C++ encryption program using array

Question

I am trying to get 4 digits from user in an array and then apply some encryption on it. i have written the function for it but i am having this error: request for member 'length' in 'f', which is of non-class type 'int [4]' Please tell me why i am facing this issue :( Here is my function:

int encryption(int num){
int a;
int b;
int c;
int d;

d= ((num%1000)%100)%10;
c = ((num%1000)%100)/10;
b = (num%1000)/100;
a = num/1000;

a = (a + 7)%10; 
b = (b + 7)%10; 
c = (c + 7)%10;
d = (d + 7)%10;

int f[] = {c,d,a,b};

int finalNumber = 0;
for (int i = 0; i < f.length; i++) 
{
    int num = f[i];
    if (num != 0) 
    {
        while (num > 0) 
        {
            finalNumber *= 10;
            num /= 10;
        }
        finalNumber += f[i];
    } 
    else 
    {
        finalNumber *= 10;
    }
}

return finalNumber;
}

and main is:

int main()
{
cout<<"enter num";
cin>>num;
int enc=encryption(num);
cout<<"encrypted num is"<<enc;


return 0;
}

Possible duplicate of [How do I find the length of an array?](http://stackoverflow.com/questions/4108313/how-do-i-find-the-length-of-an-array) — cadaniluk, Nov 25 '15 at 13:31
C style arrays don't have functions or member variables, so `f.length` is simply wrong syntax. In your case you can write `sizeof(f)` instead. — πάντα ῥεῖ, Nov 25 '15 at 13:33
@Bilal Zafar Use Java instead of C++. What is the problem?:) — Vlad from Moscow, Nov 25 '15 at 13:34
@πάνταῥεῖ yes it works now, but have an warning now " comparison between signed and unsigned integer expressions [-Wsign-compare] " — Devilism, Nov 25 '15 at 13:36
@BilalZafar That's because `sizeof()` returns a `size_t`, just change `for (size_t i = 0; i < sizeof(f); i++) ` — πάντα ῥεῖ, Nov 25 '15 at 13:37
OK, already done this and working !! thanks but another error in main "cin>>num;" "num' was not declared in this scope" , why this ?? just tell me the issue not the correct code :) — Devilism, Nov 25 '15 at 13:39
And I think it would be more profitable to you if you just followed a book or tutorial about C++ rather than trying to write code randomly... — BlackDwarf, Nov 25 '15 at 13:42

C++ encryption program using array

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