question

[Dale Kingston]

ok i have a question on how to do something, i'm bad with words so i'll show
the code.

void encrypt(char *string)
{
    int i, c;
    char buf[MSL];

 for(i = 0; string[i] != '\0'; i++)
  {
   for (c = 0; key_table[c].letter1 != NULL; c++)
    {
             if (!str_cmp(string[i], key_table[c].letter1))
                string[i] = key_table[c].letter2;
    }

  }
 return;
}
and the struct is defined
struct key_type
{
    char *letter1;
    char *letter2;
};

How to i change string[i] to key_table[c].letter2?

I know this is probly a stupid question but i'm like brain dead ATM. thanks
in advance