If statements not working with char array elements in C

I have to write this program where when the user enters a word, it changes it to the plural version of it. I have three rules.

1.) if it ends in a ‘y’, we change it to ‘ies’ 2.) if it ends in “sh” or “ch”, we add “es” to the end 3.) Else, We add a ‘s’ at the end

I have this function named WhichRule( char word[], char plural []), I am supposed to write if statements so I can see which rule to apply, the function WhichRule will call RuleOne( char word[], char plural []), RuleTwo( char word[], char plural []), and RuleThree( char word[], char plural []).

I am having trouble writing my if statements, the code im going to copy is two different ways in which I’ve tried to write my if statements, but none have worked. I would appreciate any help.

void WhichRule(char word[], char plural[])
{
    int len = strlen(word);


    if (word[len - 1] = 'y')
   {
        ApplyRuleOne(plural, word);
        printf("this");
    }

    else if (word[len - 2, len - 1] = 'c', 'h')
    {
        ApplyRuleTwo(plural, word);
        printf("is");
    }

    else if (word[len - 2] == 's' && word[len - 1] == 'h')
    {
        ApplyRuleTwo(plural, word);
        printf("a");
     }

    else
    {
       ApplyRuleThree(plural, word);
       printf("test");
    }
}