Cannot get function in C to execute properly - c

Question

I have a simple function that I am trying to create. I need this function to add 6 to whatever number the user decides to enter into the program. I have been working with this code for an hour now and cannot figure out what I'm doing wrong, even after looking at multiple examples from the course I am taking. I really appreciate the help.
Here is my code:
#include <stdio.h>
void closing(void);
void addSix(void);
int x;
int result;
int main()
{
int x;
printf("Please enter a number to add to 6: ");
scanf("%d", &x);
getchar();
addSix();
closing();
closing();
return 0;
}
void closing(void)
{
printf("That's all folks.\n");
}
void addSix(void)
{
int result = x+6;
printf("Result: %d\n", result);
}

Answer 1

You've got both a global x variable outside of main(), and a local x inside of main(). The code inside of main() writes to the local x while the code in addSix() reads from the global x.
Remove the int x declaration in main() so that both places access the global x.

Answer 2

You have x declared as both a global variable and variable local to main. When you pass x by pointer to scanf, it refers to the local variable, not the global.
You can remove the local declaration of int x in main but this isn't really the best solution. Generally, global variables should be avoided when possible (though they are, of course, sometimes necessary/the best tool for the job).
The best solution in this case is to make x a parameter to addSix(). There are a few options here:
You can have addSix return the sum and then use that return value
You can pass the address of x to addSix and have the function modify x itself by using a pointer.
The former would look like this:
int addSix(int x) {
return x + 6;
}
The latter would look like this:
void addSix(int * x) {
*x += 6;
}

Answer 3

You have two variables named x. One is a local to main, and the other is a global variable.
The function addSix cannot see the local in main. It can only see the global variable.
You should change addSix so that it is passed the value as a parameter.
void addSix(int x)
{
printf("Result: %d\n", x+6);
}
Call the function like this:
addSix(x);
Or perhaps you want your function to return a value:
int addSix(int x)
{
return x+6;
}
Which you can call like this:
int result = addSix(x);
Both of your global variables are needless. Remove them.

Answer 4

You have a global x, and a local x variable in which you actually save the user input.
Using only the global variable will do the trick for you
#include <stdio.h>
int x;
void addSix(void)
{
int result = x+6;
printf("Result: %d\n", result);
}
int main()
{
printf("Please enter a number to add to 6: ");
scanf("%d", &x);
getchar();
addSix();
return 0;
}