C++ Automatic Calculator

[crodino911]

Just try it and let me know what you think!

#include <cstdlib>
#include <iostream>
using namespace std;
float a,c,n;
char b,d;
float addizione(float a, float c){      //Function +
      float m=a+c;
      return(m);
      }
      float sottrazione(float a, float c){  //Function -
            float m=a-c;
            return(m);
            }
            float divisione(float a, float c){    //Function /
                  float m=a/c;
                  return(m);
                  }
                  float moltiplicazione(float a, float c){    //Function *
                        float m=a*c;
                        return(m);
                        }                 
int main()
{
          cin >> a;          // insert first integer
          LOOP:
          cin >> b;        // insert +-/*
          cin >> c;       // insert second integer 
          cin >> d;      // insert =
          cout << a;
          cout << b;
          cout << c;
          cout << d;
          if(d=='=' && b=='+'){
                    n=addizione(a,c);
                    cout << n;
                    a=n;
                    }else if(d=='=' && b=='-'){
                          n=sottrazione(a,c);
                          cout << n;
                          a=n;
                          }else if(d=='=' && b=='/'){
                                n=divisione(a,c);
                                cout << n;
                                a=n;
                                }else if(d=='=' && b=='*'){
                                      n=moltiplicazione(a,c);
                                      cout << n;
                                      a=n;
                                      }
                                      goto LOOP;   /*goes to loop and allows to 
                                                   automatically continue operating*/
          system("pause");
          return 0;
          }
          

[Bazzy]

LOOP:
   //...
goto LOOP;

Using a while or a do-while is better

system("pause"); read http://www.cplusplus.com/forum/articles/7312/

cin >> a;          // insert first integer
LOOP:
cin >> b;        // insert +-/*
cin >> c;       // insert second integer
cin >> d;      // insert =
cout << a;
cout << b;
cout << c;
cout << d;

why is 'a' before the loop? And making the user type '=' is quite odd.
There is no input validation: http://www.cplusplus.com/forum/articles/6046/

float addizione(float a, float c){      //Function +
      float m=a+c;
      return(m);
      }

Can be written like this:

inline float addizione(float a, float c){      //Function +
      return a+c;
      }

[crodino911]

Thank you for all your precious advices. 'a' is before LOOP: because you don't need to reinsert that value since in evrey function (if-else) n(the result of the operation)=a. So you can do
2
+
3
=
5 here you type the next operation for example * wich is 'b'
2 wich is c
=
10 wich is d.
and so on.
As you can see the result takes itself the place of 'a', that's why LOOP: is after 'a'.
Any other advice or consideration?

[crodino911]

I just made some changes, i think it a lot more user-friendly now:

#include <cstdlib>
#include <iostream>
using namespace std;
float a,c,n,m;
char b,d;
inline float addizione(float a, float c){      //Function +
      return m=a+c;
      }
     inline float sottrazione(float a, float c){  //Function -
            return m=a-c;
            }
           inline float divisione(float a, float c){    //Function /
                  return m=a/c;
                  }
                 inline float moltiplicazione(float a, float c){    //Function *
                        return m=a*c;
                        }                 
int main()
{
          cin >> a;     // insert first integer
          LOOP:
          cin >> b;       // insert +-/*
          cin >> c;              // insert second integer     
          cout << a;
          cout << b;
          cout << c;
          if(b=='+'){
                    n=addizione(a,c);
                    cout << "=" << n << "; \n";
                    a=n;
                    }else if(b=='-'){
                          n=sottrazione(a,c);
                          cout << "=" << n << "; \n";
                          a=n;
                          }else if(b=='/'){
                                n=divisione(a,c);
                                cout << "=" << n << "; \n";
                                a=n;
                                }else if(b=='*'){
                                      n=moltiplicazione(a,c);
                                      cout << "=" << n << "; \n";
                                      a=n;
                                      }
                                      goto LOOP;   /*goes to loop and allows to 
                                                   automatically continue operating*/
          system("pause");
          return 0;
          }

I changed the structure of the function as you suggested me; there is no need to press '=' after every operation; you can type the whole calculation in one line and get a less "ugly" output like this:
2+4+5*2/2 (press enter and not '=')
2+4=6;
6+5=11;
11*2=22:
22/2=11;
Looks better?

[kbw]

goto LOOP? Very naughty.

There an example of a calulator in the 1st edition of Stroustup's The C++ Programming Language that uses recursive decent.

[kbw]

See chapter 6 in the current (3rd) edition.

[Bazzy]

The code of that is here: http://www.research.att.com/~bs/dc_command_line.c

[crodino911]

It is quite difficult for me to fully understand the whole code since i started programming in c++ from less than a week. However i don't understand what's the problem with using the goto statement(i apologize for the noob question).

[Bazzy]

Read this: http://en.wikipedia.org/wiki/Goto#Criticism_of_goto_usage

[crodino911]

Alright, i got it.However i'm trying to use a while or do-while instead of the goto statement but i just can't figure out how to do it whithout massive modification of the code.Any idea?

[kbw]

The code is quite a leap to begin with, but if you have an interactive environment like Visual Studio or XCode, you can step thru the program one line at a time. You'll learn quite a lot from it.

The calculator allows to you make simple variable assignements (as in BASIC) and go on to use them in further operations. It's pretty cool.

[crodino911]

Thank you, i'm looking at that right now and i find it really useful!I didn't know it existed even!By the way, what calculator are you talking about?Mine or the one posted in the link?

[kbw]

Stroustup's version. The book will have some useful commentary.

[Bazzy]

However i'm trying to use a while or do-while instead of the goto statement but i just can't figure out how to do it without massive modification of the code.

If you want to add a do-while loop in your code, you don't have to change much things:
replace LOOP: with do{
and goto LOOP; with }while(true);

[crodino911]

Thank you very much, it was right in front of me and i just couldn't see it!