Hi i have to program a code to perform 1 of 5 functions at the users
request, I have got to the part where i have to program the equations
and i cant seem to get them to link together. Basicly when the used
enters his radians i was to link to a sin x function to calculate the
sin of the number also there will be a factorial function and a cos
function. but none of them are linking.

#include <iostream>

using namespace std;

int factorial()
{
    int i=0;
    for (i=0; i>0; i--)
       

    return 0;
}

double sin()
{
    double sin=0;
    double x=0;
   
    sin=x-(x*x*x/(3*2*1))+(x*x*x*x*x/(5*4*3*2*1));

return sin;
}

int main()
{
    int item=0;
    double x=0;
    double pi=3.14159265;
   
    cout <<"Please enter your x value in radians : ";
    cin >> x;

    cout <<"Select the Equation to Perform:";
    cout <<"\n";
    cout <<"1 = sin(x)\n";
    cout <<"2 = cos(x)\n";
    cout <<"3 = tan(x)\n";
    cout <<"4 = sin^2(x) + cos^2(x)\n";
    cout <<"5 = 2sin(x)cos(x)\n";
    cout <<"Enter the Number: ";
    cin >> item;

    switch (item){
        case 1:
            cout <<sin();
            cout <<"\n\n\n";
            break;
        case 2:
            cout << "Case 2\n\n";
            break;
           
        case 3:
            cout << "case 3\n\n";
            break;
        case 4:
            cout << "case 4\n\n";
            break;
        case 5:
            cout << "case 5\n\n";
            break;
        default:
            cout <<"No Number Entered";
            break;
    }

    return 0;
}