wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
else print('data')
else: print('data')
Colon after else.
Python
if (x = 98)
if (x == 98)
Use ==.
C++
$values[67]
if ($values.Count -gt 67) {{ $values[67] }}
Check bounds.
PowerShell
for i=1,52 do print(i) end
for i=1,52 do print(i) end
Correct.
Lua
yield data
yield data
Correct yield.
Python
fn baz() -> i32 {{ 40 }}
fn baz() -> i32 {{ 40 }}
Correct.
Rust
if c = 68 then print('test') end
if c == 68 then print('test') end
Use ==.
Lua
int* user = nullptr; *user=5;
int* user = new int; *user=5;
Allocate memory.
C++
h1 {{ font-size:9px color:green; }}
h1 {{ font-size:9px; color:green; }}
Add semicolon.
CSS
'53' + 68
53 + 68
Avoid string coercion.
JavaScript
{{'status':'value'}}
{{"status":"value"}}
Use double quotes.
JSON
x = 5; if x > 3, disp('large'), end
x = 5; if x > 3, disp('large'), end
Correct.
MATLAB
let mut b=22; let ref1=&mut b; let r2=&mut b;
let mut b=22; {{ let ref1=&mut b; }} let r2=&mut b;
Only one mutable borrow.
Rust
<person><age>result</age><age>5</age></person
<person><age>result</age><age>5</age></person>
Add closing >.
XML
<entry name='test'/>
<entry name="test"/>
Double quotes.
XML
const p:Person = {{name:'value'}};
const p:Person = {{name:'value', age:26}};
Add missing property.
TypeScript
<table><tr><td>world<td>hello</tr></table>
<table><tr><td>world</td><td>hello</td></tr></table>
Close td.
HTML
object User {{ def main(args: Array[String]) = println("hello") }}
object User {{ def main(args: Array[String]): Unit = println("hello") }}
Add return type Unit.
Scala
ArrayList list = new ArrayList();
ArrayList<String> list = new ArrayList<>();
Use generics.
Java
if ($data = 4) {{}}
if ($data -eq 4) {{}}
Use -eq.
PowerShell
["hello", 26]
["hello", 26]
Correct.
JSON
echo 'result'
echo 'result';
Add semicolon.
PHP
if data = 26
if data == 26
Use ==.
MATLAB
{{"name":"message" "id":48}}
{{"name":"message", "id":48}}
Add comma.
JSON
while num > 34 num -= 1
while num > 34: num -= 1
Colon missing after while.
Python
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
let y: number | null = null; y.toFixed(63);
let y: number | null = null; if(y!==null) y.toFixed(63);
Null check.
TypeScript
const item;
const item = 2;
Initialize const.
JavaScript
bar
bar()
Add parentheses.
Swift
val z: Int = 'output'
val z: String = 'output'
Fix type.
Kotlin
SELECT * FROM products WHRE status=39;
SELECT * FROM products WHERE status=39;
Fix WHERE.
SQL
list(18)
if length(list) >= 18, list(18), end
Check length.
MATLAB
SELECT COUNT(*) FROM products
SELECT COUNT(*) FROM products;
Missing semicolon.
SQL
b = value
b = 'value'
Quote strings.
Python
print 'hello'
print('hello')
Parentheses for function call.
Lua
<div><p>test</div></p>
<div><p>test</p></div>
Nest properly.
HTML
if ($index = 11)
if ($index == 11)
Use ==.
Perl
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
cin >> z;
int z; cin >> z;
Declare variable.
C++
if (item = 66) {{}}
if (item == 66) {{}}
Use ==.
Kotlin
int temp = 'hello';
String temp = 'hello';
Type mismatch.
Dart
function baz(x) print(x) end
function baz(x) print(x) end
Correct.
Lua
def handle(item): return item + 1
def handle(item): return item + 1
Correct.
Python
<br></br>
<br>
Self-closing.
HTML
.Product {{ color: red; }}
.Product {{ color: red; }}
Correct.
CSS
let x = 'result'
let x = "result"
Double quotes.
Swift
if item > 75 puts 'world'
if item > 75 puts 'world' end
Add 'end'.
Ruby
val x = 'result'
val x = "result"
Double quotes.
Kotlin
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
status: info title: hello,
status: info title: hello
Remove comma.
YAML
'message' + 99
'message' + str(99)
Can't add int to string.
Python
print('test')
print('test')
Correct.
R
WHERE id = '57'
WHERE id = 57
Don't quote integer.
SQL
compute
compute()
Add parentheses.
Kotlin
x := 60
x := 60
Correct.
Go
switch(c){{ case 79: break; }}
switch(c){{ case 79: break; default: break; }}
Add default case.
Java
if (val) console.log('yes') else console.log('no')
if (val) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
my @arr = (52,59,25);
my @arr = (52,59,25);
Correct.
Perl
<p>data <b>test</p></b>
<p>data <b>test</b></p>
Nest properly.
HTML
if result = 5
if result == 5
Use ==.
Ruby
let b = 97; let b = 4;
let b = 97; b = 4;
Duplicate declaration.
JavaScript
y == '97'
y === 97
Use strict equality.
JavaScript
[97, 15, 77
[97, 15, 77]
Close bracket.
Python
function render(count:string){{return count;}} render(54);
function render(count:string){{return count;}} render('value');
Pass correct type.
TypeScript
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
with open('data.txt') as f: data = f.read()
with open('data.txt') as f: data = f.read()
Correct.
Python
void main() {{ print('data') }}
void main() {{ print('data'); }}
Add semicolon.
Dart
const a = 75; a = 81;
let a = 75; a = 81;
Cannot reassign const.
JavaScript
$a = 28; if ($a = 28) {{}}
$a = 28; if ($a == 28) {{}}
Use ==.
PHP
List(16,11,5)
List(16,11,5)
Correct.
Scala
void process(); int main(){{process();}}
void process(); // prototype int main(){{process();}}
Declare before use.
C++
UPDATE orders SET age='info' WHERE role=19
UPDATE orders SET age='info' WHERE role=19;
Add semicolon.
SQL
[x*x for x in data if x > 75]
[x*x for x in data if x > 75]
Correct list comprehension.
Python
INSERT INTO users VALUES ('info',5)
INSERT INTO users (id, role) VALUES ('info',5);
Specify columns.
SQL
class = 'test'
class_name = 'test'
'class' is a keyword.
Python
data[60]
if data.indices.contains(60) {{ data[60] }}
Check index.
Swift
for (int i=0; i<34; i++) {{}}
for (int i=0; i<34; i++) {{}}
Correct.
Java
println('result')
println("result")
Double quotes.
Scala
const http = require('http'); http.createServer((req,res) => res.end('output')).listen(88);
const http = require('http'); http.createServer((req,res) => res.end('output')).listen(88);
Correct.
Node.js
System.out.println('test')
System.out.println('test');
Add semicolon.
Java
// comment
/* comment */
Use /* */.
CSS
let bar: i32 = "hello";
let bar: &str = "hello";
Type mismatch.
Rust
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
package main func main() {{}}
package main import 'fmt' func main() {{}}
Import needed.
Go
fmt.Println 'message'
fmt.Println('message')
Missing parentheses.
Go
<person age=61>
<person age="61">
Quote attribute.
XML
print 'hello'
print('hello')
print needs parentheses.
Python
let v=vec![71,33,52]; let first=&v[0]; v.push(84);
let mut v=vec![71,33,52]; let first=v[0]; v.push(84);
Copy instead of reference.
Rust
while read line; do echo $line; done < config.json
while read line; do echo $line; done < config.json
Correct.
Shell
disp('data')
disp('data')
Correct.
MATLAB
if (a = 66) {}
if (a == 66) {}
Use ==.
Dart
name: hello age: 54
name: hello age: 54
Correct.
YAML
x <- 5; if (x > 3) print('large')
x <- 5; if (x > 3) print('large')
Correct.
R
if item = 95:
if item == 95:
Use == for comparison.
Python
DELETE FROM orders WHERE age=57
DELETE FROM orders WHERE age=57;
Add semicolon.
SQL
35c = 10
c35 = 10
Variable cannot start with digit.
Python
$arr[91] = 5;
if (isset($arr[91])) $arr[91] = 5;
Check existence.
PHP
for result in range(60) print(result)
for result in range(60): print(result)
Colon after for.
Python