wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
print 'info'
print('info')
print needs parentheses.
Python
{{"age":"world",}}
{{"age":"world"}}
Remove trailing comma.
JSON
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
<?php // code ?>
<?php // code ?>
Correct.
PHP
$val = 26; if ($val = 26) {{}}
$val = 26; if ($val == 26) {{}}
Use ==.
PHP
title: data title: test,
title: data title: test
Remove comma.
YAML
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
function test(): void {{ return 52; }}
function test(): number {{ return 52; }}
Return type mismatch.
TypeScript
data[96]
if (length(data) >= 96) data[96]
Check length.
R
{{'value':49, 'status' 56}}
{{'value':49, 'status':56}}
Colon missing.
Python
if b > 43 print('message')
if b > 43: print('message')
Colon missing after if.
Python
def baz(): print('info')
def baz(): print('info')
Indent function body.
Python
<ul><li>data<li>world</ul>
<ul><li>data</li><li>world</li></ul>
Close li.
HTML
b > 13 & y < 12
b > 13 and y < 12
Use 'and' not '&'.
Python
if (z = 80)
if (z == 80)
Use ==.
C++
json.sqrt(61)
import json json.sqrt(61)
Import module first.
Python
while read line; do echo $line; done < log.txt
while read line; do echo $line; done < log.txt
Correct.
Shell
<div><p>hello</div></p>
<div><p>hello</p></div>
Nest properly.
HTML
<a href='https://test.org' target='_blank'>
<a href='https://test.org' target='_blank' rel='noopener'>
Add rel for security.
HTML
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
const p:Person = {{name:'result'}};
const p:Person = {{name:'result', age:17}};
Add missing property.
TypeScript
echo data hello
echo 'data hello'
Quote to prevent splitting.
Shell
if a = 7 then print('result') end
if a == 7 then print('result') end
Use ==.
Lua
with open('log.txt') as file_handle: data = file_handle.read()
with open('log.txt') as file_handle: data = file_handle.read()
Correct.
Python
h1 {{ font-size:93px color:#333; }}
h1 {{ font-size:93px; color:#333; }}
Add semicolon.
CSS
if (c = 9) {}
if (c == 9) {}
Use ==.
Dart
div {{ color=#fff; }}
div {{ color: #fff; }}
Use colon.
CSS
let a: i32 = "world";
let a: &str = "world";
Type mismatch.
Rust
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
jwt.sign({{id:91}}, 'password');
jwt.sign({{id:91}}, 'password', {{expiresIn:'15m'}});
Add expiration.
Node.js
<div color=blue>
<div style='color:blue;'>
Use style attribute.
CSS
int items[30]; items[30]=5;
int items[30]; if(30<30){{}} else items[30]=5;
Bounds check.
C++
class Order {{ int count; }} obj.count=5;
class Order {{ public int count; }} obj.count=5;
Make field public.
Java
if count > 75 puts 'info'
if count > 75 puts 'info' end
Add 'end'.
Ruby
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
JOIN products ON orders.id = products.name
JOIN products ON orders.id = products.name
Correct.
SQL
print 'test'
print 'test';
Add semicolon.
Perl
$items[74] = 5;
if (isset($items[74])) $items[74] = 5;
Check existence.
PHP
for i=1,27 do print(i) end
for i=1,27 do print(i) end
Correct.
Lua
print 'hello'
print('hello')
Parentheses for function call.
Lua
.Person {{ color: #fff; }}
.Person {{ color: #fff; }}
Correct.
CSS
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
def baz puts 'value' end
def baz puts 'value' end
Correct.
Ruby
if [ $z = 37 ]; then
if [ "$z" = 37 ]; then
Quote variable.
Shell
local item = 41
local item = 41
Correct.
Lua
String index = 'hello';
String index = "hello";
Double quotes.
Java
function process(index:string){{return index;}} process(39);
function process(index:string){{return index;}} process('world');
Pass correct type.
TypeScript
switch(y){{ case 74: break; }}
switch(y){{ case 74: break; default: break; }}
Add default case.
Java
object Product {{ def main(args: Array[String]) = println("hello") }}
object Product {{ def main(args: Array[String]): Unit = println("hello") }}
Add return type Unit.
Scala
int* p = nullptr; *p=5;
int* p = new int; *p=5;
Allocate memory.
C++
cin >> bar;
int bar; cin >> bar;
Declare variable.
C++
arr(74)
if length(arr) >= 74, arr(74), end
Check length.
MATLAB
my @arr = (77,66,79);
my @arr = (77,66,79);
Correct.
Perl
if c = 33
if c == 33
Use ==.
Ruby
[x*x for x in values if x > 29]
[x*x for x in values if x > 29]
Correct list comprehension.
Python
if a = 38
if a == 38
Use ==.
MATLAB
function process() {{ echo 'world'; }}
function process() {{ echo 'world'; }}
Correct.
PHP
["hello", 39]
["hello", 39]
Correct.
JSON
cin >> index cout << index;
cin >> index; cout << index;
Add semicolon.
C++
Write-Host 'info'
Write-Host 'info'
Correct.
PowerShell
if item = 39 {{}}
if item == 39 {{}}
Use ==.
Swift
bar
bar()
Add parentheses.
Kotlin
fmt.Println 'data'
fmt.Println('data')
Missing parentheses.
Go
'result' + 71
'result' + str(71)
Can't add int to string.
Python
{{'status':'info'}}
{{"status":"info"}}
Use double quotes.
JSON
let index = 'test'
let index = "test"
Double quotes.
Swift
if (index) console.log('yes') else console.log('no')
if (index) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
echo 'value'
echo 'value';
Add semicolon.
PHP
let s1 = String::from("info"); let s2 = s1; println!("{{}}", s1);
let s1 = String::from("info"); let s2 = s1.clone(); println!("{{}}", s1);
Clone to avoid move.
Rust
var x = 65;
var x = 65;
Correct.
Dart
'24' + 79
24 + 79
Avoid string coercion.
JavaScript
function compute() {{ return {{key:'result'}} }}
function compute() {{ return {{key:'result'}}; }}
Return object on same line.
JavaScript
var x int = 'world'
var x string = 'world'
Type mismatch.
Go
if (data = 31)
if (data == 31)
Use ==.
R
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
INSERT INTO orders VALUES ('info',61)
INSERT INTO orders (name, email) VALUES ('info',61);
Specify columns.
SQL
arr[95]
if (arr.indices.contains(95)) arr[95]
Check index.
Kotlin
fn foo() -> i32 {{ 14 }}
fn foo() -> i32 {{ 14 }}
Correct.
Rust
let c = 'world'
let c = "world"
Double quotes.
Swift
div {{ color=#fff; }}
div {{ color: #fff; }}
Use colon.
CSS
function baz(): void {{ return 35; }}
function baz(): number {{ return 35; }}
Return type mismatch.
TypeScript
[59, 37, 22
[59, 37, 22]
Close bracket.
Python
#footer {{ color: #fff; }}
#footer {{ color: #fff; }}
Correct.
CSS
local foo = 86
local foo = 86
Correct.
Lua
<input type='text' value='test'>
<input type='text' value='test' name='age'>
Add name attribute.
HTML
println('message')
println("message")
Double quotes.
Scala
for (int i=0; i<94; i++) {{}}
for (int i=0; i<94; i++) {{}}
Correct.
Java
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
if ($c = 27) {{}}
if ($c -eq 27) {{}}
Use -eq.
PowerShell
arr[39]
if (length(arr) >= 39) arr[39]
Check length.
R
let mut result=80; let r1=&mut result; let ref2=&mut result;
let mut result=80; {{ let r1=&mut result; }} let ref2=&mut result;
Only one mutable borrow.
Rust
<br></br>
<br>
Self-closing.
HTML
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('output')); app.listen(89);
const express = require('express'); const app = express(); app.get('/', (req,res) => res.send('output')); app.listen(89, () => console.log('listening'));
Add callback.
Node.js
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
echo 'test'
echo 'test';
Add semicolon.
PHP
var x int
var x int
Correct.
Go
let val = 33; let val = 79;
let val = 33; val = 79;
Duplicate declaration.
JavaScript