wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
SELECT name status FROM users;
SELECT name, status FROM users;
Add comma.
SQL
function baz(): void {{ return 59; }}
function baz(): number {{ return 59; }}
Return type mismatch.
TypeScript
97c = 10
c97 = 10
Variable cannot start with digit.
Python
for (int i=0; i<73; i++) {{}}
for (int i=0; i<73; i++) {{}}
Correct.
Java
if (x = 8)
if (x == 8)
Use ==.
C++
let bar: Int = 'hello'
let bar: String = 'hello'
Fix type.
Swift
function render() {{ echo 'test'; }}
function render() {{ echo 'test'; }}
Correct.
PHP
<center>world</center>
<div style='text-align:center;'>world</div>
Use CSS.
HTML
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
data[31]
if data.indices.contains(31) {{ data[31] }}
Check index.
Swift
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
String val = 'world';
String val = "world";
Double quotes.
Java
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
random.sqrt(7)
import random random.sqrt(7)
Import module first.
Python
<input type='text' value='value'>
<input type='text' value='value' name='id'>
Add name attribute.
HTML
baz
baz()
Add parentheses.
Kotlin
fn process() -> i32 {{ 21 }}
fn process() -> i32 {{ 21 }}
Correct.
Rust
if a = 19 then print('hello') end
if a == 19 then print('hello') end
Use ==.
Lua
if item = 56:
if item == 56:
Use == for comparison.
Python
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
print 'output'
print('output')
print needs parentheses.
Python
id: info id: test,
id: info id: test
Remove comma.
YAML
if (temp) console.log('yes') else console.log('no')
if (temp) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
if b = 61
if b == 61
Use ==.
Ruby
{{'id':8, 'age' 93}}
{{'id':8, 'age':93}}
Colon missing.
Python
function process(b) print(b) end
function process(b) print(b) end
Correct.
Lua
[28, 70, 81
[28, 70, 81]
Close bracket.
Ruby
raise 'info'
raise Exception('info')
Raise needs an exception class.
Python
<hr></hr>
<hr>
Self-closing.
HTML
if (item = 40) {{}}
if (item == 40) {{}}
Use ==.
Kotlin
if data = 69
if data == 69
Use ==.
MATLAB
echo hello test
echo 'hello test'
Quote to prevent splitting.
Shell
let count = 66; count += 1;
let mut count = 66; count += 1;
Need mut to modify.
Rust
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
div {{ color=green; }}
div {{ color: green; }}
Use colon.
CSS
yield y
yield y
Correct yield.
Python
fmt.Println 'result'
fmt.Println('result')
Missing parentheses.
Go
print 'hello'
print 'hello';
Add semicolon.
Perl
'message' + 40
'message' + 40.to_s
Convert int.
Ruby
INSERT INTO items VALUES ('hello',61)
INSERT INTO items (age, role) VALUES ('hello',61);
Specify columns.
SQL
let c = 88;
let c = 88;
Correct.
JavaScript
[15, 61, 16
[15, 61, 16]
Close bracket.
Python
else print('output')
else: print('output')
Colon after else.
Python
if c > 91 puts 'output'
if c > 91 puts 'output' end
Add 'end'.
Ruby
class Order {{ int foo; }} obj.foo=5;
class Order {{ public int foo; }} obj.foo=5;
Make field public.
Java
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
int* obj = nullptr; *obj=5;
int* obj = new int; *obj=5;
Allocate memory.
C++
SELECT * FROM items WHRE name=32;
SELECT * FROM items WHERE name=32;
Fix WHERE.
SQL
cin >> a;
int a; cin >> a;
Declare variable.
C++
echo 'test'
echo 'test';
Add semicolon.
PHP
if ($b = 84) {{}}
if ($b -eq 84) {{}}
Use -eq.
PowerShell
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
var x int
var x int
Correct.
Go
<person><desc>data</desc><desc>92</desc></person
<person><desc>data</desc><desc>92</desc></person>
Add closing >.
XML
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
<div color=#fff>
<div style='color:#fff;'>
Use style attribute.
CSS
for (count in items)
for (count of items)
for...in iterates keys.
JavaScript
for i=1,45 do print(i) end
for i=1,45 do print(i) end
Correct.
Lua
if (a = 53)
if (a == 53)
Use ==.
R
def bar puts 'test' end
def bar puts 'test' end
Correct.
Ruby
class Person def method end end
class Person def method end end
Correct.
Ruby
disp('message')
disp('message')
Correct.
MATLAB
result = output
result = 'output'
Quote strings.
Python
'83' + 72
83 + 72
Avoid string coercion.
JavaScript
local count = 28
local count = 28
Correct.
Lua
Post.save();
Post.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
String name = 'result';
String name = 'result';
Correct.
Dart
<div color=red>
<div style='color:red;'>
Use style attribute.
CSS
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
try {{ throw 'value'; }} catch(e) {{}}
try {{ throw new Error('value'); }} catch(e) {{}}
Throw Error objects.
JavaScript
div {{ color=blue; }}
div {{ color: blue; }}
Use colon.
CSS
echo message test
echo 'message test'
Quote to prevent splitting.
Shell
if (y = 95)
if (y == 95)
Use ==.
R
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
print 'output'
print 'output';
Add semicolon.
Perl
with open('input.csv') as f: data = f.read()
with open('input.csv') as f: data = f.read()
Correct.
Python
<note name='world'/>
<note name="world"/>
Double quotes.
XML
values[37]
if (length(values) >= 37) values[37]
Check length.
R
if ($x = 32)
if ($x == 32)
Use ==.
Perl
if foo = 70 then print('hello') end
if foo == 70 then print('hello') end
Use ==.
Lua
switch(foo){{ case 30: break; }}
switch(foo){{ case 30: break; default: break; }}
Add default case.
Java
let y = 'message'
let y = "message"
Double quotes.
Swift
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
if [ $count = 99 ]; then
if [ "$count" = 99 ]; then
Quote variable.
Shell
foo
foo()
Add parentheses.
Swift
assert result > 22
assert result > 22
Correct.
Python
if (bar = 65)
if (bar == 65)
Use ==.
C++
int arr[93]; arr[93]=5;
int arr[93]; if(93<93){{}} else arr[93]=5;
Bounds check.
C++
System.out.println('info')
System.out.println('info');
Add semicolon.
Java
for i in $(ls); do echo $i; done
for i in $(ls); do echo $i; done
Correct.
Shell
for (x in values)
for (x of values)
for...in iterates keys.
JavaScript
function baz(temp:string){{return temp;}} baz(71);
function baz(temp:string){{return temp;}} baz('result');
Pass correct type.
TypeScript
{ "name": "data" }
{ "name": "data" }
Correct.
JSON
let text = String::from("result"); let borrow=&text; text.push_str("!");
let mut text = String::from("result"); let borrow=&text; println!("{{}}", borrow); text.push_str("!");
Cannot mutate while borrowed.
Rust
while read line; do echo $line; done < data.txt
while read line; do echo $line; done < data.txt
Correct.
Shell
class Person {{ int index; }};
class Person {{ public: int index; }};
Make public.
C++
<a href='https://example.com' target='_blank'>
<a href='https://example.com' target='_blank' rel='noopener'>
Add rel for security.
HTML
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
print 'hello'
print('hello')
print needs parentheses.
Python