Dear Fellow C++ Programmers,

I am currently just producing a simple scientific calculator to improve and refresh my memory on some skills (I'm a novice programmer). - I am not sure if what I wrote is legal, such as declaring a function from a class outside of the function (you will see). I tried to space out my coding nicely and added comments where my problems are. If anyone could provide aid I would very much appreciate it - thank you!

Code:
#include <iostream.h>
#include <stdlib.h>
int main() {

//global variables
char choice;
int ammount;
float a;
float b;
float c;
float answer;

//class containing functions to be created...
class op_function; {
op_add();
op_sub();
op_mul();
op_div();
op_sqr();
op_sqr_root();
op_pi();
op_sin();
op_cosin();
op_tan();
op_sci_notate();
op_retansw();
}

          //main menu
          cout << "Scientific Calculator Version 0.1 /n";
          cout << "[01] Addition /n";
          cout << "[02] Subtraction /n";
          cout << "[03] Multiplcation /n";
          cout << "[04] Division /n";
          cout << "[05] Square /n";
          cout << "[06] Square Root /n";
          cout << "[07] Circle /n";
          cout << "[08] Sin - Cosin - Tangent /n";
          cout << "[09] Scientific Notation /n";
          cout << "[10] Formulae /n";
          cout << "[10] About Information /n";
          cout << "Selection # ["

          cin >> choice

          cout << "] /n";

          switch(choice) {

                         //case '01' is the selection for addition
                         //case '01' contains 1 overloaded function
                         case '01':

                              cout << "Addition Version 0.1 /n";
                              cout << "Supported: Three Floating Pnts. /n"
                              cout << "Specify Number Ammount: ";

                              cin >> ammount;

                                  //does this first if statement go with the last else statement?
                                  if (ammount == 1) {
                                     cout << "Cannot Compute Value w/ One Number"; }

                                  if (ammount == 2) {

                                     cout << "Enter Num(1): ";

                                     cin >> a;

                                     cout << "/n";
                                     cout << "Enter Num(2): ";

                                     cin >> b;

                                     //do I specify the decleration here? or in the class structure?
                                     op_function.op_add(float a, float b);

                                     op_function.op_add() {
                                              return a + b; }

                                     answer = op_function.op_add(a, b);

                                     cout << "Answer: = " answer;

                                  else {

                                     cout << "Enter Num(1): ";

                                     cin >> a;

                                     cout << "/n";
                                     cout << "Enter Num(2): ";

                                     cin >> b;

                                     cout << "/n";
                                     cout << "Enter Num(3): ";

                                     cin >> c;

                                     //do I specify this here or in the class structure?
                                     op_function.op_add(float a, float b, float c);

                                     op_function.op_add() {
                                              return a + b + c; }

                                     answer = op_function.op_add(a, b, c);

                                     cout << "Answer: = " answer; }

                                  else {
                                     cout << "Cannot Compute Value w/ One Number"; }

                                  //Rest Is Unfinished
I am trying to maintain clean and professional looking code for my own reference and skill and in situations such as these. I hope it is clear enough to understand - if not, I guess i'll still be tinkering with it.