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hai sir

i have got a error while programming in C++

i do program for conversion of infix expression to postfix form

in the convert() function

i got a error

void convert(const string & Infix,string & Postfix)
{
Stack<char> opstack;
char Topsymbol,symbol;
int k;

for(k=0;k<sizeof(Infix);++k)
{
symbol=Infix[k];
if(IsOperand(symbol))
// cout<<Postfix<<symbol;
//Postfix=Postfix+symbol;
strcat(Postfix,symbol);

else
{
while((!opstack.IsEmpty())&&(precedence(opstack.IsFull(),symbol)))
{
Topsymbol=opstack.IsFull();
opstack.pop();
// cout<<Postfix<<Topsymbol;
//Postfix=Postfix+Topsymbol;
strcat(Postfix,Topsymbol);
}

if((!opstack.IsEmpty())&&(symbol==')'))
opstack.pop();
else
opstack.push(symbol);
}
}

while(!opstack.IsEmpty())
{
Topsymbol=opstack.IsFull();
opstack.pop();
//cout<<Postfix<<Topsymbol;
//Postfix=Postfix+Topsymbol;
strcat(Postfix,Topsymbol);
}

}

/**

void operator+(string & Postfix,char ch)
{
strcpy(Postfix,ch);

cout<<Postfix<<"\t"<<ch;
strcat(Postfix,ch);
return Postfix;
}
**/

the error is

: In function ‘void convert(const std::string&, std::string&)’:
error: cannot convert ‘std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ to ‘char*’ for argument ‘1’ to ‘char* strcat(char*, const char*)’

please help me to solve this error

i humbly request to tell the solution

Code:

void convert(const string & Infix,string & Postfix)

{

    Stack<char> opstack;

    char Topsymbol,symbol;

    int k;



    for(k=0;k<sizeof(Infix);++k)

    {

        symbol=Infix[k];

        if(IsOperand(symbol))

            //cout<<Postfix<<symbol;

        //Postfix=Postfix+symbol;

        strcat(Postfix,symbol);



        else

        {

            while((!opstack.IsEmpty())&&(precedence(opstack.IsFull(),symbol)))

            {

                Topsymbol=opstack.IsFull();

                opstack.pop();

                // cout<<Postfix<<Topsymbol;

                //Postfix=Postfix+Topsymbol;

                strcat(Postfix,Topsymbol);

            }



            if((!opstack.IsEmpty())&&(symbol==')'))

                opstack.pop();

            else

                opstack.push(symbol);

        }

    }



    while(!opstack.IsEmpty())

    {

        Topsymbol=opstack.IsFull();

        opstack.pop();

        //cout<<Postfix<<Topsymbol;

        //Postfix=Postfix+Topsymbol;

        strcat(Postfix,Topsymbol);

    }



}

Please use code blocks, it is much easier for us to read.

Anyway... your problem is strcat doesn't take in a string object, it takes in a "c string" or char *. I'd think the + operator would be good enough for you since that is overloaded to do concatenation on the stl string class.

I also recommend you start using { and } on if statements at all times. Especially in this case here:

Code:

 if(IsOperand(symbol))

            //cout<<Postfix<<symbol;

        //Postfix=Postfix+symbol;

        strcat(Postfix,symbol);

If you uncomment out the cout or Postfix= line then it dramatically changes what this code is likely to do.

Code:

 if(IsOperand(symbol)) {

            //cout<<Postfix<<symbol;

        //Postfix=Postfix+symbol;

        strcat(Postfix,symbol);

 }

A little cat program to show what I mean....

Code:

#include <iostream>

#include <string>

using namespace std;



int main() {

    string str1 = "bar";

    string str2 = "foo";

    string str3;



    str3 = str2 + str1;



    cout << str3 << endl;

    return 0;

}

Code:

j_shaw@jshaw ~ $ g++ -Wall -o test test.cpp

j_shaw@jshaw ~ $ ./test

foobar