Instance object with a array

I'm working in c++ with a class like :

class foo {
int a ;
    foo (){
      a = rand();
    } 
    foo(int b){ a=b }
 };
 int main(){
   foo * array = new foo[10]; //i want to call constructor foo(int b)
  // foo * array = new foo(4)[10]; ????
 }

Please any help , thanks :D

You should first correct your syntax (put ;, make your constructors public etc). Then, you can use uniform initialization in C++11, like

#include <iostream>

class foo {
public:
    int a;
    foo () {
    }
    foo(int b) { a = b; }
};
int main() 
{
    foo * array = new foo[10] {0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
    std::cout << array[2].a << std::endl; // ok, displays 2
    delete[] array;
}

You should try avoiding altogether raw arrays, use std::vector (or std::array), or any other standard container instead. Example:

std::vector<foo> v{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};

or

std::vector v(10, 4); // 10 elements, all initialized with 4

No need do remember to delete memory etc.