I have intensely tried to understand the structure behind Bjarne Stroustrup's calculator (Chapter 6 & 7) from Programming Principles and Practice Using C++, but I can't seem to get through all of it.
So what I did was to try to create my own versions of the calculator. I have roughly created 4 versions of a calculator, slowly progressing. Now, I have somewhat created a parser for the operator and operands. Letting the calculator take inputs such as
2 + 3 * 2 / 4
in one line. Yet, I can't seem to get the order of operations (grammar) to work. As of now, the calculator won't take parentheses or be obedient for the order of operations. Which is something I hope to fix.
So for the actual code. It takes in a left value, an operator and a right value:
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cin >> lval;
while (cin >> op) {
if (op == ';') {
cout << "= " << lval << endl;
keep_window_open();
getchar();
}
cin >> rval;
 
Then it proceeds by a switch case to math the values up with the operator between them.
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switch (op) {
case '+':
lval += rval;
break;
case '':
lval = rval;
break;
// Etc..
 
And after this is where my question lands. How can I replace the switch with something that will interept my want of order of operations? I have looked into recursion, RPN, Bjarne's code and so forth. But I can't seem to get it working without something easier to wrap my head around first.
Here's the full source if someones interested:
https://repl.it/repls/BleakSimilarKestrel