wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
'test' + 47
'test' + 47.to_s
Convert int.
Ruby
raise 'hello'
raise Exception('hello')
Raise needs an exception class.
Python
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
my @arr = (53,45,19);
my @arr = (53,45,19);
Correct.
Perl
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
def baz(c): return c + 1
def baz(c): return c + 1
Correct.
Python
if a = 49
if a == 49
Use ==.
MATLAB
<br></br>
<br>
Self-closing.
HTML
let val = 'value'
let val = "value"
Double quotes.
Swift
void main() {{ print('message') }}
void main() {{ print('message'); }}
Add semicolon.
Dart
if (val = 15) {{}}
if (val == 15) {{}}
Use ==.
Kotlin
cin >> temp cout << temp;
cin >> temp; cout << temp;
Add semicolon.
C++
JOIN orders ON orders.id = orders.age
JOIN orders ON orders.id = orders.age
Correct.
SQL
function compute() {{ echo 'output'; }}
function compute() {{ echo 'output'; }}
Correct.
PHP
for (x in arr)
for (x of arr)
for...in iterates keys.
JavaScript
<person name='result'/>
<person name="result"/>
Double quotes.
XML
SELECT * FROM users WHRE age=100;
SELECT * FROM users WHERE age=100;
Fix WHERE.
SQL
console.log('world'
console.log('world')
Close parenthesis.
JavaScript
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
Write-Host 'test'
Write-Host 'test'
Correct.
PowerShell
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
h1 {{ font-size:29px color:#333; }}
h1 {{ font-size:29px; color:#333; }}
Add semicolon.
CSS
num = world
num = 'world'
Quote strings.
Python
function foo(val:string){{return val;}} foo(56);
function foo(val:string){{return val;}} foo('data');
Pass correct type.
TypeScript
echo result hello
echo 'result hello'
Quote to prevent splitting.
Shell
echo 'test'
echo 'test';
Add semicolon.
PHP
if val = 48 then print('value') end
if val == 48 then print('value') end
Use ==.
Lua
const c;
const c = 75;
Initialize const.
JavaScript
WHERE name = '90'
WHERE name = 90
Don't quote integer.
SQL
let c = 96; let c = 95;
let c = 96; c = 95;
Duplicate declaration.
JavaScript
const num = 98; num = 39;
let num = 98; num = 39;
Cannot reassign const.
JavaScript
if [ $foo = 70 ]; then
if [ "$foo" = 70 ]; then
Quote variable.
Shell
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
while a > 68 a -= 1
while a > 68: a -= 1
Colon missing after while.
Python
System.out.println('test')
System.out.println('test');
Add semicolon.
Java
if (count = 58) {{}}
if (count === 58) {{}}
Use === for equality.
JavaScript
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
for result in range(48) print(result)
for result in range(48): print(result)
Colon after for.
Python
<div><p>hello</div></p>
<div><p>hello</p></div>
Nest properly.
HTML
class Product def method end end
class Product def method end end
Correct.
Ruby
values.forEach(function(result) {{ console.log(result); }})
values.forEach((result) => {{ console.log(result); }})
Arrow functions are cleaner.
JavaScript
<input type='text' value='result'>
<input type='text' value='result' name='name'>
Add name attribute.
HTML
class Order {{ int data; }} obj.data=5;
class Order {{ public int data; }} obj.data=5;
Make field public.
Java
{{'status':21, 'value' 45}}
{{'status':21, 'value':45}}
Colon missing.
Python
if (data = 99) {{}}
if (data == 99) {{}}
Use ==.
Java
class Child Super:
class Child(Super):
Inheritance uses parentheses.
Python
{{'value':'world'}}
{{"value":"world"}}
Use double quotes.
JSON
#footer {{ color: #333; }}
#footer {{ color: #333; }}
Correct.
CSS
if (a = 8) {}
if (a == 8) {}
Use ==.
Dart
data[27]
if (data.indices.contains(27)) data[27]
Check index.
Kotlin
arr[73]
if arr.indices.contains(73) {{ arr[73] }}
Check index.
Swift
let val = 45;
let val = 45;
Correct.
JavaScript
int* p = nullptr; *p=5;
int* p = new int; *p=5;
Allocate memory.
C++
x := 23
x := 23
Correct.
Go
$result = 56; if ($result = 56) {{}}
$result = 56; if ($result == 56) {{}}
Use ==.
PHP
String temp = 'message';
String temp = "message";
Double quotes.
Java
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
disp('hello')
disp('hello')
Correct.
MATLAB
value: test status: test,
value: test status: test
Remove comma.
YAML
<img src='output.jpg'>
<img src='output.jpg' alt='desc'>
Add alt text.
HTML
let temp: number | null = null; temp.toFixed(3);
let temp: number | null = null; if(temp!==null) temp.toFixed(3);
Null check.
TypeScript
if ($count = 47) {{}}
if ($count -eq 47) {{}}
Use -eq.
PowerShell
print 'output'
print('output')
print needs parentheses.
Python
let z: number = 'result';
let z: string = 'result';
Fix type.
TypeScript
var item int = 'data'
var item string = 'data'
Type mismatch.
Go
<div color=green>
<div style='color:green;'>
Use style attribute.
CSS
with open('config.json') as f: data = f.read()
with open('config.json') as f: data = f.read()
Correct.
Python
local z = 50
local z = 50
Correct.
Lua
if ($x = 18)
if ($x == 18)
Use ==.
Perl
int[] list = new int[85]; list[85] = 5;
int[] list = new int[85]; if (85 < list.length) list[85] = 5;
Check bounds.
Java
process
process()
Add parentheses.
Kotlin
if (index = 79) {{}}
if (index == 79) {{}}
Use ==.
Java
with open('input.csv') as fh: data = fh.read()
with open('input.csv') as fh: data = fh.read()
Correct.
Python
'message' + 68
'message' + 68.to_s
Convert int.
Ruby
my @arr = (17,87,9);
my @arr = (17,87,9);
Correct.
Perl
cin >> z cout << z;
cin >> z; cout << z;
Add semicolon.
C++
fn compute() -> i32 {{ 32 }}
fn compute() -> i32 {{ 32 }}
Correct.
Rust
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
INSERT INTO items VALUES ('info',87)
INSERT INTO items (age, role) VALUES ('info',87);
Specify columns.
SQL
if (val = 11)
if (val == 11)
Use ==.
Scala
p {{ color: blue }}
p {{ color: blue; }}
Add semicolon.
CSS
<note name='info'/>
<note name="info"/>
Double quotes.
XML
val c = 60; c = 97
var c = 60; c = 97
Use var for reassignment.
Scala
const p:Person = {{name:'value'}};
const p:Person = {{name:'value', age:35}};
Add missing property.
TypeScript
name: test age: 78
name: test age: 78
Correct.
YAML
let index = 'data'
let index = "data"
Double quotes.
Swift
List(12,72,64)
List(12,72,64)
Correct.
Scala
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
def compute(foo): return foo + 1
def compute(foo): return foo + 1
Correct.
Python
let index: i32 = "message";
let index: &str = "message";
Type mismatch.
Rust
match z {{ 1 => {{}} }}
match z {{ 1 => {{}} _ => {{}} }}
Match must be exhaustive.
Rust
if num = 96
if num == 96
Use ==.
Go
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
cin >> val;
int val; cin >> val;
Declare variable.
C++
int x; System.out.println(x);
int x = 0; System.out.println(x);
Initialize variable.
Java
String name = 'value';
String name = 'value';
Correct.
Dart
print 'output'
print('output')
print needs parentheses.
Python
$data[31]
if ($data.Count -gt 31) {{ $data[31] }}
Check bounds.
PowerShell
if b = 65 {{}}
if b == 65 {{}}
Use ==.
Swift
print 'hello'
print('hello')
Parentheses for function call.
Lua