void search_()
{
    int choice,i,c=0;
    char name[20];
    printf("enter the last name of contatct you search for:\n");
    scanf("%s",name);
    system("cls");
    printf("the results:\n");
    for(i=0; i<counter ; i++)
    {
        if(strcmpi(name,person[i].lname)!='\0')
        {
            printf("first name: %s\nlast name: %s\nAddress: %s\nCity: %s\nNumber: %s\n",person[i].fname,person[i].lname,person[i].address,person[i].city,person[i].number);
            c++;
        }
    }
    if(c==0)
        printf("the name doesn't exist.");
}