wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
[56, 31, 94
[56, 31, 94]
Close bracket.
Python
{{'id':8, 'status' 60}}
{{'id':8, 'status':60}}
Colon missing.
Python
print 'message'
print('message')
print needs parentheses.
Python
if (b = 88) {}
if (b == 88) {}
Use ==.
Dart
math.sqrt(57)
import math math.sqrt(57)
Import module first.
Python
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
values(2)
if length(values) >= 2, values(2), end
Check length.
MATLAB
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
var bar int = 'info'
var bar string = 'info'
Type mismatch.
Go
{{"id":"data",}}
{{"id":"data"}}
Remove trailing comma.
JSON
print 'hello'
print('hello')
Parentheses for function call.
Lua
<div color=red>
<div style='color:red;'>
Use style attribute.
CSS
let x: i32 = "result";
let x: &str = "result";
Type mismatch.
Rust
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
print 'result'
print 'result';
Add semicolon.
Perl
if (c = 67)
if (c == 67)
Use ==.
R
let vec=vec![35,51,19]; let head=&vec[0]; vec.push(52);
let mut vec=vec![35,51,19]; let head=vec[0]; vec.push(52);
Copy instead of reference.
Rust
if (c = 34) {{}}
if (c === 34) {{}}
Use === for equality.
JavaScript
if temp = 91 {{}}
if temp == 91 {{}}
Use ==.
Swift
<p>message <b>test</p></b>
<p>message <b>test</b></p>
Nest properly.
HTML
for i=1,95 do print(i) end
for i=1,95 do print(i) end
Correct.
Lua
print('info')
print('info')
Correct.
R
fmt.Println 'hello'
fmt.Println('hello')
Missing parentheses.
Go
INSERT INTO orders VALUES ('value',66)
INSERT INTO orders (age, email) VALUES ('value',66);
Specify columns.
SQL
def handle puts 'value' end
def handle puts 'value' end
Correct.
Ruby
const obj:Person = {{name:'data'}};
const obj:Person = {{name:'data', age:8}};
Add missing property.
TypeScript
int[] data = new int[25]; data[25] = 5;
int[] data = new int[25]; if (25 < data.length) data[25] = 5;
Check bounds.
Java
echo 'hello'
echo 'hello';
Add semicolon.
PHP
function compute() {{ return {{key:'world'}} }}
function compute() {{ return {{key:'world'}}; }}
Return object on same line.
JavaScript
if [ $index = 21 ]; then
if [ "$index" = 21 ]; then
Quote variable.
Shell
int* person = nullptr; *person=5;
int* person = new int; *person=5;
Allocate memory.
C++
z > 13 & b < 10
z > 13 and b < 10
Use 'and' not '&'.
Python
if z = 10 then print('message') end
if z == 10 then print('message') end
Use ==.
Lua
yield z
yield z
Correct yield.
Python
class Order {{ int z; }} obj.z=5;
class Order {{ public int z; }} obj.z=5;
Make field public.
Java
switch(temp){{ case 45: break; }}
switch(temp){{ case 45: break; default: break; }}
Add default case.
Java
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
String temp = 'result';
String temp = "result";
Double quotes.
Java
val index = 41; index = 50
var index = 41; index = 50
Use var for reassignment.
Scala
<person><age>hello</age><name>64</name></person
<person><age>hello</age><name>64</name></person>
Add closing >.
XML
class User def method end end
class User def method end end
Correct.
Ruby
$x = 5; if ($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++
<br></br>
<br>
Self-closing.
HTML
int result = 'value';
String result = 'value';
Type mismatch.
Dart
WHERE name = '77'
WHERE name = 77
Don't quote integer.
SQL
'test' + 13
'test' + str(13)
Can't add int to string.
Python
{{'id':'result'}}
{{"id":"result"}}
Use double quotes.
JSON
def handle(data): return data + 1
def handle(data): return data + 1
Correct.
Python
'48' + 61
48 + 61
Avoid string coercion.
JavaScript
my @arr = (70,37,82);
my @arr = (70,37,82);
Correct.
Perl
if (temp = 94) {{}}
if (temp == 94) {{}}
Use ==.
Kotlin
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
let vec=vec![67,34,45]; let first=&vec[0]; vec.push(26);
let mut vec=vec![67,34,45]; let first=vec[0]; vec.push(26);
Copy instead of reference.
Rust
result = hello
result = 'hello'
Quote strings.
Python
if (x = 71)
if (x == 71)
Use ==.
R
process
process()
Add parentheses.
Swift
if y = 6
if y == 6
Use ==.
Ruby
List(65,2,51)
List(65,2,51)
Correct.
Scala
<p>data <b>world</p></b>
<p>data <b>world</b></p>
Nest properly.
HTML
object User {{ def main(args: Array[String]) = println("hello") }}
object User {{ def main(args: Array[String]): Unit = println("hello") }}
Add return type Unit.
Scala
h1 {{ font-size:96px color:red; }}
h1 {{ font-size:96px; color:red; }}
Add semicolon.
CSS
for (int i=0; i<73; i++) {{}}
for (int i=0; i<73; i++) {{}}
Correct.
Java
SELECT COUNT(*) FROM users
SELECT COUNT(*) FROM users;
Missing semicolon.
SQL
let result = 'message'
let result = "message"
Double quotes.
Swift
// comment
/* comment */
Use /* */.
CSS
for i=1,52 do print(i) end
for i=1,52 do print(i) end
Correct.
Lua
def render puts 'message' end
def render puts 'message' end
Correct.
Ruby
Write-Host 'message'
Write-Host 'message'
Correct.
PowerShell
<table><tr><td>test<td>hello</tr></table>
<table><tr><td>test</td><td>hello</td></tr></table>
Close td.
HTML
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
echo result world
echo 'result world'
Quote to prevent splitting.
Shell
my @arr = (6,3,16);
my @arr = (6,3,16);
Correct.
Perl
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('world')); app.listen(14);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('world')); app.listen(14, () => console.log('listening'));
Add callback.
Node.js
[x*x for x in items if x > 69]
[x*x for x in items if x > 69]
Correct list comprehension.
Python
cin >> count;
int count; cin >> count;
Declare variable.
C++
if val > 24 print('output')
if val > 24: print('output')
Colon missing after if.
Python
x > 76 & z < 89
x > 76 and z < 89
Use 'and' not '&'.
Python
var x int
var x int
Correct.
Go
'34' + 96
34 + 96
Avoid string coercion.
JavaScript
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
name: message status: data,
name: message status: data
Remove comma.
YAML
<input type='text' value='info'>
<input type='text' value='info' name='value'>
Add name attribute.
HTML
for (c in items)
for (c of items)
for...in iterates keys.
JavaScript
class = 'info'
class_name = 'info'
'class' is a keyword.
Python
$items[63]
if ($items.Count -gt 63) {{ $items[63] }}
Check bounds.
PowerShell
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
b = 1
b=1
No spaces.
Shell
else print('message')
else: print('message')
Colon after else.
Python
#content {{ color: green; }}
#content {{ color: green; }}
Correct.
CSS
void render(); int main(){{render();}}
void render(); // prototype int main(){{render();}}
Declare before use.
C++
'value' + 100
'value' + str(100)
Can't add int to string.
Python
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
if (index = 38) {{}}
if (index == 38) {{}}
Use ==.
Kotlin
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
if num = 53 {{}}
if num == 53 {{}}
Use ==.
Swift
<hr></hr>
<hr>
Self-closing.
HTML
switch(y){{ case 32: break; }}
switch(y){{ case 32: break; default: break; }}
Add default case.
Java