Need to find Max, Min, Avg number in Array - no size declared

Question

So I have this array, I need to find the Min, Max, and Average. I have figured out how to get the Max, my code looks right for the minimum but it does not work so I must be missing something. I also need to find the average of the numbers entered. Everything I can find on this only works when you have the size of the array set. I have a max size set for the array but it does not get filled by user input. I have been staring and testing on this for days and still cant figure it out.

I know for the average I need something like (with added declartions at the top), but I cannot figure out how to get it to work:

for (i = 0; i < numOfGrades; i++) {
    sum += grades[i];
    }
avg = (double) sum / numOfGrades;

---

Here is the rest of my code:

#include <stdio.h>

int main(){

int grades [100]; 
int i = 0;
int small, big, input;

printf("Enter a series of grades. When done, enter any number above 100.\n\n");

while (i <= 100) { //while loop to set maximum for array
    printf("Enter grade:");

    if (scanf("%d", &input) == 1) {
        if (input >= 0 && input <=100) {  
            grades[i] = input; //if good, add to array
            i++;
            }
        else {
            printf("\n\nExiting entry.\n");
            printf("\n\nGrades entered:\n\n");
            i = i - 1;
            break; //exiting loop
            }
        }
    }
int x, y;
    for (x = 0; x <= i; x++) {
        printf("Grade: %d\n", grades[x]);  //print array
        }
    big = small = grades[0];
    for (y = 0; y < i; y++) {
        if (grades[y] > big) {
            big = grades[y];
            }
        else if (grades[y] < small) {
            small = grades[y];
            }
        }
    printf("Highest number : %d\n", big);
    printf("Smallest number: %d\n", small);

    return 0;
}

Answer 1

Here you do the right thing:

 for (x = 0; x <= i; x++) {

Because x <= i will take you from 0 to the value of i . Then in your min/max loop you do this:

 for (y = 0; y < i; y++) {

So you are going from 0 to to i-1 . You have 2 options:

1. Make the above loop correct with y <= i .
2. Dont decrement i in the while loop (Dont do this i = i - 1; ) That way, i represents the number of numbers entered, instead of number of numbers entered -1 (you will need to fix the x <= i to x < i ).

Here is a live example. http://ideone.com/ZEaDue

To calculate the average, you are doing the right thing, you can re-use i though:

int sum = 0, avg = 0;
for (y = 0; y < i; y++) {
    sum += grades[y];
}
avg = (double) sum / i;
printf("Avg: %d\n", avg);

Answer 2

Actually you do have the number of grades

   if (scanf("%d", &input) == 1) {
        if (input >= 0 && input <=100) {  
            grades[i] = input; //if good, add to array
            i++;
            }
        else {
            numOfGrades=i;
            printf("\n\nExiting entry.\n");
            printf("\n\nGrades entered:\n\n");
            i = i - 1;
            break; //exiting loop
            }

As for the minimum, your logic should be like this:

for (y = 0; y < numOfEdges; y++) {
    if (grades[y] > big) {
        big = grades[y];
        }
    if (grades[y] < small) {
        small = grades[y];
        }
    }

The else statement I removed should do the trick. Also I would always use

for(int var = 0; var < numOfEdges; var++) in any of the loop constructs. It's easyer to follow the logic this way: You have counted the number of edges (numOfEdges), but your loop goes only to numOfEdges-1 since you start with index 0.