stdarg.h

#include
#include

int IntAvr(int NumOfInts, ...){
va_list args;
int sum=0;
int arg;
int i;
va_start(args, NumOfInts);
for(i=0;i arg = va_arg(args, int);
sum += arg;
}
va_end(args);
return sum/NumOfInts;
}

int main(){
printf("%d\n", IntAvr(4, 10, 20, 30, 10));
return 0;
}

Result: 17