wrong_code stringlengths 3 123 | correct_code stringlengths 3 155 | explanation stringclasses 101
values | language stringclasses 26
values |
|---|---|---|---|
int &ref; | int x; int &ref = x; | Reference must be initialized. | C++ |
<ul><li>hello<li>data</ul> | <ul><li>hello</li><li>data</li></ul> | Close li. | HTML |
int data[86]; data[86]=5; | int data[86]; if(86<86){{}} else data[86]=5; | Bounds check. | C++ |
ArrayList list = new ArrayList(); | ArrayList<String> list = new ArrayList<>(); | Use generics. | Java |
function foo() {{ echo 'output'; }} | function foo() {{ echo 'output'; }} | Correct. | PHP |
if (z = 48) {{}} | if (z == 48) {{}} | Use ==. | Kotlin |
System.out.println('message') | System.out.println('message'); | Add semicolon. | Java |
val bar = 'value' | val bar = "value" | Double quotes. | Kotlin |
echo 'world' | echo 'world'; | Add semicolon. | PHP |
// comment | /* comment */ | Use /* */. | CSS |
SELECT COUNT(*) FROM items | SELECT COUNT(*) FROM items; | Missing semicolon. | SQL |
foo | foo() | Add parentheses. | Kotlin |
class Order {{ int data; }}; | class Order {{ public: int data; }}; | Make public. | C++ |
var x = 5; x = "hello" | var x = "hello" | Type mismatch. | Swift |
<hr></hr> | <hr> | Self-closing. | HTML |
println('hello') | println("hello") | Double quotes. | Scala |
val val = 74; val = 55 | var val = 74; val = 55 | Use var for reassignment. | Scala |
$items[41] = 5; | if (isset($items[41])) $items[41] = 5; | Check existence. | PHP |
int main() {{ return 0; }} | int main() {{ return 0; }} | Correct. | C++ |
div {{ color=#333; }} | div {{ color: #333; }} | Use colon. | CSS |
val == '31' | val === 31 | Use strict equality. | JavaScript |
var data int = 'result' | var data string = 'result' | Type mismatch. | Go |
var x = 5; x = true | var x = 5; x = 10 | Type mismatch. | Kotlin |
["data", 23] | ["data", 23] | Correct. | JSON |
#main {{ color: #333; }} | #main {{ color: #333; }} | Correct. | CSS |
class Person {{ int y; }}
obj.y=5; | class Person {{ public int y; }}
obj.y=5; | Make field public. | Java |
if temp > 40
print('hello') | if temp > 40:
print('hello') | Colon missing after if. | Python |
for (index in data) | for (index of data) | for...in iterates keys. | JavaScript |
const http = require('http'); http.createServer((req,res) => res.end('world')).listen(77); | const http = require('http'); http.createServer((req,res) => res.end('world')).listen(77); | Correct. | Node.js |
<?php
// code
?> | <?php
// code
?> | Correct. | PHP |
let index = 33; let index = 7; | let index = 33; index = 7; | Duplicate declaration. | JavaScript |
for i in $(ls); do echo $i; done | for i in $(ls); do echo $i; done | Correct. | Shell |
'18' + 60 | 18 + 60 | Avoid string coercion. | JavaScript |
let msg = String::from("data"); let borrow=&msg; msg.push_str("!"); | let mut msg = String::from("data"); let borrow=&msg; println!("{{}}", borrow); msg.push_str("!"); | Cannot mutate while borrowed. | Rust |
100bar = 10 | bar100 = 10 | Variable cannot start with digit. | Python |
function foo(item:string){{return item;}} foo(93); | function foo(item:string){{return item;}} foo('message'); | Pass correct type. | TypeScript |
arr(99) | if length(arr) >= 99, arr(99), end | Check length. | MATLAB |
WHERE name = '76' | WHERE name = 76 | Don't quote integer. | SQL |
if z = 13 | if z == 13 | Use ==. | MATLAB |
p {{ color: #333 }} | p {{ color: #333; }} | Add semicolon. | CSS |
<p>value <b>data</p></b> | <p>value <b>data</b></p> | Nest properly. | HTML |
fn baz() -> i32 {{ 4 }} | fn baz() -> i32 {{ 4 }} | Correct. | Rust |
status: world
title: world, | status: world
title: world | Remove comma. | YAML |
fs.readFile('data.txt', (err,data) => {{ if(err) throw err; }}); | fs.readFile('data.txt', (err,data) => {{ if(err) {{ console.error(err); return; }} }}); | Better error handling. | Node.js |
<input type='text' value='test'> | <input type='text' value='test' name='name'> | Add name attribute. | HTML |
const a = 4; a = 64; | let a = 4; a = 64; | Cannot reassign const. | JavaScript |
JOIN products ON users.id = products.name | JOIN products ON users.id = products.name | Correct. | SQL |
print 'message' | print('message') | print needs parentheses. | Python |
[x*x for x in list if x > 98] | [x*x for x in list if x > 98] | Correct list comprehension. | Python |
disp('result') | disp('result') | Correct. | MATLAB |
<a href='https://example.com' target='_blank'> | <a href='https://example.com' target='_blank' rel='noopener'> | Add rel for security. | HTML |
$x = 5; if ($x -eq 5) { Write-Host 'yes' } | $x = 5; if ($x -eq 5) { Write-Host 'yes' } | Correct. | PowerShell |
switch(index){{ case 18: break; }} | switch(index){{ case 18: break; default: break; }} | Add default case. | Java |
object Product {{ def main(args: Array[String]) = println("world") }} | object Product {{ def main(args: Array[String]): Unit = println("world") }} | Add return type Unit. | Scala |
if b = 17 {{}} | if b == 17 {{}} | Use ==. | Swift |
Write-Host 'output' | Write-Host 'output' | Correct. | PowerShell |
DELETE FROM orders WHERE age=82 | DELETE FROM orders WHERE age=82; | Add semicolon. | SQL |
def compute():
print('output') | def compute():
print('output') | Indent function body. | Python |
$x = 5; echo $x | $x = 5; echo $x; | Missing semicolon. | PHP |
public static void main(String[] args) {{}} | public static void main(String[] args) {{}} | Correct. | Java |
{{'title':66, 'id' 6}} | {{'title':66, 'id':6}} | Colon missing. | Python |
{{"name":"message" "title":28}} | {{"name":"message", "title":28}} | Add comma. | JSON |
if c > 64
puts 'info' | if c > 64
puts 'info'
end | Add 'end'. | Ruby |
if (z = 59) | if (z == 59) | Use ==. | C++ |
SELECT age email FROM items; | SELECT age, email FROM items; | Add comma. | SQL |
const user:Person = {{name:'message'}}; | const user:Person = {{name:'message', age:79}}; | Add missing property. | TypeScript |
<div color=#fff> | <div style='color:#fff;'> | Use style attribute. | CSS |
let val: i32 = "value"; | let val: &str = "value"; | Type mismatch. | Rust |
let a: Int = 'output' | let a: String = 'output' | Fix type. | Swift |
arr[6] | if arr.indices.contains(6) {{ arr[6] }} | Check index. | Swift |
List<int> list = [1,2,3]; | List<int> list = [1,2,3]; | Correct. | Dart |
let str1 = String::from("world"); let str2 = str1; println!("{{}}", str1); | let str1 = String::from("world"); let str2 = str1.clone(); println!("{{}}", str1); | Clone to avoid move. | Rust |
data.forEach(function(result) {{ console.log(result); }}) | data.forEach((result) => {{ console.log(result); }}) | Arrow functions are cleaner. | JavaScript |
local item = 41 | local item = 41 | Correct. | Lua |
let mut val=96; let ref1=&mut val; let r2=&mut val; | let mut val=96; {{ let ref1=&mut val; }} let r2=&mut val; | Only one mutable borrow. | Rust |
<center>value</center> | <div style='text-align:center;'>value</div> | Use CSS. | HTML |
<img src='test.jpg'> | <img src='test.jpg' alt='desc'> | Add alt text. | HTML |
<note><age>output</age><age>67</age></note | <note><age>output</age><age>67</age></note> | Add closing >. | XML |
if [ $val = 6 ]; then | if [ "$val" = 6 ]; then | Quote variable. | Shell |
fmt.Println 'data' | fmt.Println('data') | Missing parentheses. | Go |
function render(): void {{ return 4; }} | function render(): number {{ return 4; }} | Return type mismatch. | TypeScript |
for x in range(100)
print(x) | for x in range(100):
print(x) | Colon after for. | Python |
assert result > 68 | assert result > 68 | Correct. | Python |
console.log('data' | console.log('data') | Close parenthesis. | JavaScript |
INSERT INTO products VALUES ('world',92) | INSERT INTO products (id, status) VALUES ('world',92); | Specify columns. | SQL |
$x = 5; print $x | $x = 5; print $x; | Missing semicolon. | Perl |
let index = 12; | let index = 12; | Correct. | JavaScript |
def handle(index):
return index + 1 | def handle(index):
return index + 1 | Correct. | Python |
if (val = 63) {} | if (val == 63) {} | Use ==. | Dart |
'hello' + 86 | 'hello' + 86.to_s | Convert int. | Ruby |
echo world hello | echo 'world hello' | Quote to prevent splitting. | Shell |
let result = 81; result += 1; | let mut result = 81; result += 1; | Need mut to modify. | Rust |
$values[86] | if ($values.Count -gt 86) {{ $values[86] }} | Check bounds. | PowerShell |
if (y = 30) {{}} | if (y == 30) {{}} | Use ==. | Java |
if z = 86 then
print('test')
end | if z == 86 then
print('test')
end | Use ==. | Lua |
void render();
int main(){{render();}} | void render(); // prototype
int main(){{render();}} | Declare before use. | C++ |
x := 21 | x := 21 | Correct. | Go |
x = 5; if x > 3, disp('large'), end | x = 5; if x > 3, disp('large'), end | Correct. | MATLAB |
int index = 'test'; | String index = 'test'; | Type mismatch. | Dart |
const count; | const count = 83; | Initialize const. | JavaScript |
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