Question

Write a C++ program to run a menu-driven program with the following choices:

1. Compute the factorial of a number
2. Compute the alternating factorial of a number
3. Quit

#include <iostream>
using namespace std;
void getValidUserInputPosNumGT0 (int *a) {

    int num;
    cout << "Enter in a positive number greater than 0... ";
    cin >> *a;
}
long double factorial (int num) {
    int fact = 1;
    while (num > 1) {
        fact *= num;
        num--;
    }
    return fact;
}
long double AlternatingFactorial (int num) {
    int fact = 1;
    while (num < 1) {
        fact *=num;
        num++;
    }
}
int main (){
    int ch;
    int num;
    cout << "Welcome to the playing with numbers program!\n";
    do {
        cout << "1)Compute the factorial of a number\n";
        cout << "2) Compute the alternating factorial of a number\n";
        cout << "3)Quit\n";
        while (true) {
            cout << "Select an option (1..3)..";
            cin >> ch;
            if (ch == 1 || ch == 2 || ch == 3) {
                break;
            }
        }
        switch (ch) {
            case 1:
                getValidUserInputPosNumGT0(&num);
                cout << "Factorial("<<num<<")="<< factorial(num) << endl;
            case 2:
                long double AlternatingFactorial (int num);
                cout << "AlternatingFactorial" << num << AlternatingFactorial(num)<< endl;
        }
    }       while (ch!=3);
    return 0;


}

I've tried to run this and option one works, but the alternating factorial (option 2) won't run.

Answer 1

#include <iostream>
using namespace std;
void getValidUserInputPosNumGT0 (int *a) {

int num;
cout << "Enter in a positive number greater than 0... ";
cin >> *a;
}
long double factorial (int num) {
int fact = 1;
while (num > 1) {
fact *= num;
num--;
}
return fact;
}
long double AlternatingFactorial (int num) {
int res=0;
for(int m=1;m<=num;m++){
if((num-m)%2==0){
res=res+factorial(m);
}
else{
res=res-factorial(m);
}
}
  
return res;
}
int main (){
int ch;
int num;
cout << "Welcome to the playing with numbers program!\n";
do {
cout << "1)Compute the factorial of a number\n";
cout << "2) Compute the alternating factorial of a number\n";
cout << "3)Quit\n";
while (true) {
cout << "Select an option (1..3)..";
cin >> ch;
if (ch == 1 || ch == 2 || ch == 3) {
break;
}
}
switch (ch) {
case 1:
getValidUserInputPosNumGT0(&num);
cout << "Factorial("<<num<<")="<< factorial(num) << endl;
break;
case 2:
getValidUserInputPosNumGT0(&num);
cout << "AlternatingFactorial(" << num <<")="<< AlternatingFactorial(num)<< endl;
}
} while (ch!=3);
return 0;

}

Note:

The return value is not provided in the function AlternatingFactorial(). So it is modified. And the errors in the switch case statements are removed.

Screenshots:

The screenshots are attached below for reference.

Please follow them for output.