c++ math solving is wrong?????? or what [closed]

  c++, math, visual-studio, xcode
#include <iostream>
#include <math.h>
#include <stdio.h>

using namespace std;

int main()

    char x ;
    double c, f{};

    cout << "welcome" << endl ;
    cout << "press C for celcius to far, press F for opposite direction."; 
    cin >> x ;

    if (x == 'C') {
        cout << "enter a value...";
        cin >> c ;
        c = (f - 32) * 5 / 9;
        cout << f << " Fahrenheit." ;

math is wrong for f value i do lots of changing but it doesnt work the other part of this code is working correctly im talking bout the math section what am i doing wrong

Source: Windows Questions C++