std::logic_error: basic_string::_s_construct null not valid

Question

I am getting std::logic_error: basic_string::_s_construct null not valid in this program. How can I solve that? I already tried a previously posted solution but could not correct it myself.

#include <iostream>
#include <stack>
#include <string>

using namespace std;

int main()
{
     stack<string> s;
     string temp, exp[] = "abc-+de-fg-h+/*";
     string ch1 = 0, ch2 = 0, ch = 0;
     int sizeExp = sizeof(exp)/sizeof(*exp);
     for(int i=0; i < sizeExp ; i++) {
         ch = exp[i];
         if (ch == "*" || ch == "/" || ch == "+" || ch == "-") {
             if (s.empty() && sizeof(temp) != sizeof(exp)) {
                 cout << "Error in Expression." << endl;
             }
             else {
                 if (sizeof(s.top()) != sizeof(char)){
                     ch1 = s.top();
                     s.pop();
                     ch2 = s.top();
                     temp = '(' + ch2 + ')' + exp[i] + '(' + ch1 + ')';
                     s.push(temp);
                 }
                 else {
                     ch1 = s.top();
                     s.pop();
                     ch2 = s.top();
                     temp = ch2 + exp[i] + ch1;
                     s.push(temp);
                 }
             }
         }
         else {
             s.push(exp[i]);
         }
     }
     cout << temp << endl << "Is your Infix Expression for ";
     cout << exp;
     return 0;
}

Answer 1

The issue is with statements of the sort std::string str = 0;. This leads to undefined behaviour. Use std::string str = ""; to create empty strings.

std::string str = 0; resolves to the constructor std::string::string(const char* s, const Allocator& alloc = Allocator()). The behaviour of this constructor is undefined when s is nullptr. Your argument of 0 gets converted to nullptr.