Coding for multiple modes in C? - c

Question

My assignment is to find all possible modes for a set of numbers (0 to 100).
We were told to do so using arrays and also to count the frequency that each number occurs.
I've coded for the mode, however, my program does not work is there are multiple modes (example: 1, 2, 7, 7, 9, 10, 7, 2, 2. In this stance, 2 and 7 are both the mode and my program needs to print both of them, but mine doesn't).
I think I might have to make another array set, but I'm not sure? Any advice would be appreciated.
Here is what I have:
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
int main() {
int x, i, c[101], mode;
printf("please enter test scores between 0 and 100\n");
i = 0;
mode = 0;
while (i <= 100) { //setting all values to 0
c[i] = 0;
i = i + 1;
}
scanf("%d", &x); // scanning in the test scores
while ((x >= 0) && (x <= 100)) { // counting how often each score appears
c[x] = c[x] + 1;
if (c[x] >= mode) {
mode = x;
}
scanf("%d", &x);
}
printf("THE MODE(S) ARE %d\n", mode);
i = 0;
while (i <= 100) { //printing all values so long as they've occurred at least once
if (c[i] > 0) {
printf("%d occurs %d times\n", i, c[i]);
}
i = i + 1;
}
}

Answer 1

You have to count the highest frequency of any number and if that frequency equals the frequency of any other number then that number will also be mode.
So the changes that you need to do are:
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
int main ()
{
int x, i, c[101], mode;
printf("please enter test scores between 0 and 100\n");
i = 0;
mode = 0;
while (i <= 100) //setting all values to 0
{
c[i] = 0;
++i;
}
scanf("%d", &x); // scanning in the test scores
while ((x >= 0) && (x <= 100)) // counting how often each score appears
{
c[x] = c[x] + 1;
if (c[x] >= mode)
{mode = c[x];}
scanf("%d", &x);
}
for(i=0;i<=100;i++){//printing all values having highest frequency
if (c[i]==mode)
{
printf("THE MODE(S) ARE %d\n", i);
}
i = 0;
while (i<=100) //printing all values so long as they've occurred at least once
{
if (c[i] > 0)
{
printf("%d occurs %d times\n", i, c[i]);
}
++i;
}
}

Answer 2

Instead of determining the mode in the main entry loop, you should determine the maximum count. Then you can print all values with this count of occurrences in a final loop.
You should also check the return values of scanf().
I would also advise to use an initializer for the array to avoid a loop and to use for loops that more clearly identify the initialization, test and increment of the loop index.
Here is a corrected version of your code:
#include <stdio.h>
int main() {
int x, i, c[101] = { 0 }, max_repeat;
printf("please enter test scores between 0 and 100\n");
max_repeat = 0;
// read the test scores and compute the maximum repeat count
while (scanf("%d", &x) == 1 && x >= 0 && x <= 100) {
c[x] += 1;
if (max_repeat < c[x]) {
max_repeat = c[x];
}
}
printf("The mode(s) are");
for (i = 0; i <= 100; i++) {
if (c[i] == max_repeat) {
printf(" %d", i);
}
}
printf("\n");
return 0;
}