#include <stdarg.h>
    #include <stdio.h>
 
    #define average(...) ( \
      _average((int[]){__VA_ARGS__}, sizeof((int[]){__VA_ARGS__}) / sizeof(int)) )
 
    double _average( int nums[], size_t size)
    {
        if (!size) return 0.0;
        double sum = 0.0;
        int i = 0;
        while (i < size) sum += nums[i++];
        return sum / size;
    }
 
    int main(void) {
        printf( "average: %.2f\n", average( 10, 20, 30));
        return 0;
    }
 

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