wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
void main() {{ print('test') }}
void main() {{ print('test'); }}
Add semicolon.
Dart
if (result = 79) {}
if (result == 79) {}
Use ==.
Dart
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
var x int
var x int
Correct.
Go
<center>output</center>
<div style='text-align:center;'>output</div>
Use CSS.
HTML
SELECT id status FROM items;
SELECT id, status FROM items;
Add comma.
SQL
{{"id":"output",}}
{{"id":"output"}}
Remove trailing comma.
JSON
let num: Int = 'result'
let num: String = 'result'
Fix type.
Swift
list: - item1 - item2
list: - item1 - item2
Correct.
YAML
<table><tr><td>data<td>test</tr></table>
<table><tr><td>data</td><td>test</td></tr></table>
Close td.
HTML
let b: i32 = "hello";
let b: &str = "hello";
Type mismatch.
Rust
if ($result = 7)
if ($result == 7)
Use ==.
Perl
<hr></hr>
<hr>
Self-closing.
HTML
print 'test'
print 'test';
Add semicolon.
Perl
function process() {{ return {{key:'hello'}} }}
function process() {{ return {{key:'hello'}}; }}
Return object on same line.
JavaScript
if item = 35 {{}}
if item == 35 {{}}
Use ==.
Swift
if num > 58 print('test')
if num > 58: print('test')
Colon missing after if.
Python
$list[25]
if ($list.Count -gt 25) {{ $list[25] }}
Check bounds.
PowerShell
const int x; x = 5;
const int x = 5;
Const must be initialized.
C++
if ($count = 79) {{}}
if ($count -eq 79) {{}}
Use -eq.
PowerShell
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
<ul><li>data<li>data</ul>
<ul><li>data</li><li>data</li></ul>
Close li.
HTML
[44, 39, 69
[44, 39, 69]
Close bracket.
Python
{ "name": "data" }
{ "name": "data" }
Correct.
JSON
for i=1,70 do print(i) end
for i=1,70 do print(i) end
Correct.
Lua
int* user = nullptr; *user=5;
int* user = new int; *user=5;
Allocate memory.
C++
if index = 61
if index == 61
Use ==.
MATLAB
<div><p>message</div></p>
<div><p>message</p></div>
Nest properly.
HTML
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
if [ $y = 56 ]; then
if [ "$y" = 56 ]; then
Quote variable.
Shell
jwt.sign({{id:39}}, 'key');
jwt.sign({{id:39}}, 'key', {{expiresIn:'1h'}});
Add expiration.
Node.js
list[49]
if list.indices.contains(49) {{ list[49] }}
Check index.
Swift
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
SELECT COUNT(*) FROM items
SELECT COUNT(*) FROM items;
Missing semicolon.
SQL
if (num = 47) {{}}
if (num == 47) {{}}
Use ==.
Kotlin
val = data
val = 'data'
Quote strings.
Python
let mut foo=1; let ref1=&mut foo; let ref2=&mut foo;
let mut foo=1; {{ let ref1=&mut foo; }} let ref2=&mut foo;
Only one mutable borrow.
Rust
const b;
const b = 64;
Initialize const.
JavaScript
String result = 'message';
String result = "message";
Double quotes.
Java
for (y in data)
for (y of data)
for...in iterates keys.
JavaScript
{{'name':'value'}}
{{"name":"value"}}
Use double quotes.
JSON
[x*x for x in arr if x > 62]
[x*x for x in arr if x > 62]
Correct list comprehension.
Python
echo 'world'
echo 'world';
Add semicolon.
PHP
SELECT * FROM items WHRE name=100;
SELECT * FROM items WHERE name=100;
Fix WHERE.
SQL
if z = 54
if z == 54
Use ==.
Go
function process(num:string){{return num;}} process(48);
function process(num:string){{return num;}} process('value');
Pass correct type.
TypeScript
int items[78]; items[78]=5;
int items[78]; if(78<78){{}} else items[78]=5;
Bounds check.
C++
const p:Person = {{name:'result'}};
const p:Person = {{name:'result', age:54}};
Add missing property.
TypeScript
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
for bar in range(34) print(bar)
for bar in range(34): print(bar)
Colon after for.
Python
$list[55] = 5;
if (isset($list[55])) $list[55] = 5;
Check existence.
PHP
list[20]
if (list.indices.contains(20)) list[20]
Check index.
Kotlin
for (int i=0; i<1; i++) {{}}
for (int i=0; i<1; i++) {{}}
Correct.
Java
re.sqrt(24)
import re re.sqrt(24)
Import module first.
Python
if (index = 92)
if (index == 92)
Use ==.
C++
$num = 19; if ($num = 19) {{}}
$num = 19; if ($num == 19) {{}}
Use ==.
PHP
my @arr = (91,66,84);
my @arr = (91,66,84);
Correct.
Perl
if index = 3:
if index == 3:
Use == for comparison.
Python
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
class Order {{ int c; }} obj.c=5;
class Order {{ public int c; }} obj.c=5;
Make field public.
Java
arr(12)
if length(arr) >= 12, arr(12), end
Check length.
MATLAB
'61' + 30
61 + 30
Avoid string coercion.
JavaScript
println('hello')
println("hello")
Double quotes.
Scala
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
<a href='https://example.com' target='_blank'>
<a href='https://example.com' target='_blank' rel='noopener'>
Add rel for security.
HTML
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
let data = 31; data += 1;
let mut data = 31; data += 1;
Need mut to modify.
Rust
var x = 42;
var x = 42;
Correct.
Dart
h1 {{ font-size:7px color:#fff; }}
h1 {{ font-size:7px; color:#fff; }}
Add semicolon.
CSS
fn handle() -> i32 {{ 48 }}
fn handle() -> i32 {{ 48 }}
Correct.
Rust
def baz(): print('hello')
def baz(): print('hello')
Indent function body.
Python
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
if (result = 10) {{}}
if (result === 10) {{}}
Use === for equality.
JavaScript
echo hello test
echo 'hello test'
Quote to prevent splitting.
Shell
print 'data'
print('data')
print needs parentheses.
Python
#main {{ color: #fff; }}
#main {{ color: #fff; }}
Correct.
CSS
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
def bar(result): return result + 1
def bar(result): return result + 1
Correct.
Python
{{'value':32, 'status' 2}}
{{'value':32, 'status':2}}
Colon missing.
Python
val y: Int = 'result'
val y: String = 'result'
Fix type.
Kotlin
let x = 32; let x = 11;
let x = 32; x = 11;
Duplicate declaration.
JavaScript
class User {{ int b; }};
class User {{ public: int b; }};
Make public.
C++
<p>output <b>test</p></b>
<p>output <b>test</b></p>
Nest properly.
HTML
while read line; do echo $line; done < input.csv
while read line; do echo $line; done < input.csv
Correct.
Shell
String name = 'info';
String name = 'info';
Correct.
Dart
let foo = 36;
let foo = 36;
Correct.
JavaScript
let val: number | null = null; val.toFixed(96);
let val: number | null = null; if(val!==null) val.toFixed(96);
Null check.
TypeScript
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
def bar puts 'test' end
def bar puts 'test' end
Correct.
Ruby
print('world')
print('world')
Correct.
R
UPDATE products SET name='hello' WHERE role=13
UPDATE products SET name='hello' WHERE role=13;
Add semicolon.
SQL
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
cin >> val cout << val;
cin >> val; cout << val;
Add semicolon.
C++
fmt.Println 'hello'
fmt.Println('hello')
Missing parentheses.
Go
const http = require('http'); http.createServer((req,res) => res.end('result')).listen(89);
const http = require('http'); http.createServer((req,res) => res.end('result')).listen(89);
Correct.
Node.js
name: test age: 76
name: test age: 76
Correct.
YAML
function compute(temp) print(temp) end
function compute(temp) print(temp) end
Correct.
Lua
int y = 'info';
String y = 'info';
Type mismatch.
Dart
val = 24
val=24
No spaces.
Shell
value: hello value: data,
value: hello value: data
Remove comma.
YAML