Attempting to make a factorial program has ended poorly

[doctorjew]

Hello, I'm trying to teach myself to code and I've always found the best way to learn was through doing. However in my attempt to make a fairly straightforward program(my first) I have clearly done something horribly wrong. Can anyone offer guidance as to what key concept I've messed up?
Thanks :)

#include <iostream>

using namespace std;

int factorial(int f)//int f being the input number to be put through the program
{
    int fac = f;//fac is the output
    int x = f;
    for(x = f; x=0; x-1)//x is to keep track of the loop
    {
        int fac = fac * x;
        cout<<fac;//just to check what is being done(nothing)
    }
    return fac;
}

int main()
{
    int y;
    cin>> y;
    int z = factorial(y);
    cout<< z;
    cin.ignore();
    return 0;
}

[Zhuge]

The last expression in your for loop doesn't do anything. Did you mean x-=1 or --x?

Line 11 creates a new variable called fac each iteration of the loop that is different from the fac on line 7. Just use the fac you declared on line 7 inside the for loop.

[doctorjew]

I've made those changes however the output is now the same as the input.
Thanks for your quick reply!

#include <iostream>

using namespace std;

int factorial(int f)//int f being the input number to be put through the program
{
    int fac = f;//fac is the output
    int x = f;
    for(x = f; x=0; x=x-1)//x is to keep track of the loop
    {
        fac = fac * x;
        cout<<fac;//just to check what is being done(nothing)
    }
}

int main()
{
    int y;
    cin>> y;
    int z = factorial(y);
    cout<< z;
    cin.ignore();
    return 0;
}

[cire]

You aren't returning anything from the function, so what do you expect line 20 to do and line 21 to display?

int factorial( int f )
{
    int result = f ;

    while ( --f > 1 )
        result *= f ;

    return result ;
}

[doctorjew]

I did originally have it returning the value but i wanted to have the cout so i could check if my loop was working.
Why do you not need curly brackets around the while in the example above?

[cire]

You need curly brackets (which indicate a compound statement) only when the block of code you wish to execute consists of multiple statements. If the code you wish to execute for a loop consists of only one statement, the brackets aren't needed, although some folks consider it good practice to include them anyway.

[doctorjew]

Thank you.
One last quick question; I haven't seen the syntax in line 6 what do I need to read up on, as a google search isn't very helpful.

[cire]

result *= f;

is equivalent to:

result = result * f ;

I would strongly suggest buying a book if you're serious about learning C++.

http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list

[doctorjew]

Learning C++ is part of a course I'm taking this semester, but in saying that the course caters for some who really shouldn't be touching a computer so we'll see what happens. Thanks for the advice you've been excellent

[MikeyBoy]

There's another problem in your for statement:

    for(x = f; x=0; x=x-1)//x is to keep track of the loop
//             ^^^
//             Using single '=' sign means assignment, not comparison