Question

I have to write these two methods, to print out what is contained within:

ex is an array composed tokenType tk (sorry, trying to save space and avoid posting the whole structs)

Unfortunately, I am getting a compile error that says: error: no match for âoperator[]â in âex[i]â

How can I fix this so it will override <<, so that the second method uses the first?

ostream & operator<< ( ostream & os , const tokenType & tk)
{
    switch (tk.category)
    {
            case TKN_OPRAND:
            os << tk.operand;
            break;
            case TKN_OPRTOR:
            os << tk.symbol;
            break;              
    }
    return os;
}

ostream & operator<< ( ostream & os , const expression & ex)
{   
    tokenType tk;

    for (int i = 0; i < ex.numTokens; i++)
    {
        tk = ex[i];
        os << tk.operand << " ";  //problem line is this one
    }   
    return os;  
}

struct expression
{
    int numTokens ;
    tokenType tokens[MAX_TOKENS_IN_EXPRESSION] ;
    void print() const ;
    int  toPostfix( expression & pfx ) const ;
    int  evalPostfix( int & val ) ;
    expression() { numTokens = 0 ; } ;  // default constructor
} ;

Answer 1

You are very close – you forgot to reference the tokens array, and tried indexing the expression itself. Naturally, the compiler complained, because you do not have a [] overloaded.

This should work:

for (int i = 0; i < ex.numTokens; i++)
{
    tk = ex.tokens[i]; // <<==== Here is the fix
    os << tk.operand << " ";
}