OK, so let me do this as two parts -- great question! First, I'm assuming you mean (e.g.) for an input of 5, you want the average of 1, 2, 3, 4, 5. 1+2+3+4+5=15 / 5 = 3.
This is pretty straight forward to write:
int main() {
unsigned n, c;
double sum;
printf("What is the max number? ");
scanf("%d", &n);
for (c=1; c <= n; sum+=c++) ;
printf("average=%lf", sum / n);
return 0;
}
However, the real trick here is to realize you don't need to do a loop :) For the sequence 1,2,3,4,5
1+5 = 6 / 2 = 3
2+4 = 6 / 2 = 3
3 = 3 / 1 = 3
In other words, the average of a range of numbers from 1...N is (N+1) / 2. You can therefore re-write this as:
int main() {
unsigned n, c;
double sum;
printf("What is the max number? ");
scanf("%d", &n);
printf("average=%lf", ((double)(n+1)/2));
return 0;
}