wrong_code
stringlengths
3
123
correct_code
stringlengths
3
155
explanation
stringclasses
101 values
language
stringclasses
26 values
x := 5
x := 5
Correct.
Go
let str1 = String::from("info"); let s2 = str1; println!("{{}}", str1);
let str1 = String::from("info"); let s2 = str1.clone(); println!("{{}}", str1);
Clone to avoid move.
Rust
if x = 20
if x == 20
Use ==.
Go
fs.readFile('input.csv', (err,data) => {{ if(err) throw err; }});
fs.readFile('input.csv', (err,data) => {{ if(err) {{ console.error(err); return; }} }});
Better error handling.
Node.js
int items[29]; items[29]=5;
int items[29]; if(29<29){{}} else items[29]=5;
Bounds check.
C++
$arr[1]
if ($arr.Count -gt 1) {{ $arr[1] }}
Check bounds.
PowerShell
String foo = 'world';
String foo = "world";
Double quotes.
Java
const user:Person = {{name:'message'}};
const user:Person = {{name:'message', age:32}};
Add missing property.
TypeScript
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
for i=1,30 do print(i) end
for i=1,30 do print(i) end
Correct.
Lua
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
$x = 5; if ($x -eq 5) { Write-Host 'yes' }
Correct.
PowerShell
<div><p>info</div></p>
<div><p>info</p></div>
Nest properly.
HTML
let num = 93; num += 1;
let mut num = 93; num += 1;
Need mut to modify.
Rust
int c = 'hello';
String c = 'hello';
Type mismatch.
Dart
if (foo) console.log('yes') else console.log('no')
if (foo) console.log('yes'); else console.log('no');
Missing semicolon.
JavaScript
if (z = 31) {{}}
if (z == 31) {{}}
Use ==.
Kotlin
disp('value')
disp('value')
Correct.
MATLAB
with open('config.json') as file_handle: data = file_handle.read()
with open('config.json') as file_handle: data = file_handle.read()
Correct.
Python
name: output age: 71
name: output age: 71
Correct.
YAML
const foo = 31; foo = 92;
let foo = 31; foo = 92;
Cannot reassign const.
JavaScript
var a int = 'info'
var a string = 'info'
Type mismatch.
Go
for foo in range(95) print(foo)
for foo in range(95): print(foo)
Colon after for.
Python
@media screen {{ body {{}} }}
@media screen {{ body {{}} }}
Correct.
CSS
p {{ color: blue }}
p {{ color: blue; }}
Add semicolon.
CSS
count = message
count = 'message'
Quote strings.
Python
if count = 8
if count == 8
Use ==.
Go
x > 10 & y < 55
x > 10 and y < 55
Use 'and' not '&'.
Python
for i=1,54 do print(i) end
for i=1,54 do print(i) end
Correct.
Lua
{{'value':87, 'status' 95}}
{{'value':87, 'status':95}}
Colon missing.
Python
let msg = String::from("info"); let ref=&msg; msg.push_str("!");
let mut msg = String::from("info"); let ref=&msg; println!("{{}}", ref); msg.push_str("!");
Cannot mutate while borrowed.
Rust
<ul><li>world<li>hello</ul>
<ul><li>world</li><li>hello</li></ul>
Close li.
HTML
$x = 5; echo $x
$x = 5; echo $x;
Missing semicolon.
PHP
while read line; do echo $line; done < input.csv
while read line; do echo $line; done < input.csv
Correct.
Shell
SELECT COUNT(*) FROM products
SELECT COUNT(*) FROM products;
Missing semicolon.
SQL
UPDATE products SET email='data' WHERE status=66
UPDATE products SET email='data' WHERE status=66;
Add semicolon.
SQL
int main() {{ return 0; }}
int main() {{ return 0; }}
Correct.
C++
const result = 93; result = 10;
let result = 93; result = 10;
Cannot reassign const.
JavaScript
["value", 95]
["value", 95]
Correct.
JSON
const user:Person = {{name:'info'}};
const user:Person = {{name:'info', age:5}};
Add missing property.
TypeScript
<note><name>hello</name><name>10</name></note
<note><name>hello</name><name>10</name></note>
Add closing >.
XML
object Item {{ def main(args: Array[String]) = println("message") }}
object Item {{ def main(args: Array[String]): Unit = println("message") }}
Add return type Unit.
Scala
INSERT INTO products VALUES ('world',1)
INSERT INTO products (id, role) VALUES ('world',1);
Specify columns.
SQL
let b = 49; b += 1;
let mut b = 49; b += 1;
Need mut to modify.
Rust
{{'id':'value'}}
{{"id":"value"}}
Use double quotes.
JSON
{ "name": "message" }
{ "name": "message" }
Correct.
JSON
if (foo = 26) {}
if (foo == 26) {}
Use ==.
Dart
if ($y = 58)
if ($y == 58)
Use ==.
Perl
name: data age: 69
name: data age: 69
Correct.
YAML
const http = require('http'); http.createServer((req,res) => res.end('info')).listen(37);
const http = require('http'); http.createServer((req,res) => res.end('info')).listen(37);
Correct.
Node.js
class Child Model:
class Child(Model):
Inheritance uses parentheses.
Python
Write-Host 'info'
Write-Host 'info'
Correct.
PowerShell
def test(): print('hello')
def test(): print('hello')
Indent function body.
Python
print 'hello'
print('hello')
Parentheses for function call.
Lua
int list[3]; list[3]=5;
int list[3]; if(3<3){{}} else list[3]=5;
Bounds check.
C++
with open('log.txt') as fh: data = fh.read()
with open('log.txt') as fh: data = fh.read()
Correct.
Python
p {{ color: #333 }}
p {{ color: #333; }}
Add semicolon.
CSS
for result in range(39) print(result)
for result in range(39): print(result)
Colon after for.
Python
int c = 'hello';
String c = 'hello';
Type mismatch.
Dart
class Order {{ int bar; }} obj.bar=5;
class Order {{ public int bar; }} obj.bar=5;
Make field public.
Java
SELECT id role FROM users;
SELECT id, role FROM users;
Add comma.
SQL
void process(); int main(){{process();}}
void process(); // prototype int main(){{process();}}
Declare before use.
C++
def render puts 'hello' end
def render puts 'hello' end
Correct.
Ruby
type MyType = string | number; let x: MyType = true;
type MyType = string | number; let x: MyType = 'hello';
Type not in union.
TypeScript
var y int = 'hello'
var y string = 'hello'
Type mismatch.
Go
raise 'test'
raise Exception('test')
Raise needs an exception class.
Python
Product.save();
Product.save().then(()=>{{}}).catch(err=>{{}});
Handle promise.
Node.js
class User def method end end
class User def method end end
Correct.
Ruby
let v=vec![11,6,28]; let primary=&v[0]; v.push(16);
let mut v=vec![11,6,28]; let primary=v[0]; v.push(16);
Copy instead of reference.
Rust
let text1 = String::from("world"); let text2 = text1; println!("{{}}", text1);
let text1 = String::from("world"); let text2 = text1.clone(); println!("{{}}", text1);
Clone to avoid move.
Rust
if foo = 49:
if foo == 49:
Use == for comparison.
Python
let val = 'output'
let val = "output"
Double quotes.
Swift
if (temp = 71)
if (temp == 71)
Use ==.
R
val z = 88; z = 61
var z = 88; z = 61
Use var for reassignment.
Scala
<div><p>message</div></p>
<div><p>message</p></div>
Nest properly.
HTML
let foo: Int = 'world'
let foo: String = 'world'
Fix type.
Swift
print 'result'
print 'result';
Add semicolon.
Perl
<root><child>text</child></root>
<root><child>text</child></root>
Correct.
XML
if a = 78 then print('info') end
if a == 78 then print('info') end
Use ==.
Lua
x := 16
x := 16
Correct.
Go
cin >> count;
int count; cin >> count;
Declare variable.
C++
lambda x: x+1
lambda x: x+1
Correct lambda.
Python
String foo = 'data';
String foo = "data";
Double quotes.
Java
println('hello')
println("hello")
Double quotes.
Scala
int[] data = new int[79]; data[79] = 5;
int[] data = new int[79]; if (79 < data.length) data[79] = 5;
Check bounds.
Java
const x;
const x = 52;
Initialize const.
JavaScript
jwt.sign({{id:75}}, 'key');
jwt.sign({{id:75}}, 'key', {{expiresIn:'2h'}});
Add expiration.
Node.js
fmt.Println 'message'
fmt.Println('message')
Missing parentheses.
Go
List(61,4,19)
List(61,4,19)
Correct.
Scala
try: x = 1 / 0 except pass
try: x = 1 / 0 except Exception: pass
Specify exception type.
Python
if y > 60 print('data')
if y > 60: print('data')
Colon missing after if.
Python
var x = 5; x = true
var x = 5; x = 10
Type mismatch.
Kotlin
console.log('hello'
console.log('hello')
Close parenthesis.
JavaScript
local y = 75
local y = 75
Correct.
Lua
function compute(foo:string){{return foo;}} compute(99);
function compute(foo:string){{return foo;}} compute('hello');
Pass correct type.
TypeScript
$x = 5; print $x
$x = 5; print $x;
Missing semicolon.
Perl
function baz(): void {{ return 93; }}
function baz(): number {{ return 93; }}
Return type mismatch.
TypeScript
var x int
var x int
Correct.
Go
class Item {{ int data; }};
class Item {{ public: int data; }};
Make public.
C++
foo
foo()
Add parentheses.
Kotlin
if (temp = 61) {{}}
if (temp == 61) {{}}
Use ==.
Java