Trying to build menu in C++ that will take functions - c++

Question

I want the program to ask the user to enter a number and then that function in the array will display on the screen
e.g
case 0 = displayNums (displays numbers entered by the user)
case 2 = getAverage (gets average of numbers entered)
I tried to code the menu to do that, but it only shows up. Nothing happens when the number for the specific function is entered.
#include <iostream>
#define integer 12
int ShowMenu(void);
double displayNums(double[], int);
double GetTotal(double[], int);
double getAverage(double[], int);
double getLargest(double[], int, int*);
double getSmallest(double[], int, int*);
int getNumOccurence(double[], int, int n);
double scaleUp(double[], int);
using namespace std;
int main() {
cout << "enter 12 integers 1 by 1:\n";
int data;
int n = 1;
// array to hold the integers
double arr[integer];
// get the integers
for (int i = 0; i < 12; i++) {
cin >> arr[i];
}
int option;
do {
option = ShowMenu();
switch (option) {
case 0:
double displayNums();
break;
case 1:
double GetTotal();
break;
case 2:
double getAverage();
break;
case 3:
double getLargest();
break;
case 4:
double getSmallest();
break;
case 5:
int getNumOccurence();
break;
case 6:
double scaleUp();
break;
case 7:
break;
default:
cout << "invalid option\n";
}
} while (option != 7);
// displays numbers entered by user
cout << displayNums(arr, integer) << endl;
// displays sum of numbers entered
cout << GetTotal(arr, integer) << endl;
// displays the average
cout << "Average integer is:" << getAverage(arr, integer) << endl;
// displays the largest
cout << "Largest integer is: " << getLargest(arr, integer, &data) << endl;
// display the smallest integer
cout << "Smallest integer is:" << getSmallest(arr, integer, &data) << endl;
// display the occurence of the num
cout << "Occurence integer is:" << getNumOccurence(arr, integer, n) << endl;
// display the scale up integers
cout << "Scaled up integers are:" << scaleUp(arr, integer) << endl;
return 0;
}
int ShowMenu(void) {
int option;
cout << "\t0. Display Numbers\n";
cout << "\t1. Get Total of numbers\n";
cout << "\t2. Get Average\n";
cout << "\t3. Get Largest\n";
cout << "\t4. Get Smallest\n";
cout << "\t5. Get Number Occurences\n";
cout << "\t6. Scale Up\n";
cout << "\t7. Quit\n";
cout << "\t\t\tOption ? ";
cin >> option;
return option;
}
double displayNums(double arr[], int size) {
double display = 0;
for (int i = 0; i < size; i++) { // for loop
}
cout << "the numbers that you have entered into the array are:" << endl;
for (int i = 0; i < size; i++) {
cout << arr[i] << endl; // displays numbers entered
}
return display;
}
double GetTotal(double arr[], int size) {
double sum = 0;
for (int i = 0; i < size; i++) {
}
cout << "" << endl;
for (int i = 0; i < 12; i++) {
sum += arr[i];
}
cout << "The sum of all numbers entered is:" << sum << endl;
return sum;
}
double getAverage(double arr[], int size) {
double sum = 0.0, avg;
for (int i = 0; i < size; i++) {
sum = sum + arr[i];
}
avg = sum / size;
return avg;
}
double getLargest(double arr[], int size, int* data) {
double large = 0;
for (int i = 0; i < size; i++) {
if (arr[i] > large) {
large = arr[i];
*data = i + 1;
}
}
return large;
}
double getSmallest(double arr[], int size, int* data) {
double small = 10000;
for (int i = 0; i < size; i++) {
if (arr[i] < small) {
small = arr[i];
*data = i + 1;
}
}
return small;
}
int getNumOccurence(double arr[], int size, int n) {
// only works when you insert repetable number 1
int count = 0;
for (int i = 0; i < size; i++) {
if (n == arr[i]) {
count++;
}
}
return count;
}
double scaleUp(double arr[], int size) {
int factor = 0;
cout << "enter the scale up factor";
cin >> factor;
for (int i = 0; i < size; i++) {
arr[i] *= factor;
cout << arr[i] << endl;
}
return factor;
}

Answer 1

You could use a std::map instead of all those cases.
// Declare a synonym for a function pointer
typedef double (*Function_Pointer)();
// Declare an abbreviation for the map:
typedef std::map<int, Function_Pointer> Function_Display_Table;
// Initialize the function table:
Function_Display_Table display_table;
display_table[0] = display_nums;
display_table[1] = GetTotal;
display_table[2] = getAverage();
//...
// To process your selection:
Function_Pointer fp = display_table.at(selection);
double return_value = fp();
To expand your menu selection, you only have to add rows to the display_table.