Go4Expert - Add all elements of an array

Here's how:
Code:
#include <stdio.h>



int main (void)

        {

        int n, sum;

                printf("?: Specify a number of values.\n\ni: The x variables are by default started at 0 and your desired number should be the highest x variable. If any slots in the x array are not available, you should leave the frequency fields at 0.\n\nTherefore, your highest value of x please: ");



                scanf("%i", &n);

                printf("i: Success: Array size set to contain %i elements (including 0)\n\n", n);



        int size = n, values[size];



                for ( size = 0; size < n; ++size )

                {

                        printf("?: For x = %i, f = ?: ", size);

                        scanf("%i", &values[size]);

                        printf("i: Success: When x = %i, f = %i\n\n", size, values[size]);

                }



                printf("i: Now printing a table of data . . .\n\n");

                printf("|  x (Variable)     |  f (Frequency)    |\n");

                printf("-----------------------------------------\n");



                for ( size = 0; size < n; ++size )

                {

                        printf("|  %3i              |  %3i              |\n", size, values[size]);

                }



                printf("i: END\n");



        int values_copy = values, sum_up;



                /*add all values so as to find the mean*/



                for ( size = 0; sum_up = 1; sum_up < n; ++sum_up )

                {

                        sum = values_copy[size] + values_copy[sum_up];

                }

                printf("int sum = %i\n", sum);

        return 0;

}
But the last for loop is dead. Always complainin'. This program is meant to find the mean of a set of unnamed number of values.