c_new关键字

不知道为什么要用new
      #include <iostream.h>
      int main(int argc, char *argv[])
      {
         int *a=new int[10];
         a[0]=1;
         a[2]=2;

         int i=0;
         for(i;i<10;i++){
            cout<<a[i]<<endl;
         }
         delete a;
         
         char *p=new char[1];
         p[0]='a';

         cout<<*p<<endl;
         delete p;

         double *dou=new double[11];
         dou[2]=1233.30;
         cout<<dou[2]<<endl;

         return 0;
      }