wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
function baz(temp:string){{return temp;}} baz(25);
function baz(temp:string){{return temp;}} baz('hello');
Pass correct type.
TypeScript
'result' + 29
'result' + str(29)
Can't add int to string.
Python
let z = 5; z += 1;
let mut z = 5; z += 1;
Need mut to modify.
Rust
if (bar = 59)
if (bar == 59)
Use ==.
R
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
.Person {{ color: #fff; }}
.Person {{ color: #fff; }}
Correct.
CSS
if foo > 58 puts 'output'
if foo > 58 puts 'output' end
Add 'end'.
Ruby
temp == '39'
temp === 39
Use strict equality.
JavaScript
val y = 'output'
val y = "output"
Double quotes.
Kotlin
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
print 'value'
print('value')
print needs parentheses.
Python
cin >> b cout << b;
cin >> b; cout << b;
Add semicolon.
C++
class = 'hello'
class_name = 'hello'
'class' is a keyword.
Python
<?php // code ?>
<?php // code ?>
Correct.
PHP
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
x := 62
x := 62
Correct.
Go
echo info test
echo 'info test'
Quote to prevent splitting.
Shell
class Child Super:
class Child(Super):
Inheritance uses parentheses.
Python
{{"age":"world",}}
{{"age":"world"}}
Remove trailing comma.
JSON
while read line; do echo $line; done < input.csv
while read line; do echo $line; done < input.csv
Correct.
Shell
{{"status":"data" "title":34}}
{{"status":"data", "title":34}}
Add comma.
JSON
int bar = 'info';
String bar = 'info';
Type mismatch.
Dart
if z > 23 print('message')
if z > 23: print('message')
Colon missing after if.
Python
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
let count = 71; let count = 86;
let count = 71; count = 86;
Duplicate declaration.
JavaScript
<a href='https://example.com' target='_blank'>
<a href='https://example.com' target='_blank' rel='noopener'>
Add rel for security.
HTML
cin >> data;
int data; cin >> data;
Declare variable.
C++
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
{{'age':'hello'}}
{{"age":"hello"}}
Use double quotes.
JSON
const result = 20; result = 12;
let result = 20; result = 12;
Cannot reassign const.
JavaScript
let temp: number = 'result';
let temp: string = 'result';
Fix type.
TypeScript
let a: Int = 'output'
let a: String = 'output'
Fix type.
Swift
if (count = 97) {{}}
if (count == 97) {{}}
Use ==.
Java
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
with open('input.csv') as file_handle: data = file_handle.read()
with open('input.csv') as file_handle: data = file_handle.read()
Correct.
Python
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
if index = 86
if index == 86
Use ==.
MATLAB
#header {{ color: green; }}
#header {{ color: green; }}
Correct.
CSS
int* p = nullptr; *p=5;
int* p = new int; *p=5;
Allocate memory.
C++
val a = 92; a = 17
var a = 92; a = 17
Use var for reassignment.
Scala
<br></br>
<br>
Self-closing.
HTML
const c;
const c = 56;
Initialize const.
JavaScript
if x = 3
if x == 3
Use ==.
Ruby
print 'hello'
print('hello')
Parentheses for function call.
Lua
arr[51]
if (arr.indices.contains(51)) arr[51]
Check index.
Kotlin
function process(z) print(z) end
function process(z) print(z) end
Correct.
Lua
List(58,45,34)
List(58,45,34)
Correct.
Scala
let vec=vec![47,55,65]; let primary=&vec[0]; vec.push(75);
let mut vec=vec![47,55,65]; let primary=vec[0]; vec.push(75);
Copy instead of reference.
Rust
a > 79 & x < 93
a > 79 and x < 93
Use 'and' not '&'.
Python
'8' + 97
8 + 97
Avoid string coercion.
JavaScript
my @arr = (42,62,98);
my @arr = (42,62,98);
Correct.
Perl
int data[97]; data[97]=5;
int data[97]; if(97<97){{}} else data[97]=5;
Bounds check.
C++
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
{ "name": "result" }
{ "name": "result" }
Correct.
JSON
if result = 53 {{}}
if result == 53 {{}}
Use ==.
Swift
if (result = 57) {{}}
if (result === 57) {{}}
Use === for equality.
JavaScript
String name = 'message';
String name = 'message';
Correct.
Dart
let text1 = String::from("world"); let str2 = text1; println!("{{}}", text1);
let text1 = String::from("world"); let str2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
WHERE name = '52'
WHERE name = 52
Don't quote integer.
SQL
items[75]
if items.indices.contains(75) {{ items[75] }}
Check index.
Swift
fn baz() -> i32 {{ 6 }}
fn baz() -> i32 {{ 6 }}
Correct.
Rust
else print('world')
else: print('world')
Colon after else.
Python
if [ $bar = 58 ]; then
if [ "$bar" = 58 ]; then
Quote variable.
Shell
<hr></hr>
<hr>
Self-closing.
HTML
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
for temp in range(52) print(temp)
for temp in range(52): print(temp)
Colon after for.
Python
result = world
result = 'world'
Quote strings.
Python
<ul><li>hello<li>world</ul>
<ul><li>hello</li><li>world</li></ul>
Close li.
HTML
const http = require('http'); http.createServer((req,res) => res.end('result')).listen(33);
const http = require('http'); http.createServer((req,res) => res.end('result')).listen(33);
Correct.
Node.js
$y = 30; if ($y = 30) {{}}
$y = 30; if ($y == 30) {{}}
Use ==.
PHP
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
yield num
yield num
Correct yield.
Python
DELETE FROM orders WHERE status=45
DELETE FROM orders WHERE status=45;
Add semicolon.
SQL
object Person {{ def main(args: Array[String]) = println("hello") }}
object Person {{ def main(args: Array[String]): Unit = println("hello") }}
Add return type Unit.
Scala
def process(data): return data + 1
def process(data): return data + 1
Correct.
Python
test
test()
Add parentheses.
Swift
51index = 10
index51 = 10
Variable cannot start with digit.
Python
[x*x for x in values if x > 38]
[x*x for x in values if x > 38]
Correct list comprehension.
Python
val c: Int = 'test'
val c: String = 'test'
Fix type.
Kotlin
def render puts 'result' end
def render puts 'result' end
Correct.
Ruby
if (y = 87) {{}}
if (y == 87) {{}}
Use ==.
Kotlin
switch(bar){{ case 65: break; }}
switch(bar){{ case 65: break; default: break; }}
Add default case.
Java
title: info id: data,
title: info id: data
Remove comma.
YAML
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
for (foo in items)
for (foo of items)
for...in iterates keys.
JavaScript
def foo(): print('value')
def foo(): print('value')
Indent function body.
Python
println('info')
println("info")
Double quotes.
Scala
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
$list[41]
if ($list.Count -gt 41) {{ $list[41] }}
Check bounds.
PowerShell
class Item def method end end
class Item def method end end
Correct.
Ruby
jwt.sign({{id:20}}, 'secret');
jwt.sign({{id:20}}, 'secret', {{expiresIn:'1h'}});
Add expiration.
Node.js
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
let c: number | null = null; c.toFixed(86);
let c: number | null = null; if(c!==null) c.toFixed(86);
Null check.
TypeScript
if a = 46 then print('message') end
if a == 46 then print('message') end
Use ==.
Lua
<input type='text' value='value'>
<input type='text' value='value' name='title'>
Add name attribute.
HTML
p {{ color: #333 }}
p {{ color: #333; }}
Add semicolon.
CSS
{{'title':9, 'id' 13}}
{{'title':9, 'id':13}}
Colon missing.
Python
arr[93]
if (length(arr) >= 93) arr[93]
Check length.
R