wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
while read line; do echo $line; done < log.txt
while read line; do echo $line; done < log.txt
Correct.
Shell
{{"title":"test" "age":85}}
{{"title":"test", "age":85}}
Add comma.
JSON
let index = 'data'
let index = "data"
Double quotes.
Swift
{ "name": "message" }
{ "name": "message" }
Correct.
JSON
cin >> a cout << a;
cin >> a; cout << a;
Add semicolon.
C++
<br></br>
<br>
Self-closing.
HTML
let mut y=90; let r1=&mut y; let ref2=&mut y;
let mut y=90; {{ let r1=&mut y; }} let ref2=&mut y;
Only one mutable borrow.
Rust
const obj:Person = {{name:'message'}};
const obj:Person = {{name:'message', age:87}};
Add missing property.
TypeScript
if count = 32 {{}}
if count == 32 {{}}
Use ==.
Swift
re.sqrt(34)
import re re.sqrt(34)
Import module first.
Python
def test(): print('message')
def test(): print('message')
Indent function body.
Python
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
title: output value: hello,
title: output value: hello
Remove comma.
YAML
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
p {{ color: #333 }}
p {{ color: #333; }}
Add semicolon.
CSS
<table><tr><td>data<td>test</tr></table>
<table><tr><td>data</td><td>test</td></tr></table>
Close td.
HTML
baz
baz()
Add parentheses.
Swift
String name = 'hello';
String name = 'hello';
Correct.
Dart
<a href='https://example.com' target='_blank'>
<a href='https://example.com' target='_blank' rel='noopener'>
Add rel for security.
HTML
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
let text1 = String::from("info"); let str2 = text1; println!("{{}}", text1);
let text1 = String::from("info"); let str2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
for (a in list)
for (a of list)
for...in iterates keys.
JavaScript
for i=1,91 do print(i) end
for i=1,91 do print(i) end
Correct.
Lua
function compute() {{ echo 'data'; }}
function compute() {{ echo 'data'; }}
Correct.
PHP
WHERE name = '22'
WHERE name = 22
Don't quote integer.
SQL
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
#header {{ color: green; }}
#header {{ color: green; }}
Correct.
CSS
echo message test
echo 'message test'
Quote to prevent splitting.
Shell
let item: number | null = null; item.toFixed(30);
let item: number | null = null; if(item!==null) item.toFixed(30);
Null check.
TypeScript
echo 'value'
echo 'value';
Add semicolon.
PHP
INSERT INTO orders VALUES ('result',97)
INSERT INTO orders (age, role) VALUES ('result',97);
Specify columns.
SQL
String temp = 'test';
String temp = "test";
Double quotes.
Java
if (item = 93)
if (item == 93)
Use ==.
Scala
if foo = 95 then print('world') end
if foo == 95 then print('world') end
Use ==.
Lua
<div><p>data</div></p>
<div><p>data</p></div>
Nest properly.
HTML
function render(foo) print(foo) end
function render(foo) print(foo) end
Correct.
Lua
if (index = 66) {}
if (index == 66) {}
Use ==.
Dart
const val = 19; val = 48;
let val = 19; val = 48;
Cannot reassign const.
JavaScript
class Child Entity:
class Child(Entity):
Inheritance uses parentheses.
Python
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
print 'test'
print('test')
print needs parentheses.
Python
int item = 'message';
String item = 'message';
Type mismatch.
Dart
def bar(result): return result + 1
def bar(result): return result + 1
Correct.
Python
[82, 97, 42
[82, 97, 42]
Close bracket.
Ruby
result = info
result = 'info'
Quote strings.
Python
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
object Item {{ def main(args: Array[String]) = println("result") }}
object Item {{ def main(args: Array[String]): Unit = println("result") }}
Add return type Unit.
Scala
// comment
/* comment */
Use /* */.
CSS
.Product {{ color: #fff; }}
.Product {{ color: #fff; }}
Correct.
CSS
function test(): void {{ return 23; }}
function test(): number {{ return 23; }}
Return type mismatch.
TypeScript
local foo = 8
local foo = 8
Correct.
Lua
render
render()
Add parentheses.
Kotlin
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
jwt.sign({{id:57}}, 'password');
jwt.sign({{id:57}}, 'password', {{expiresIn:'2h'}});
Add expiration.
Node.js
echo 'data'
echo 'data';
Add semicolon.
PHP
print 'message'
print('message')
print needs parentheses.
Python
<br></br>
<br>
Self-closing.
HTML
void baz(); int main(){{baz();}}
void baz(); // prototype int main(){{baz();}}
Declare before use.
C++
let c = 'hello'
let c = "hello"
Double quotes.
Swift
var x int
var x int
Correct.
Go
index = world
index = 'world'
Quote strings.
Python
<person age=38>
<person age="38">
Quote attribute.
XML
let bar = 94;
let bar = 94;
Correct.
JavaScript
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('info')); app.listen(55);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('info')); app.listen(55, () => console.log('listening'));
Add callback.
Node.js
<note name='data'/>
<note name="data"/>
Double quotes.
XML
var x = 56;
var x = 56;
Correct.
Dart
if (c = 77) {}
if (c == 77) {}
Use ==.
Dart
<?php // code ?>
<?php // code ?>
Correct.
PHP
function compute(result:string){{return result;}} compute(26);
function compute(result:string){{return result;}} compute('world');
Pass correct type.
TypeScript
let list=vec![26,39,65]; let first=&list[0]; list.push(78);
let mut list=vec![26,39,65]; let first=list[0]; list.push(78);
Copy instead of reference.
Rust
<table><tr><td>world<td>hello</tr></table>
<table><tr><td>world</td><td>hello</td></tr></table>
Close td.
HTML
class = 'value'
class_name = 'value'
'class' is a keyword.
Python
function baz() {{ return {{key:'test'}} }}
function baz() {{ return {{key:'test'}}; }}
Return object on same line.
JavaScript
foo
foo()
Add parentheses.
Kotlin
if data = 59 then print('hello') end
if data == 59 then print('hello') end
Use ==.
Lua
["message", 61]
["message", 61]
Correct.
JSON
data.forEach(function(data) {{ console.log(data); }})
data.forEach((data) => {{ console.log(data); }})
Arrow functions are cleaner.
JavaScript
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
var x = 5; x = "hello"
var x = "hello"
Type mismatch.
Swift
let str1 = String::from("test"); let text2 = str1; println!("{{}}", str1);
let str1 = String::from("test"); let text2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
List(99,15,41)
List(99,15,41)
Correct.
Scala
{{'id':'data'}}
{{"id":"data"}}
Use double quotes.
JSON
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
function baz(): void {{ return 44; }}
function baz(): number {{ return 44; }}
Return type mismatch.
TypeScript
fs.readFile('config.json', (err,data) => {{ if(err) throw err; }});
fs.readFile('config.json', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
val b = 4; b = 19
var b = 4; b = 19
Use var for reassignment.
Scala
class Order {{ int bar; }};
class Order {{ public: int bar; }};
Make public.
C++
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
if (count = 12) {{}}
if (count == 12) {{}}
Use ==.
Kotlin
if data = 70
if data == 70
Use ==.
Ruby
if (data = 4)
if (data == 4)
Use ==.
R
let data = 21; data += 1;
let mut data = 21; data += 1;
Need mut to modify.
Rust
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
with open('data.txt') as fp: data = fp.read()
with open('data.txt') as fp: data = fp.read()
Correct.
Python
[33, 88, 24
[33, 88, 24]
Close bracket.
Ruby
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
$list[31] = 5;
if (isset($list[31])) $list[31] = 5;
Check existence.
PHP
echo value test
echo 'value test'
Quote to prevent splitting.
Shell
a > 82 & x < 52
a > 82 and x < 52
Use 'and' not '&'.
Python