Some questions on type.

Was reading the other thread on a basic calculator and started making one myself just for some practice. The problem I had was checking for valid types.

Code:

#include <iostream>
#include <string>
#include <math.h>
#include <sstream>

using namespace std;

class calcIt {

    int varA, varB;

    public:

    calcIt() { varA=0; varB=0; };
    int addIt(int addOne, int addTwo) { return (addOne + addTwo); };
    int subIt(int subOne, int subTwo) { return (subOne - subTwo); };
    int mulIt(int mulOne, int mulTwo) { return (mulOne * mulTwo); };
    int divIt(int divOne, int divTwo) { return (divOne / divTwo); };
    int checkNum(int checkN);

};

int calcIt::checkNum(int checkN) {
    if (fmod(checkN, 1) == 0) { return checkN; }
    return -1;
}

int main() {
    int varA, varB, firstW, secondW;
    string varC;
    calcIt c;

    cout << "Enter the calculation to be made ( n +/-* n ) : ";
    getline(cin, varC);
    firstW = varC.find(" ",0);
    secondW = varC.find(" ", (firstW + 1));
    stringstream(varC.substr(0, firstW)) >> varA;
    stringstream(varC.substr(secondW)) >> varB;
    varC = varC.substr((firstW + 1), 1);
    if (( c.checkNum(varA) == -1 ) || ( c.checkNum(varB) == -1)) {
        cout << endl << "Invalid operators!" << endl;
        return 1;
    }
    if (varC == "*") { cout << endl << c.mulIt(varA,varB) << endl; }
    else if(varC == "/") { cout << endl << c.divIt(varA,varB) << endl; }
    else if(varC == "+") { cout << endl << c.addIt(varA,varB) << endl; }
    else if(varC == "-") { cout << endl << c.subIt(varA,varB) << endl; }
    else { cout << endl << "Invalid operator!" << endl; }


    return 0;
}

It works perfectly, but if you pass alpha strings into varA and varB it will still calculate them since the stringstream turns them into int form. This isn't really a problem, but I would rather have it reject alpha chars for these vars.

If a read fails, it will set the failbit. That does mean you can't immediately destroy the stringstream like you do.

Code:

stringstream bob(varC.substr(0, firstW));
bob >> varA;
if (bob.fail()) { //no input }

Alternatively, just
if (bob)
will do.

Would this be better, or should I still error check each line?

Code:

int main() {
    int varA, varB, firstW, secondW;
    string varC;
    calcIt c;

    try {
        cout << "Enter the calculation to be made ( n +/-* n ) : ";
        getline(cin, varC);
        firstW = varC.find(" ",0);
        secondW = varC.find(" ", (firstW + 1));
        stringstream (varC.substr(0, firstW)) >> varA;
        stringstream (varC.substr(secondW)) >> varB;


        varC = varC.substr((firstW + 1), 1);
        if (( c.checkNum(varA) == -1 ) || ( c.checkNum(varB) == -1)) {
            cout << endl << "Invalid operators!" << endl;
            return 1;
        }
        if (varC == "*") { cout << endl << c.mulIt(varA,varB) << endl; }
        else if(varC == "/") { cout << endl << c.divIt(varA,varB) << endl; }
        else if(varC == "+") { cout << endl << c.addIt(varA,varB) << endl; }
        else if(varC == "-") { cout << endl << c.subIt(varA,varB) << endl; }
        else { cout << endl << "Invalid operator!" << endl; }
    }
    catch (exception& e) {
        cout << "Exception: " << e.what() << endl;
        return 1;
    }

    return 0;
}

If I enter a blank string it returns an exception bad_string::substr and exits the programs.

Thought you meant if nothing was entered, but added following based on your suggestion.

Code:

        stringstream in1(varC.substr(0, firstW));
        stringstream in2(varC.substr(secondW));
        in1 >> varA;
        in2 >> varB;
        if ((!in1) || (!in2)) {
            cout << "Error!" << endl;
            return 1;
        }

Works perfectly now. Thank you Tab and El.