First C++ program help (calculator)

Question

I am a beginner to C++ and pretty much programming altogether (besides a little html and css).

I have decided to start my first project for C++.

A friend recommended me trying to make a simple calculator so here is my first shot. Any pointers would be great too! Not sure exactly what I am missing, if anything, but the error I am receiving is:

1>------ Build started: Project: CalculatorFinal, Configuration: Debug Win32 ------
1>  CalculatorFinal.cpp
1>c:\users\ramee\documents\visual studio 2010\projects\calculatorfinal
 \calculatorfinal\calculatorfinal.cpp(32): warning C4102: 'calc' : unreferenced label
1>  CalculatorFinal.vcxproj -> c:\users\ramee\documents\visual studio 2010
\Projects\CalculatorFinal\Debug\CalculatorFinal.exe
========== Build: 1 succeeded, 0 failed, 0 up-to-date, 0 skipped ==========

my code is below (apologize if its not formatted correctly on here. This is my first post :D

  // CalculatorFinal.cpp : Defines the entry point for the console application.
  //

  #include "stdafx.h"       // Including header
  #include <iostream>       // Including ioStream
  using namespace std;      // Namespace

  void calc (double x, double y);
  double result;
  double n1,n2;             // Declaring Variables
  char q,operation;


  int main()                
  { 
   cout<<"Welcome to My Calculator" <<endl; // Outputs welcome message
   cout<<""<<endl;                               // Blank Space
   cout<<"INSTRUCTIONS: Input a mathmatical equation" <<endl; // Outputs instruction            
   cout<<"              EX: 2 + 2" <<endl;       // Outputs instruction
   cout<<""<<endl;                               // Blank Space
   cout<<"Operators:"<<endl;                     // Outputs operation header
   cout<<"For Addition, select '+'"<<endl        // Outputs ADD instruction
   cout<<"For Subtraction, select '-'"<<endl;    // Outputs SUB instruction
   cout<<"For Multiplication, select '*'"<<endl; // Outputs MUL instruction
   cout<<"For Division, select '/'"<<endl;       // Outputs DIV instruction
   cout<<""<<endl;                               // Blank Space
   cout<<"To clear, select 'c'"<<endl;  // Outputs clear instruction
   cout<<"To quit, select 'q'"<<endl;   // Outputs QUIT instruction
   cout<<""<<endl;                                                                  // Blank Space
   cout<<"Input a mathmatical equation"<<endl;                                      // Input instructions
   cin>>n1>>operation>>n2;
   calc:(n1,n2);
   cout<<"The answer is:"<<result<<endl;
   std::cin>>q;             // Input "q" to "quit"
   return 0;}

void calc(double x, double y)                                                       // Operator function
    {            x=n1;
    y=n2;

    switch(operation)                                                           // Operator swtich statement
    {case '+':
        result = x + y;
        break;

    case '-':
        result = x - y;
        break;

    case '*':
        result = x * y;
        break;

    case '/':
        result = x / y;
        break;

    default:
        cout<<"Improper equation. Please input a valid mathmatical equation"<<endl;
        cin>>n1>>operation>>n2;
        calc (n1,n2);
    }

 }

It is only a warning, it should still work. It DID say 1 succeeded build and 0 failed. — Pandacoder, Aug 05 '13 at 00:38
`calc:(n1,n2);` should be `calc(n1,n2);`. The `:` makes `calc` into a label. — andy256, Aug 05 '13 at 00:40
Okay, you are correct it does run, but when I actually try 1+1 or anything for that matter it says the answer is 0 — newbie897, Aug 05 '13 at 00:42
@andy256 Thanks bro! that did it. so crazy a simple thing like that changes everything — newbie897, Aug 05 '13 at 00:49
I would recommend a [book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) instead of trying to piece code together to learn the language and programming in general. — chris, Aug 05 '13 at 01:02
@chris I am actually an accounting student but am adding cs as a minor this year. Just trying to mess around during the summer before school is all. — newbie897, Aug 05 '13 at 01:50
My favorite C++ book is [Starting Out with C++ (Tony Gaddis)] I recommend you declare your variables in [int main()] rather than making them "global". Return values are also helpful. — Static Cast, Aug 05 '13 at 19:13

Static Cast · Accepted Answer · 2013-08-05T01:20:44.967

Here is a calculator program I wrote based off of yours which is much nicer:

#include <iostream>
using namespace std;

//Function prototype
int solve(int, int, char);

int main()
 {
 //Declare variables
 int solution, num1, num2;
 char oper;

 //Output
 cout << "Calculator\n----------\n" << endl;
 cout << "Syntax:\n" << endl;
 cout << "1 + 3\n" << endl;
 cout << "Operators: +, -, *, /\n" << endl;
 cout << "Equation: ";

 //Input
 cin >> num1 >> oper >> num2;

 //Solve and output
 solution = solve(num1, num2, oper);
 cout << "Answer: " << solution << endl;

 //Pause [until enter key] and exit
 cin.ignore(); //Enter key from last cin may be passed, ignore it.
 cin.get();
 return 0;
 }

int solve(int num1, int num2, char oper)
 {
 //Switch oper
 switch(oper)
  {
  case '+':
   return num1 + num2;
  case '-':
   return num1 - num2;
  case '*':
   return num1 * num2;
  case '/':
   return num1 / num2;
  default:
   cout << "\nIncorrect operation!  Try again: ";
   cin >> num1 >> oper >> num2;
   solve(num1, num2, oper);
  }
 }

Here are some things to watch out for, from your last program: 1) Function prototypes do not have function names [i.e void func(int)] 2) Use return values [i.e. return result;] 3) Make sure you have semi-colons.

.

[OLD POST: cout<<"For Addition, select '+'"<;* // Outputs ADD instruction

[No ending semi-colon]

FYI:

std::cin>>q; // Input "q" to "quit"

std:: not required here. (using namespace std;)

(remove colon in calc:(n1,n2);)

--

Your program will work now.]

I'm not sure I agree that a recursive call to solve() inside is a good idea. Shouldn't the call to solve() come from main()? I think main() should control the flow a bit more in your example. Just my opinion, of course. — joebalt, Aug 05 '13 at 01:29
Yes, of course. I would use a while loop to loop until good result; however, this is a design based off of **his** code. — Static Cast, Aug 05 '13 at 01:30
I took your advice or so I think lol. I'd like to post the edited code, do I just edit it above or what? Sorry for the newbie posts guys. — newbie897, Aug 05 '13 at 01:48

score 0 · Answer 2 · answered Aug 05 '13 at 03:43

I wouldn't call this as a C++ program. It is a mistake which almost all amateur C++ programmers make. I would call this as a C style of writing C++ programs. Please don't get me wrong but you need to start thinking in object oriented way so that you can leverage the true power of C++.

I would recommend you to make a C++ class called calculator and think on the design of the class for a bit before starting to code. I would keep methods such as Add, Subtract, Divide and so on as public and other methods as private. This would also give you a chance to enhance the calculator class in future like say adding memory support to it so that it remembers the last operation or result. Start thinking in object oriented way, in order to avoid spaghetti code which is difficult to manage later.

score 0 · Answer 3 · answered Aug 05 '13 at 09:48

I've commented that I have changed from your original source code. and I've checked this code is working on GCC ( G++ ) compiler

Good luck!

#include "stdafx.h"       
#include <iostream>       
using namespace std;     

void calc (double _x, double _y); // CHANGED
double result;
double n1,n2;            
double x,y; // CHANGED
char q,operation;

int main()                
  { 
    cout<<"Welcome to My Calculator" <<endl; 
    cout<<""<<endl;
    cout<<"INSTRUCTIONS: Input a mathmatical equation" <<endl;
    cout<<"              EX: 2 + 2" <<endl;  
    cout<<""<<endl;                              
    cout<<"Operators:"<<endl;                 
    cout<<"For Addition, select '+'"<<endl;      
    cout<<"For Subtraction, select '-'"<<endl;    
    cout<<"For Multiplication, select '*'"<<endl; 
    cout<<"For Division, select '/'"<<endl;       
    cout<<""<<endl;                               
    cout<<"To clear, select 'c'"<<endl;  
    cout<<"To quit, select 'q'"<<endl;   
    cout<<""<<endl;                      
    cout<<"Input a mathmatical equation"<<endl;
    cin>>n1>>operation>>n2;
    calc(n1,n2); // CHANGED
    cout<<"The answer is:"<<result<<endl;
    std::cin>>q;      
    return 0;
 }

void calc(double _x, double _y) // CHANGED
    {            
    x=_x; // CHANGED
    y=_y; // CHANGED
    switch(operation)
    {case '+':
        result = x + y;
        break;
    case '-':
        result = x - y;
        break;
    case '*':
        result = x * y;
        break;
    case '/':
        result = x / y;
        break;
    default:
        cout<<"Improper equation. Please input a valid mathmatical equation"<<endl;
        cin>>x>>operation>>y; // CHANGED
        calc (x,y); // CHANGED
    }
}

score 0 · Answer 4 · edited Sep 28 '14 at 22:12

This is my code,it too long but support more operators

#include "stdafx.h"
#include"iostream"
#include"math.h"
#include"iomanip"
#include <string>
#include <sstream>

using namespace std;
double calc(string mystring);
double calc2(string mystring);
double factoriel(double number);
double root(double num1,double num2);
double dowork(int a,int b,string c);
int main(){
cout<<"***************************************************\n";
cout<<"*                                                 *\n";
cout<<"*                   calculator                    *\n";
cout<<"***************************************************\n\n\n";

string inpstring;
cin >> inpstring;



int length_string=inpstring.length();


double result;
if(abs(calc(inpstring))>abs(calc2(inpstring))){
result=calc(inpstring);
}
else if(abs(calc(inpstring))<=abs(calc2(inpstring))){
result=calc2(inpstring);
}

double s;
     s=3.14;
cout<<"\n"<<"\tresult    :     "<<result<<endl; 


system("pause");
}





double calc(string mystring){
int a=0;//just for switchings
int numberofop=0;
int length_string=mystring.length();

string ops;
string myop;
double param1=0;
double  param2=0;
double  result=0;
string first_inp;
string second_inp;
ops="+-*/^%!R";
    int length_ops=ops.length();

for (int i=0;i<=length_string-1;i++){
    if (i==0){
    if(mystring.substr (0,1)=="-"){
            continue;
        }
    }

    for (int j=0;j<=length_ops-1;j++){

        if (!(mystring.substr (i,1).compare(ops.substr(j,1)))){

            numberofop++;
            if (numberofop==1){
                    myop=ops.substr(j,1);

                    first_inp = mystring.substr (0,i);
                    second_inp = mystring.substr (i+1,length_string-1);

                    stringstream(first_inp) >> param1;
                    stringstream(second_inp) >> param2;


                    if (myop=="+"){
                        a=1;
                        }
                    else if(myop=="-"){
                        a=2;
                    }
                    else if(myop=="*"){
                        a=3;
                    }
                    else if(myop=="/"){
                        a=4;
                    }
                    else if(myop=="^"){
                        a=5;
                    }
                    else if(myop=="%"){
                        a=6;
                    }
                    else if(myop=="!"){
                        a=7;
                    }
                    else if(myop=="R"){
                        a=8;
                    }

            }
        }

    }
 }

switch (a){
            case 1:             
                result=param1+param2;
            break;

            case 2:             
                result=param1-param2;
            break;

            case 3:         
                result=param1*param2;
            break;

            case 4:             
                result=param1/param2;
            break;

            case 5:             
                result= pow(param1,param2);
            break;

            case 6:                     
                result= int(param1)% int(param2);
            break;
            case 7:                     
                result= factoriel(param1);
            break;
            case 8:                     
                result= root(param1,param2);
            break;
}




return result;
}





double factoriel(double a){
    cout<<"enter number      \n";


            double i=a;
            double d=1;
            while(i>1){

            d=d*i;
            i--;
            }
            return d;
}

double root(double num1,double num2){
    double result;
    double reverce;
        reverce=1/num2;
        result=pow(num1,reverce);
return result;
}


double calc2(string mystring){
int a=0;//just for switchings
int numberofop=0;
int length_string=mystring.length();
double pi=3.1415;
double teta;
string ops;
string myop;
double param1=0;
double  param2=0;
double  result=0;
string first_inp;
string second_inp;
ops="logsincostancot";
    int length_ops=ops.length();

for (int i=0;i<=length_string-1;i++){
    if (i==0){
    if(mystring.substr (0,1)=="-"){
            continue;
        }
    }

    for (int j=0;j<=length_ops-1;j++){

        if (!(mystring.substr (i,3).compare(ops.substr(j,3)))){

            numberofop++;
            if (numberofop==1){
                    myop=ops.substr(j,3);


                    second_inp = mystring.substr (i+3,length_string-1);


                    stringstream(second_inp) >> param2;


                    if (myop=="log"){
                        a=1;
                        }
                    else if(myop=="sin"){
                        a=2;
                    }
                    else if(myop=="cos"){
                        a=3;
                    }
                    else if(myop=="tan"){
                        a=4;
                    }
                    else if(myop=="cot"){
                        a=5;
                    }


            }
        }

    }
}

switch (a){
            case 1:             
                result=log(param2);
            break;

            case 2: 
                teta=(double(param2)*pi)/180;
                result=sin(teta);
            break;

            case 3: 
                    teta=(double(param2)*pi)/180;
                result=cos(teta);
            break;

            case 4: 
                teta=(double(param2)*pi)/180;
                result=tanf(teta);
            break;

            case 5:             
                teta=(double(param2)*pi)/180;
                result=1/tanf(teta);
            break;


}

return result;
}
double dowork(int a,int b,string c){
string cut;
cut=c.substr(a,b);
double result;
result=calc(cut);
cout<<"\nresult is    "<<result;

 return result;
}

score 0 · Answer 5 · answered Dec 17 '14 at 17:40

I had coded this simple calculator using c++ so that we can add, subtract, divide or multiple as many numbers as we want. example: 2+3+4-2= and then you will get your answer.

#include <iostream>
#include <conio.h>

using namespace std;

int main()
{
    char c;
    while(true){
        cout << "To solve your math problem you can use this syntex: number(+, -, / or *)number=" << endl;
        cout << "you can use as many number as you want." << endl << endl;

        int n, ans;
        char oper;

        cin >> n;
        ans = n;
        cin >> oper;

        while(oper!='='){

            cin >> n;

            if(oper=='+'){
                ans = ans + n;
            }
            if(oper=='-'){
                ans = ans - n;
            }
            if(oper=='/'){
                ans = ans/n;
            }
            if(oper=='*'){
                ans = ans*n;
            }
            cin >> oper;
        }
        cout << "answer: " << ans << endl << endl;

        cout << "Press esc to exit or press any key to continue." << endl << endl;
        c=getch();
        if(c==27){
            break;
        }
    }
    return 0;
}

score 0 · Answer 6 · answered Mar 13 '16 at 01:46

Here's my take at it, without making a class. Completely new from yours.

#include <iostream>
#include <cstdlib>
using namespace std;

double a, b;
char operation;


int main()
{
    cout << "Welcome to my calculator program.\n";
    cout << "To make a calculation simply use the following operators -> (+           - * /).\n";
    cout << "To exit, simply write an operation but replace the operator     with 'q'. (eg. 2q3).\n";

    while (operation != 'q'){
        cin >> a >> operation >> b;
        if(std::cin.fail()){
            cout << "Input not numerical. Exiting...";
            exit(1);
        }

        switch (operation)
        {
        case '+':
            cout << "  = " << a + b << '\n';
            break;
        case '-':
            cout << "  = " << a - b << '\n';
            break;
        case '*':
            cout << "  = " << a * b << '\n';
            break;
        case ':':
        case '/':
            cout << "  = " << a / b << '\n';
        }
    }
    return 0;
}

First C++ program help (calculator)

6 Answers6