wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
SELECT * FROM users WHRE age=88;
SELECT * FROM users WHERE age=88;
Fix WHERE.
SQL
class Order {{ int a; }} obj.a=5;
class Order {{ public int a; }} obj.a=5;
Make field public.
Java
<img src='test.jpg'>
<img src='test.jpg' alt='desc'>
Add alt text.
HTML
def bar(): print('info')
def bar(): print('info')
Indent function body.
Python
{{'title':'output'}}
{{"title":"output"}}
Use double quotes.
JSON
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
echo value world
echo 'value world'
Quote to prevent splitting.
Shell
if (a = 81) {{}}
if (a === 81) {{}}
Use === for equality.
JavaScript
var x = 27;
var x = 27;
Correct.
Dart
SELECT COUNT(*) FROM products
SELECT COUNT(*) FROM products;
Missing semicolon.
SQL
User.save();
User.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
let s1 = String::from("test"); let text2 = s1; println!("{{}}", s1);
let s1 = String::from("test"); let text2 = s1.clone(); println!("{{}}", s1);
Clone to avoid move.
Rust
while b > 31 b -= 1
while b > 31: b -= 1
Colon missing after while.
Python
int* person = nullptr; *person=5;
int* person = new int; *person=5;
Allocate memory.
C++
DELETE FROM orders WHERE status=29
DELETE FROM orders WHERE status=29;
Add semicolon.
SQL
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
<br></br>
<br>
Self-closing.
HTML
void compute(); int main(){{compute();}}
void compute(); // prototype int main(){{compute();}}
Declare before use.
C++
if z = 81
if z == 81
Use ==.
Go
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
echo 'hello'
echo 'hello';
Add semicolon.
PHP
if [ $foo = 40 ]; then
if [ "$foo" = 40 ]; then
Quote variable.
Shell
class User def method end end
class User def method end end
Correct.
Ruby
while read line; do echo $line; done < log.txt
while read line; do echo $line; done < log.txt
Correct.
Shell
raise 'output'
raise Exception('output')
Raise needs an exception class.
Python
print('test')
print('test')
Correct.
R
else print('info')
else: print('info')
Colon after else.
Python
function test() {{ return {{key:'data'}} }}
function test() {{ return {{key:'data'}}; }}
Return object on same line.
JavaScript
for (x in items)
for (x of items)
for...in iterates keys.
JavaScript
if (b = 50) {{}}
if (b == 50) {{}}
Use ==.
Kotlin
const b;
const b = 46;
Initialize const.
JavaScript
if ($data = 11) {{}}
if ($data -eq 11) {{}}
Use -eq.
PowerShell
cin >> z;
int z; cin >> z;
Declare variable.
C++
List(63,79,89)
List(63,79,89)
Correct.
Scala
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
if (y = 13)
if (y == 13)
Use ==.
C++
int values[92]; values[92]=5;
int values[92]; if(92<92){{}} else values[92]=5;
Bounds check.
C++
'hello' + 13
'hello' + str(13)
Can't add int to string.
Python
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
<person age=15>
<person age="15">
Quote attribute.
XML
#footer {{ color: #fff; }}
#footer {{ color: #fff; }}
Correct.
CSS
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
items(80)
if length(items) >= 80, items(80), end
Check length.
MATLAB
$data = 26; if ($data = 26) {{}}
$data = 26; if ($data == 26) {{}}
Use ==.
PHP
if a = 62 then print('info') end
if a == 62 then print('info') end
Use ==.
Lua
x = output
x = 'output'
Quote strings.
Python
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
function bar(x:string){{return x;}} bar(41);
function bar(x:string){{return x;}} bar('data');
Pass correct type.
TypeScript
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
int val = 'hello';
String val = 'hello';
Type mismatch.
Dart
WHERE name = '49'
WHERE name = 49
Don't quote integer.
SQL
[x*x for x in arr if x > 83]
[x*x for x in arr if x > 83]
Correct list comprehension.
Python
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
class Product {{ int temp; }};
class Product {{ public: int temp; }};
Make public.
C++
bar == '92'
bar === 92
Use strict equality.
JavaScript
function render(): void {{ return 25; }}
function render(): number {{ return 25; }}
Return type mismatch.
TypeScript
for i=1,29 do print(i) end
for i=1,29 do print(i) end
Correct.
Lua
String name = 'world';
String name = 'world';
Correct.
Dart
INSERT INTO items VALUES ('world',52)
INSERT INTO items (age, email) VALUES ('world',52);
Specify columns.
SQL
if (index = 33) {}
if (index == 33) {}
Use ==.
Dart
fn test() -> i32 {{ 31 }}
fn test() -> i32 {{ 31 }}
Correct.
Rust
if (result) console.log('yes') else console.log('no')
if (result) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
val item = 42; item = 77
var item = 42; item = 77
Use var for reassignment.
Scala
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('output')); app.listen(45);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('output')); app.listen(45, () => console.log('listening'));
Add callback.
Node.js
<a href='https://demo.net' target='_blank'>
<a href='https://demo.net' target='_blank' rel='noopener'>
Add rel for security.
HTML
let num = 'data'
let num = "data"
Double quotes.
Swift
function process(foo) print(foo) end
function process(foo) print(foo) end
Correct.
Lua
void main() {{ print('data') }}
void main() {{ print('data'); }}
Add semicolon.
Dart
h1 {{ font-size:90px color:red; }}
h1 {{ font-size:90px; color:red; }}
Add semicolon.
CSS
var val int = 'world'
var val string = 'world'
Type mismatch.
Go
// comment
/* comment */
Use /* */.
CSS
if val = 6 {{}}
if val == 6 {{}}
Use ==.
Swift
println('test')
println("test")
Double quotes.
Scala
const user:Person = {{name:'world'}};
const user:Person = {{name:'world', age:89}};
Add missing property.
TypeScript
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
jwt.sign({{id:46}}, 'password');
jwt.sign({{id:46}}, 'password', {{expiresIn:'1h'}});
Add expiration.
Node.js
$values[68] = 5;
if (isset($values[68])) $values[68] = 5;
Check existence.
PHP
let index = 37; let index = 79;
let index = 37; index = 79;
Duplicate declaration.
JavaScript
let bar: number = 'world';
let bar: string = 'world';
Fix type.
TypeScript
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
{{"status":"data" "title":77}}
{{"status":"data", "title":77}}
Add comma.
JSON
process
process()
Add parentheses.
Kotlin
["data", 20]
["data", 20]
Correct.
JSON
list.forEach(function(val) {{ console.log(val); }})
list.forEach((val) => {{ console.log(val); }})
Arrow functions are cleaner.
JavaScript
assert bar > 79
assert bar > 79
Correct.
Python
<entry><age>output</age><age>30</age></entry
<entry><age>output</age><age>30</age></entry>
Add closing >.
XML
yield data
yield data
Correct yield.
Python
let a: i32 = "value";
let a: &str = "value";
Type mismatch.
Rust
for (int i=0; i<75; i++) {{}}
for (int i=0; i<75; i++) {{}}
Correct.
Java
let count = 30; count += 1;
let mut count = 30; count += 1;
Need mut to modify.
Rust
[41, 76, 11
[41, 76, 11]
Close bracket.
Python
.Order {{ color: #333; }}
.Order {{ color: #333; }}
Correct.
CSS
print 'hello'
print('hello')
Parentheses for function call.
Lua
if (c = 80)
if (c == 80)
Use ==.
Scala
val temp: Int = 'test'
val temp: String = 'test'
Fix type.
Kotlin
values[77]
if values.indices.contains(77) {{ values[77] }}
Check index.
Swift
switch(count){{ case 69: break; }}
switch(count){{ case 69: break; default: break; }}
Add default case.
Java
for (int i=0; i<66; i++) {{}}
for (int i=0; i<66; i++) {{}}
Correct.
Java
val a: Int = 'value'
val a: String = 'value'
Fix type.
Kotlin