Question

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char * odd(const char * S, char * dest);

int main()
{
    char * source = "abcdefghijklmnopacegiacegi";
    unsigned int length = strlen(source);
    char dest[length];
    printf("%s\n",odd(source, dest));
}

char * odd(const char * source, char * dest)
{
    int count = 0;
    unsigned int length = strlen(source);
    for(int i = 0; i < length; i++)
    {
        if( (source[i] %2 )!= 0)
        {
            dest[count] = source[i];
            count++;
        }
    }
    return dest;
}

the size of dest increases and produces garbage for any values after the length of source

Answer 1

You have to manually include the ending \0 to the string, that is, at the end of add, you have to add:

dest[count] = '\0';

You know, the length of strings in C is accounted searching for the \0 character. You have to include one of those at the end of each C string. If not, the string may contain any garbage till the first \0 that will be printed.

Finally, when creating dest, you have also to increase the length of the reserved space in one to accomodate that ending 0 character. The strlen does not count that ending 0 character.