Add an element to C array only if element does not exist - c

Question

I am trying to learn how to code in C, and I am trying to add unique characters to an array, from an input array, only if the character does not already exist in the unique array, in a very simple way.
I am really stumped and would appreciate some assistance how to think it through correctly.
Here's my code:
/* get each character and how many times it shows up
* to do this we need to store each unique char in a char array, and the count for each
* unique char in an int array */
char unique_chars[count];
for(int each = 0; each < count; ++each)
unique_chars[each] = '0';
/* count is the total number of chars stored in theinput array. */
int no_times = 0;
for(int each = 0; each < count; ++each)
{
if(theinput[each] != unique_chars[each])
unique_chars[each] = theinput[each];
if(theinput[each] == unique_chars[each])
continue;
for(int item = 0; item < count; ++item){
if(theinput[each] == unique_chars[item]){
++no_times;
}
}
printf("%c is in theinput array %d times.\n", theinput[each], no_times);
no_times = 0;
}
/* print all the values in the unique_chars array*/
printf("values in unique_chars are: \n");
for(int each = 0; each < count; ++each);
printf("\n");
return 0;
This is one of the many things I have tried. It returns the following:
./uniquely
exsss
The characters typed in are: exsss
Number of characters are: 6
values in unique_chars are:
e x s s s
Please how can I do this right?

Answer 1

You should rework the algorithm of your program as follows:
set count_unique to zero
for each index in the input
set count to zero
go through input to again using index i
if input[index] is the same as input[i]
count++
if count is 1 after the loop
unique_chars[count_unique++] = input[index]
for each index from zero to count_unique
print unique_chars[index]
However, this is the long way of doing it. The short way is to walk through the input once, increment counts, then walk through the counts, and print indexes of values of 1:
int counts[256];
for (int i = 0 ; i != count ; i++) {
counts[(unsigned)input[i]]++;
}
for (int i = 0 ; i != 256 ; i++) {
if (counts[i] == 1) {
printf("%c ", i);
}
}
printf("\n");