#include <iostream>
using namespace std;
char str1[20],str2[20],str3[20];
void myStrcat(char [],char []);
 
void myStrcat(char str1[],char str2[]){
	int c,d;
	 c = 0;
 
   while(str1[c] != '\0') {
      c++;  	
   }
 
   d = 0;
 
   while(str2[d] != '\0'){
      str1[c] = str2[d];
      d++;
      c++;	
   }
 
   str1[c] = '\0';
}
 
 
int main(){
	cout << "Enter first string: " << endl;
	cin >> str1;
	cout << "Enter secound string: " << endl;
	cin >> str2;
	myStrcat(str1,str2);	
	cout << "Result is " << str1 << endl;
}
 

[{"product":"TEST_1","best_selling_product":"305"},{"product":"IPHONE 4S","best_selling_product":"108"}]

  [{"product":"TEST_1","best_selling_product":305},{"product":"IPHONE 4S","best_selling_product":108}] 

  function best_selling_product(){
			$sql = "SELECT product,SUM(sale_detail.amount) AS best_selling_product FROM sale_detail INNER JOIN product ON sale_detail.idproduct = product.idproduct GROUP BY sale_detail.idproduct ORDER BY SUM(sale_detail.amount) DESC LIMIT 0,5"; 
			$result = $this->conexion->conexion->query($sql);
			$array = array();
			while($record = $result->fetch_array(MYSQLI_ASSOC)){
				$array[] = $record;
			}
			return $array;
			$this->conexion->cerrar();
		}
 

$amountArray[$idproduct] += $amount;

 function saveAllSaleDetails($idsale, $sale) {
			$this->conexion->startTransaction();
			$amountArray = [];
			try {
				foreach ($sale as $detail):
					$idproduct = $detail['id'];
					$amount = $detail['amount'];
					$price = $detail['price'];
					$subtotal = $detail['subtotal'];
					$iduser = 1;
					$this->saveSaleDetail($idsale, $idproduct, $amount, $price, $subtotal, $iduser);
					$amountArray[$idproduct] += $amount;
					$stock = $this->product->getProductStock($idproduct);
					$stock = $stock[0][0] - $amountArray[$idproduct];
 
					if ($stock <= 20) {
						$product = $this->product->getProductById($idproduct);
						$message = $product[0][1]." stock is bellow 20.";
						notification::add($message, $idproduct, 'warning', 'product.php');
					}
				endforeach;
 
				$this->conexion->commit();
				$this->conexion->cerrar();
				return true;
 
			} catch (Exception $e) {
				$this->conexion->rollback();
				$this->conexion->cerrar();
				var_dump($e->getMessage());
				return false;
			}
 
		}
 

 
    DELIMITER $$
 
USE `store`$$
 
DROP TRIGGER /*!50032 IF EXISTS */ `updateStatus`$$
 
CREATE
    /*!50017 DEFINER = 'root'@'localhost' */
    TRIGGER `updateStatus` AFTER UPDATE ON `product` 
    FOR EACH ROW BEGIN
	SELECT stock,CASE WHEN stock = 0 THEN UPDATE product SET STATUS = 0;
    END;
$$
 
DELIMITER ;
 

 $brand =  $result->getBrandById($_POST['brand']); 

case 'add_product':
			$result = new brand();
			$code    = trim(stripslashes(htmlspecialchars($_POST['code'])));
			$product = trim(stripslashes(htmlspecialchars($_POST['product'])));
			$brand =  $result->getBrandById($_POST['brand']);
			$price   = trim(stripslashes(htmlspecialchars($_POST['price'])));
			$stock   = trim(stripslashes(htmlspecialchars($_POST['stock'])));
			$newProduct = new product();
			if($newProduct->add($code,$product,$brand,$price,$stock)){
				echo "success";
			}
			else{
				echo "No se registro";
			}
		break;
 
 

function getBrandById($id){
			$sql = "SELECT idbrand,brand FROM brand WHERE idbrand = {$id}";
			$result = $this->conexion->conexion->query($sql);
			$array = array();
			while($record = $result->fetch_array(MYSQL_NUM)){
				//$a = $record;
				//var_dump($a);
				$array[] = $record;
			}
			return $array;
			$this->conexion->cerrar();
		}
	}
 

case 'add_product':
			$result = new brand();
			$newProduct = new product();
			$code    = trim(stripslashes(htmlspecialchars($_POST['code'])));
			$product = trim(stripslashes(htmlspecialchars($_POST['product'])));
			$price   = trim(stripslashes(htmlspecialchars($_POST['price'])));
			$stock   = trim(stripslashes(htmlspecialchars($_POST['stock'])));
			$brand =  $result->getBrandById($_POST['brand']);
			if($newProduct->add($code,$product,$brand,$price,$stock)){
				echo "success";
			}
			else{
				echo "No se registro";
			}
		break;
 

function getBrandById($id){
			$sql = "SELECT idbrand,code_,brand FROM brand where idbrand={$id}"; 
			$result = $this->conexion->conexion->query($sql);
			$array = array();
			while($record = $result->fetch_array(MYSQL_NUM)){
				$array[] = $record;
			}
			return $array;
			$this->conexion->cerrar();
		}
 

como pudiera encontrar las vulnerabilidades y distintos tipos de comandos como 'or 1 = 1 -- #

si la consulta fuera esta   

code=php-brief]   SELECT * FROM users where username = '$variable' and password = '$variable
'

  INSERT INTO product (price,stock,code,product) VALUES('$price','$stock','$code','$product')