A program to remove common alphabets from character array - c

Question

void main()
{
int i, j, k,flag=1;
char key[10], keyword[10];
gets(key);
i=0;
j=0;
while(key[i]!='\0') {
k=0;
while(keyword[k]!='\0') {
if(key[i]==keyword[k]) {
i++;
flag=0;
break;
}
k++;
}
if(flag==1) {
keyword[j]=key[i];
j++;
i++;
}
flag=1;
}
}
Here I tried to copy unique alphabets from array to another array ..means duplicate alphabet should not copied in another array..it shows right output but along with that it shows some garbage values like smiley or something till the length of original input array(i.e.key[])

Answer 1

You need to add a terminator to the unique character string both at the time it is initialized, and every time a new letter is added:
#include <stdio.h>
int main() {
int i = 0, j = 0;
char redundant[10], unique[10] = { '\0' };
gets(redundant);
while (redundant[i] != '\0') {
int k = 0, flag = 1;
while (unique[k] != '\0') {
if (redundant[i] == unique[k]) {
flag = 0;
break;
}
k++;
}
if (flag) {
unique[j++] = redundant[i];
unique[j] = '\0';
}
i++;
}
printf("%s -> %s\n", redundant, unique);
return(0);
}
OUTPUT
% ./a.out
warning: this program uses gets(), which is unsafe.
aardvark
aardvark -> ardvk
%
Now let's consider a different approach that wastes some space to simplify and speed up the code:
#include <stdio.h>
#include <string.h>
int main() {
unsigned char seen[1 << (sizeof(char) * 8)] = { 0 }; // a flag for every ASCII character
char redundant[32], unique[32];
(void) fgets(redundant, sizeof(redundant), stdin); // gets() is unsafe
redundant[strlen(redundant) - 1] = '\0'; // toss trailing newline due to fgets()
int k = 0; // unique character counter
for (int i = 0; redundant[i] != '\0'; i++) {
if (!seen[(size_t) redundant[i]]) {
unique[k++] = redundant[i];
seen[(size_t) redundant[i]] = 1; // mark this character as seen
}
}
unique[k] = '\0'; // terminate the new unique string properly
printf("%s -> %s\n", redundant, unique);
return 0;
}
Instead of a second, inner loop to search if a letter has been copied already, we use an array of flags (boolean), where the letter is the index, to determine if the letter has been processed.
Another thing you might want to think about is whether to treat upper and lower case differently or fold them into one.