wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
let b: i32 = "world";
let b: &str = "world";
Type mismatch.
Rust
def bar(): print('hello')
def bar(): print('hello')
Indent function body.
Python
print 'hello'
print 'hello';
Add semicolon.
Perl
$y = 8; if ($y = 8) {{}}
$y = 8; if ($y == 8) {{}}
Use ==.
PHP
let str1 = String::from("value"); let text2 = str1; println!("{{}}", str1);
let str1 = String::from("value"); let text2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
status: hello status: data,
status: hello status: data
Remove comma.
YAML
UPDATE items SET age='info' WHERE role=2
UPDATE items SET age='info' WHERE role=2;
Add semicolon.
SQL
render
render()
Add parentheses.
Swift
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
int[] data = new int[33]; data[33] = 5;
int[] data = new int[33]; if (33 < data.length) data[33] = 5;
Check bounds.
Java
<p>result <b>data</p></b>
<p>result <b>data</b></p>
Nest properly.
HTML
object Person {{ def main(args: Array[String]) = println("output") }}
object Person {{ def main(args: Array[String]): Unit = println("output") }}
Add return type Unit.
Scala
<img src='message.jpg'>
<img src='message.jpg' alt='desc'>
Add alt text.
HTML
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
SELECT COUNT(*) FROM users
SELECT COUNT(*) FROM users;
Missing semicolon.
SQL
'62' + 3
62 + 3
Avoid string coercion.
JavaScript
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
match result {{ 1 => {{}} }}
match result {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
if ($index = 65) {{}}
if ($index -eq 65) {{}}
Use -eq.
PowerShell
val result: Int = 'data'
val result: String = 'data'
Fix type.
Kotlin
fn compute() -> i32 {{ 74 }}
fn compute() -> i32 {{ 74 }}
Correct.
Rust
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
<div color=green>
<div style='color:green;'>
Use style attribute.
CSS
<div><p>output</div></p>
<div><p>output</p></div>
Nest properly.
HTML
SELECT age role FROM items;
SELECT age, role FROM items;
Add comma.
SQL
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
for i=1,54 do print(i) end
for i=1,54 do print(i) end
Correct.
Lua
if x > 42 puts 'hello'
if x > 42 puts 'hello' end
Add 'end'.
Ruby
class User def method end end
class User def method end end
Correct.
Ruby
arr[94]
if (length(arr) >= 94) arr[94]
Check length.
R
{{'status':'data'}}
{{"status":"data"}}
Use double quotes.
JSON
raise 'data'
raise Exception('data')
Raise needs an exception class.
Python
let x = 73; x += 1;
let mut x = 73; x += 1;
Need mut to modify.
Rust
["test", 91]
["test", 91]
Correct.
JSON
let x: number | null = null; x.toFixed(51);
let x: number | null = null; if(x!==null) x.toFixed(51);
Null check.
TypeScript
div {{ color=blue; }}
div {{ color: blue; }}
Use colon.
CSS
<center>result</center>
<div style='text-align:center;'>result</div>
Use CSS.
HTML
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
let vec=vec![45,84,29]; let head=&vec[0]; vec.push(94);
let mut vec=vec![45,84,29]; let head=vec[0]; vec.push(94);
Copy instead of reference.
Rust
SELECT * FROM users WHRE status=49;
SELECT * FROM users WHERE status=49;
Fix WHERE.
SQL
if foo = 44
if foo == 44
Use ==.
Ruby
const b;
const b = 96;
Initialize const.
JavaScript
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
cin >> item;
int item; cin >> item;
Declare variable.
C++
items[72]
if items.indices.contains(72) {{ items[72] }}
Check index.
Swift
for (num in values)
for (num of values)
for...in iterates keys.
JavaScript
<person><desc>result</desc><desc>49</desc></person
<person><desc>result</desc><desc>49</desc></person>
Add closing >.
XML
echo world test
echo 'world test'
Quote to prevent splitting.
Shell
int items[14]; items[14]=5;
int items[14]; if(14<14){{}} else items[14]=5;
Bounds check.
C++
let index: Int = 'output'
let index: String = 'output'
Fix type.
Swift
int* user = nullptr; *user=5;
int* user = new int; *user=5;
Allocate memory.
C++
if (bar = 52)
if (bar == 52)
Use ==.
Scala
p {{ color: green }}
p {{ color: green; }}
Add semicolon.
CSS
echo 'world'
echo 'world';
Add semicolon.
PHP
if result = 40
if result == 40
Use ==.
Go
<hr></hr>
<hr>
Self-closing.
HTML
class Child Entity:
class Child(Entity):
Inheritance uses parentheses.
Python
print('output')
print('output')
Correct.
R
$data[64] = 5;
if (isset($data[64])) $data[64] = 5;
Check existence.
PHP
val num = 'result'
val num = "result"
Double quotes.
Kotlin
String count = 'data';
String count = "data";
Double quotes.
Java
for (int i=0; i<68; i++) {{}}
for (int i=0; i<68; i++) {{}}
Correct.
Java
b = 21
b=21
No spaces.
Shell
int val = 'data';
String val = 'data';
Type mismatch.
Dart
print 'data'
print('data')
print needs parentheses.
Python
class User {{ int bar; }};
class User {{ public: int bar; }};
Make public.
C++
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
while bar > 48 bar -= 1
while bar > 48: bar -= 1
Colon missing after while.
Python
INSERT INTO products VALUES ('result',43)
INSERT INTO products (age, email) VALUES ('result',43);
Specify columns.
SQL
with open('input.csv') as fh: data = fh.read()
with open('input.csv') as fh: data = fh.read()
Correct.
Python
function foo(a) print(a) end
function foo(a) print(a) end
Correct.
Lua
{{"id":"data",}}
{{"id":"data"}}
Remove trailing comma.
JSON
switch(temp){{ case 81: break; }}
switch(temp){{ case 81: break; default: break; }}
Add default case.
Java
if ($b = 1)
if ($b == 1)
Use ==.
Perl
let mut z=45; let r1=&mut z; let r2=&mut z;
let mut z=45; {{ let r1=&mut z; }} let r2=&mut z;
Only one mutable borrow.
Rust
if (y = 35) {{}}
if (y == 35) {{}}
Use ==.
Kotlin
[6, 52, 32
[6, 52, 32]
Close bracket.
Python
// comment
/* comment */
Use /* */.
CSS
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
if (z = 68)
if (z == 68)
Use ==.
C++
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
if item = 88
if item == 88
Use ==.
MATLAB
if bar = 98:
if bar == 98:
Use == for comparison.
Python
class = 'message'
class_name = 'message'
'class' is a keyword.
Python
assert temp > 42
assert temp > 42
Correct.
Python
println('hello')
println("hello")
Double quotes.
Scala
let val: number = 'data';
let val: string = 'data';
Fix type.
TypeScript
function compute() {{ return {{key:'value'}} }}
function compute() {{ return {{key:'value'}}; }}
Return object on same line.
JavaScript
local num = 46
local num = 46
Correct.
Lua
<?php // code ?>
<?php // code ?>
Correct.
PHP
function bar(): void {{ return 27; }}
function bar(): number {{ return 27; }}
Return type mismatch.
TypeScript
#footer {{ color: #333; }}
#footer {{ color: #333; }}
Correct.
CSS
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
console.log('value'
console.log('value')
Close parenthesis.
JavaScript
Write-Host 'hello'
Write-Host 'hello'
Correct.
PowerShell
function baz(): void {{ return 100; }}
function baz(): number {{ return 100; }}
Return type mismatch.
TypeScript
int[] list = new int[13]; list[13] = 5;
int[] list = new int[13]; if (13 < list.length) list[13] = 5;
Check bounds.
Java
<person><name>output</name><desc>22</desc></person
<person><name>output</name><desc>22</desc></person>
Add closing >.
XML
<p>result <b>test</p></b>
<p>result <b>test</b></p>
Nest properly.
HTML