This question is very tricky actually. Our teacher wants us to write a program (in C) that gets an unknown amount of numbers from the user (until the user enters -1) and that counts the amount of numbers above the average WHILE INPUTING THE NUMBERS. The thing that makes this task hard is the fact that we are NOT allowed to use arrays. I tried to calculate the rate of change in the averages and come up with a conclusion about our guess regarding the amount of numbers that are no longer above the average when the user enters a certain "big" number, but nothing came up to my mind. I just don't know how this thing can be programmed without actually saving the numbers somewhere and checking them after the final number has been inputed. I don't even know if it's possible. Do you have any suggestions?
CodePudding user response：
This is impossible without keeping an amount of information proportional to the number of inputs, thus essentially requiring arrays.
Proof: Consider any sequence of n−1 inputs followed by a final input x. For illustration, suppose the set of allowed inputs is the rational numbers. By selecting x, we can make the average any rational number. (If the sum of the first n−1 inputs is s and we want the average to be a, then we select x = an−s.) So, we can select an x that is very slightly below 1 and that is very slightly above 1, and therefore the program must “know” whether 1 is in the prior inputs so that it can be included in the count. Similarly, we can select an x that is very slightly below or above any other number, and the program must respond accordingly. So the only way for the program to be able to produce a correct count for all possible inputs is if it has a record of all prior inputs.
CodePudding user response：
I believe that teacher is trying to teach you how to use malloc family functions.
I would do it this way:
typedef struct
{
size_t size;
int data[];
}data_type;
size_t countAbove(const data_type *data, int val)
{
size_t count = 0;
for(size_t i = 0; i < data -> size; i ) count = data -> data[i] > val;
return count;
}
int getAverage(const data_type *data)
{
long long sum = 0;
for(size_t i = 0; i < data -> size; i ) sum = data -> data[i];
return sum / data -> size;
}
data_type *addData(data_type *data, int val)
{
size_t newsize = data ? data -> size 1 : 1;
data = realloc(data, sizeof(*data) newsize * sizeof(data -> data[0]));
if(data)
{
data -> data[newsize - 1] = val;
data -> size = newsize;
}
return data;
}
int main(void)
{
data_type *data = NULL, *tmp;
int val = 0;
while(1)
{
printf("Enter number: ");
while(scanf("%d", &val) != 1);
if(val == -1) break;
printf("\n");
tmp = addData(data, val);
if(tmp) data = tmp;
else { /* add some error handling*/}
printf("Numbers above average %zu\n", countAbove(data, getAverage(data)));
}
free(data);
}