C++ Calculator Program v3.0 with Mem Functions

// kalk-02.cpp
//
// Calculator program that runs in console.
// Type M for menu.
//
// This is the original from PSW book Using C++
// I have used it as a basis to learn C++
//
// I have kept is at the following modifications will
// be easier to understand as the program becomes more sophisticated.
//
// Mods
// 01 Change command short cuts to alpha characters so that they are simple to
// key. Trivial change.
// 02 Add extra functions again trivial.
// 03 Add Memory functions
// MEM IN .. loads memory with current value
// MEM PLUS .. adds current value to memory
// Note: Mem Minus achieved by typing n (negative) to make current
// value negative and MEM PLUS. If required redo n to make current
// value positive.
// MEM SWITCH switches current value and memory.
// 03a Added code to change negative current value to positive when
// Power function AND exponent is less than 1 (e.g. 0.5 for square root)
// as even roots of negative numbers are imaginary
// Planned mods
// 04 Add cacpability to use mem value in function, e.g. to subtract value in
// in memory from current value, but keep memory value.
// This was a bit complicated and required writing function to replace CIN
// and use of STRING to DOUBLE function
// 05 Improve by checking that values entered are numbers and not garbage.
// 06 Capability to undo up to last 5 commands. Code with Vector?
// 07 Log comands to file so that they can be audited.
// Have default log KALKLOG.DAT in C:|MyDATA which is backed up to
// KALKLOG.BAK start of new program, overwriting previous version.
// 08 Allow user to change log file name and locaton.
// 09 Take data file in LOG format and run as batch program.
//
// Also plan to use as test for compiling in Linux and with other systems.
// May try to convert to Java and Ruby??
// When I have learned widows programming may try to convert to windows type.
//
// I know it is all old hat but it helps me to learn and may even help others.
//

#include
#include
#include
#include
using namespace std;

void display_menu();
// h/H displays instuctions
// int is_menu_choice(char choice);
void process_choice (char choice, // OUT
double& curr_val, // IN-OUT
double& mem);
int main()
{
char choice; // menu choice
double curr_val; // current value of calculator
double mem; // Calculator Mem function

display_menu();
cout << setprecision(15);
curr_val = 0;
mem = 0;

do {
cin >> choice;
choice = toupper(choice);
process_choice (choice, curr_val, mem);
}
while (choice != 'Q'); // user selects quit
return 0;
}

void display_menu()
{
cout << "Calculator functions:\n"
<< " (A)add, (S)ubtract X(mult), (D)ivide , (N)egative,\n"
<< " (R)eciprocal, (I)nitialize, (P)ower [positive only], Q)uit,\n"
<< " (M)em in, mem p(L)us, mem (O)ut, mem s(W)itch \n"
<< " (H)elp show this menu again.\n\n";
}

void process_choice (char choice, // OUT
double& curr_val, // IN-OUT
double& mem) // IN-OUT

{
double work; // required for memory sWtch function
double num;
switch (choice)
{
case 'A': cin >> num;
curr_val += num;
break;
case 'D': cin >> num;
curr_val = curr_val/num;
break;
case 'H': break;
case 'I': cin >> curr_val;
break;
case 'L': mem += curr_val;
break;
case 'M': mem = curr_val;
break;
case 'N': curr_val *= (-1);
break;
case 'O': curr_val = mem;
break;
case 'P': cin >> num;
if (num < 1) curr_val = fabs(curr_val); //stops possibilty roots of negative values causing errors
curr_val = pow(curr_val, num);
break;
case 'Q': break;
case 'R': curr_val = 1/curr_val;
break;
case 'S': cin >> num;
curr_val -= num;
break;
case 'W': work = curr_val; // switches current and memory values
curr_val = mem;
mem = work;
break;
case 'X': cin >> num;
curr_val *= num;
break;
default: cout << "\tInvalid operation!\n";
} // end switch
if (choice=='H') display_menu();
if (choice != ('Q' || 'H' ))
cout << setw(16) << ' ' << curr_val
<< endl;
}

/*A typical run:

Calculator functions:\n"
(A)add, (S)ubtract X(mult), (D)ivide , (N)egative,\n"
(R)eciprocal, (I)nitialize, (P)ower, Q)uit,\n"
(H)elp show this menu again.\n\n";

I 2.5
2.5
P 3
15.625
R
0.064
x 100
6.4
n
-6.4
a 10
3.6
s 1.12
2.48
H
Calculator functions:\n"
(A)add, (S)ubtract X(mult), (D)ivide , (N)egative,\n"
(R)eciprocal, (I)nitialize, (P)ower, Q)uit,\n"
(H)elp show this menu again.\n\n";

2.48
d 2.5
0.992
i 4
4
p 0.5
2
n
-2
p 0.5
1.4142135623731
i10
10
m
10
r
0.1
w
10
o
0.1
x1000
100
l
100
l
100
o
200.1

q

------------------------

Note you do not need to leave space,
e.g. you can enter "d 2.5" or "d2.5"

*/