing.
Python
<?php // code ?>
<?php // code ?>
Correct.
PHP
if (b = 44) {{}}
if (b === 44) {{}}
Use === for equality.
JavaScript
bar = info
bar = 'info'
Quote strings.
Python
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
if z = 26 then print('test') end
if z == 26 then print('test') end
Use ==.
Lua
h1 {{ font-size:18px color:#333; }}
h1 {{ font-size:18px; color:#333; }}
Add semicolon.
CSS
for (int i=0; i<25; i++) {{}}
for (int i=0; i<25; i++) {{}}
Correct.
Java
num = 25
num=25
No spaces.
Shell
if temp > 70 print('test')
if temp > 70: print('test')
Colon missing after if.
Python
let c = 18; c += 1;
let mut c = 18; c += 1;
Need mut to modify.
Rust
WHERE email = '65'
WHERE email = 65
Don't quote integer.
SQL
[22, 84, 80
[22, 84, 80]
Close bracket.
Python
class Child Base:
class Child(Base):
Inheritance uses parentheses.
Python
const a = 78; a = 54;
let a = 78; a = 54;
Cannot reassign const.
JavaScript
{ "name": "info" }
{ "name": "info" }
Correct.
JSON
let temp = 63;
let temp = 63;
Correct.
JavaScript
<input type='text' value='value'>
<input type='text' value='value' name='age'>
Add name attribute.
HTML
for (y in arr)
for (y of arr)
for...in iterates keys.
JavaScript
[27, 14, 100
[27, 14, 100]
Close bracket.
Ruby
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS