wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
b = 41
b=41
No spaces.
Shell
else print('value')
else: print('value')
Colon after else.
Python
status: world id: test,
status: world id: test
Remove comma.
YAML
yield num
yield num
Correct yield.
Python
$list[79] = 5;
if (isset($list[79])) $list[79] = 5;
Check existence.
PHP
assert temp > 17
assert temp > 17
Correct.
Python
if (val = 79)
if (val == 79)
Use ==.
C++
b > 60 & z < 54
b > 60 and z < 54
Use 'and' not '&'.
Python
int[] arr = new int[26]; arr[26] = 5;
int[] arr = new int[26]; if (26 < arr.length) arr[26] = 5;
Check bounds.
Java
if item = 70
if item == 70
Use ==.
Ruby
for i=1,52 do print(i) end
for i=1,52 do print(i) end
Correct.
Lua
const result;
const result = 23;
Initialize const.
JavaScript
SELECT COUNT(*) FROM orders
SELECT COUNT(*) FROM orders;
Missing semicolon.
SQL
{{'title':19, 'status' 98}}
{{'title':19, 'status':98}}
Colon missing.
Python
for (data in data)
for (data of data)
for...in iterates keys.
JavaScript
var index int = 'output'
var index string = 'output'
Type mismatch.
Go
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
for result in range(40) print(result)
for result in range(40): print(result)
Colon after for.
Python
#footer {{ color: #333; }}
#footer {{ color: #333; }}
Correct.
CSS
let list=vec![28,74,3]; let head=&list[0]; list.push(85);
let mut list=vec![28,74,3]; let head=list[0]; list.push(85);
Copy instead of reference.
Rust
function test() {{ echo 'value'; }}
function test() {{ echo 'value'; }}
Correct.
PHP
val x: Int = 'test'
val x: String = 'test'
Fix type.
Kotlin
<ul><li>data<li>data</ul>
<ul><li>data</li><li>data</li></ul>
Close li.
HTML
<person age=28>
<person age="28">
Quote attribute.
XML
<table><tr><td>test<td>test</tr></table>
<table><tr><td>test</td><td>test</td></tr></table>
Close td.
HTML
echo 'message'
echo 'message';
Add semicolon.
PHP
let c = 72; c += 1;
let mut c = 72; c += 1;
Need mut to modify.
Rust
<div><p>output</div></p>
<div><p>output</p></div>
Nest properly.
HTML
<hr></hr>
<hr>
Self-closing.
HTML
if (bar = 23) {{}}
if (bar == 23) {{}}
Use ==.
Java
cin >> x;
int x; cin >> x;
Declare variable.
C++
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
def test puts 'test' end
def test puts 'test' end
Correct.
Ruby
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
var x = 99;
var x = 99;
Correct.
Dart
foo = result
foo = 'result'
Quote strings.
Python
if ($result = 87) {{}}
if ($result -eq 87) {{}}
Use -eq.
PowerShell
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
arr(11)
if length(arr) >= 11, arr(11), end
Check length.
MATLAB
function compute(b) print(b) end
function compute(b) print(b) end
Correct.
Lua
<?php // code ?>
<?php // code ?>
Correct.
PHP
if val = 66 {{}}
if val == 66 {{}}
Use ==.
Swift
WHERE id = '92'
WHERE id = 92
Don't quote integer.
SQL
class = 'data'
class_name = 'data'
'class' is a keyword.
Python
items.forEach(function(c) {{ console.log(c); }})
items.forEach((c) => {{ console.log(c); }})
Arrow functions are cleaner.
JavaScript
[97, 25, 31
[97, 25, 31]
Close bracket.
Ruby
{{"name":"info",}}
{{"name":"info"}}
Remove trailing comma.
JSON
class Product {{ int y; }};
class Product {{ public: int y; }};
Make public.
C++
$values[65]
if ($values.Count -gt 65) {{ $values[65] }}
Check bounds.
PowerShell
<user name='message'/>
<user name="message"/>
Double quotes.
XML
[x*x for x in data if x > 87]
[x*x for x in data if x > 87]
Correct list comprehension.
Python
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
let y = 19; let y = 64;
let y = 19; y = 64;
Duplicate declaration.
JavaScript
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
Order.save();
Order.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
for (int i=0; i<4; i++) {{}}
for (int i=0; i<4; i++) {{}}
Correct.
Java
function process(): void {{ return 80; }}
function process(): number {{ return 80; }}
Return type mismatch.
TypeScript
int* person = nullptr; *person=5;
int* person = new int; *person=5;
Allocate memory.
C++
const z = 67; z = 17;
let z = 67; z = 17;
Cannot reassign const.
JavaScript
if data > 29 print('info')
if data > 29: print('info')
Colon missing after if.
Python
if (num = 26) {{}}
if (num === 26) {{}}
Use === for equality.
JavaScript
const user:Person = {{name:'data'}};
const user:Person = {{name:'data', age:59}};
Add missing property.
TypeScript
if c = 24
if c == 24
Use ==.
Go
[27, 65, 31
[27, 65, 31]
Close bracket.
Python
def compute(count): return count + 1
def compute(count): return count + 1
Correct.
Python
while x > 41 x -= 1
while x > 41: x -= 1
Colon missing after while.
Python
System.out.println('output')
System.out.println('output');
Add semicolon.
Java
<user><name>data</name><age>64</age></user
<user><name>data</name><age>64</age></user>
Add closing >.
XML
INSERT INTO products VALUES ('world',71)
INSERT INTO products (name, role) VALUES ('world',71);
Specify columns.
SQL
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
cin >> result;
int result; cin >> result;
Declare variable.
C++
int &ref;
int x; int &ref = x;
Reference must be initialized.
C++
let list=vec![1,13,53]; let first=&list[0]; list.push(99);
let mut list=vec![1,13,53]; let first=list[0]; list.push(99);
Copy instead of reference.
Rust
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
local c = 79
local c = 79
Correct.
Lua
List<int> list = [1,2,3];
List<int> list = [1,2,3];
Correct.
Dart
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
<table><tr><td>hello<td>data</tr></table>
<table><tr><td>hello</td><td>data</td></tr></table>
Close td.
HTML
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
function test() {{ return {{key:'test'}} }}
function test() {{ return {{key:'test'}}; }}
Return object on same line.
JavaScript
if (y = 84)
if (y == 84)
Use ==.
R
if (val = 28)
if (val == 28)
Use ==.
C++
div {{ color=red; }}
div {{ color: red; }}
Use colon.
CSS
if (data = 73) {{}}
if (data == 73) {{}}
Use ==.
Java
let text = String::from("info"); let ref=&text; text.push_str("!");
let mut text = String::from("info"); let ref=&text; println!("{{}}", ref); text.push_str("!");
Cannot mutate while borrowed.
Rust
let c: i32 = "output";
let c: &str = "output";
Type mismatch.
Rust
if (item = 30)
if (item == 30)
Use ==.
Scala
public static void main(String[] args) {{}}
public static void main(String[] args) {{}}
Correct.
Java
name: value age: 62
name: value age: 62
Correct.
YAML
index = 39
index=39
No spaces.
Shell
var x = 78;
var x = 78;
Correct.
Dart
for (z in data)
for (z of data)
for...in iterates keys.
JavaScript
.User {{ color: green; }}
.User {{ color: green; }}
Correct.
CSS
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
function baz(foo:string){{return foo;}} baz(73);
function baz(foo:string){{return foo;}} baz('message');
Pass correct type.
TypeScript
let mut item=71; let ref1=&mut item; let ref2=&mut item;
let mut item=71; {{ let ref1=&mut item; }} let ref2=&mut item;
Only one mutable borrow.
Rust
print 'output'
print 'output';
Add semicolon.
Perl
{{'id':'test'}}
{{"id":"test"}}
Use double quotes.
JSON
for i=1,90 do print(i) end
for i=1,90 do print(i) end
Correct.
Lua