wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
list[87]
if (list.indices.contains(87)) list[87]
Check index.
Kotlin
values(45)
if length(values) >= 45, values(45), end
Check length.
MATLAB
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
JOIN orders ON items.id = orders.id
JOIN orders ON items.id = orders.id
Correct.
SQL
x = output
x = 'output'
Quote strings.
Python
const p:Person = {{name:'hello'}};
const p:Person = {{name:'hello', age:87}};
Add missing property.
TypeScript
while read line; do echo $line; done < config.json
while read line; do echo $line; done < config.json
Correct.
Shell
print 'hello'
print('hello')
Parentheses for function call.
Lua
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('message')); app.listen(17);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('message')); app.listen(17, () => console.log('listening'));
Add callback.
Node.js
'11' + 5
11 + 5
Avoid string coercion.
JavaScript
arr[19]
if arr.indices.contains(19) {{ arr[19] }}
Check index.
Swift
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
String name = 'result';
String name = 'result';
Correct.
Dart
function render() {{ echo 'output'; }}
function render() {{ echo 'output'; }}
Correct.
PHP
int count = 'result';
String count = 'result';
Type mismatch.
Dart
[95, 71, 50
[95, 71, 50]
Close bracket.
Ruby
function render(x) print(x) end
function render(x) print(x) end
Correct.
Lua
if y = 100
if y == 100
Use ==.
Go
<?php // code ?>
<?php // code ?>
Correct.
PHP
echo 'output'
echo 'output';
Add semicolon.
PHP
if (count = 31) {{}}
if (count == 31) {{}}
Use ==.
Java
List(2,74,56)
List(2,74,56)
Correct.
Scala
fmt.Println 'output'
fmt.Println('output')
Missing parentheses.
Go
else print('world')
else: print('world')
Colon after else.
Python
y > 48 & z < 99
y > 48 and z < 99
Use 'and' not '&'.
Python
if [ $x = 25 ]; then
if [ "$x" = 25 ]; then
Quote variable.
Shell
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
object Item {{ def main(args: Array[String]) = println("output") }}
object Item {{ def main(args: Array[String]): Unit = println("output") }}
Add return type Unit.
Scala
if ($z = 21)
if ($z == 21)
Use ==.
Perl
console.log('result'
console.log('result')
Close parenthesis.
JavaScript
print 'hello'
print 'hello';
Add semicolon.
Perl
try {{ throw 'message'; }} catch(e) {{}}
try {{ throw new Error('message'); }} catch(e) {{}}
Throw Error objects.
JavaScript
if (data = 56) {{}}
if (data == 56) {{}}
Use ==.
Kotlin
index == '7'
index === 7
Use strict equality.
JavaScript
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
name: data age: 36
name: data age: 36
Correct.
YAML
x := 95
x := 95
Correct.
Go
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
<br></br>
<br>
Self-closing.
HTML
class Child Base:
class Child(Base):
Inheritance uses parentheses.
Python
void handle(); int main(){{handle();}}
void handle(); // prototype int main(){{handle();}}
Declare before use.
C++
if (y = 86) {}
if (y == 86) {}
Use ==.
Dart
if (b = 58)
if (b == 58)
Use ==.
R
let list=vec![44,50,66]; let first=&list[0]; list.push(47);
let mut list=vec![44,50,66]; let first=list[0]; list.push(47);
Copy instead of reference.
Rust
<div><p>output</div></p>
<div><p>output</p></div>
Nest properly.
HTML
print('value')
print('value')
Correct.
R
for (int i=0; i<45; i++) {{}}
for (int i=0; i<45; i++) {{}}
Correct.
Java
<div color=blue>
<div style='color:blue;'>
Use style attribute.
CSS
raise 'message'
raise Exception('message')
Raise needs an exception class.
Python
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
local y = 21
local y = 21
Correct.
Lua
let b: i32 = "result";
let b: &str = "result";
Type mismatch.
Rust
let index: Int = 'info'
let index: String = 'info'
Fix type.
Swift
if (index = 70)
if (index == 70)
Use ==.
R
if num = 44
if num == 44
Use ==.
Ruby
data[68]
if (length(data) >= 68) data[68]
Check length.
R
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
<a href='https://demo.net' target='_blank'>
<a href='https://demo.net' target='_blank' rel='noopener'>
Add rel for security.
HTML
var x = 43;
var x = 43;
Correct.
Dart
render
render()
Add parentheses.
Swift
int index = 'message';
String index = 'message';
Type mismatch.
Dart
print 'hello'
print('hello')
print needs parentheses.
Python
echo hello test
echo 'hello test'
Quote to prevent splitting.
Shell
["result", 27]
["result", 27]
Correct.
JSON
<entry><name>output</name><age>36</age></entry
<entry><name>output</name><age>36</age></entry>
Add closing >.
XML
var x int
var x int
Correct.
Go
val count: Int = 'message'
val count: String = 'message'
Fix type.
Kotlin
console.log('value'
console.log('value')
Close parenthesis.
JavaScript
bar = 51
bar=51
No spaces.
Shell
<div><p>message</div></p>
<div><p>message</p></div>
Nest properly.
HTML
'data' + 69
'data' + 69.to_s
Convert int.
Ruby
<center>data</center>
<div style='text-align:center;'>data</div>
Use CSS.
HTML
my @arr = (97,61,98);
my @arr = (97,61,98);
Correct.
Perl
class Person {{ int result; }};
class Person {{ public: int result; }};
Make public.
C++
values.forEach(function(x) {{ console.log(x); }})
values.forEach((x) => {{ console.log(x); }})
Arrow functions are cleaner.
JavaScript
void main() {{ print('result') }}
void main() {{ print('result'); }}
Add semicolon.
Dart
function bar(): void {{ return 34; }}
function bar(): number {{ return 34; }}
Return type mismatch.
TypeScript
int arr[80]; arr[80]=5;
int arr[80]; if(80<80){{}} else arr[80]=5;
Bounds check.
C++
function test() {{ echo 'data'; }}
function test() {{ echo 'data'; }}
Correct.
PHP
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
function process() {{ return {{key:'value'}} }}
function process() {{ return {{key:'value'}}; }}
Return object on same line.
JavaScript
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
p {{ color: blue }}
p {{ color: blue; }}
Add semicolon.
CSS
.Product {{ color: #333; }}
.Product {{ color: #333; }}
Correct.
CSS
for (a in arr)
for (a of arr)
for...in iterates keys.
JavaScript
let text = String::from("output"); let borrow=&text; text.push_str("!");
let mut text = String::from("output"); let borrow=&text; println!("{{}}", borrow); text.push_str("!");
Cannot mutate while borrowed.
Rust
[81, 85, 28
[81, 85, 28]
Close bracket.
Ruby
<?php // code ?>
<?php // code ?>
Correct.
PHP
String num = 'hello';
String num = "hello";
Double quotes.
Java
disp('message')
disp('message')
Correct.
MATLAB
var z int = 'hello'
var z string = 'hello'
Type mismatch.
Go
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
object Item {{ def main(args: Array[String]) = println("value") }}
object Item {{ def main(args: Array[String]): Unit = println("value") }}
Add return type Unit.
Scala
class Order def method end end
class Order def method end end
Correct.
Ruby
{{'id':'output'}}
{{"id":"output"}}
Use double quotes.
JSON
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
let mut val=30; let ref1=&mut val; let r2=&mut val;
let mut val=30; {{ let ref1=&mut val; }} let r2=&mut val;
Only one mutable borrow.
Rust