C: Undeclared identifier error - Pset2 (Caesar)

Question

I'm getting undeclared identifier errors for the letter i in the first 3 lines of code below.(Note: I have only posted the second part of the code). My algo is possibly a bit messed up too so far but I am only getting errors for these three lines. Some advice as to a succinct way to declare the 'i's would be good. Is it possible to modify just these lines?

    char original = word[i];
    int num[i];
    char cipher[i];

    if (isalpha (original))  //verify original input not integers
        {
        printf("ciphertext: ");
        num = atoi(argv[1]);  //change original string to integers

        for(int i=0; i<strlen(num[i]); i++) 
            {     

            if(isupper(original))  //if original characters are uppercase 
                {
                cipher[i] = (word[i]) - num -65)) % 26 + 65; 
                printf("%c", cipher[i]);
                }

                else (islower(original)) //for lowercase characters
                    {
                    char cipher[i] = (original) + num - 97)) % 26 + 97;
                    printf("%c", cipher[i]);
                    }

                //other remaining characters
            else
                printf(("%c", (original));  // or print them together
            } 

(Incidentally the code is supposed to convert code to numerical then apply a key then print as uppercase characters - confusing.)

Answer 1

Where is i declared before it is used in the first three lines? Based on the usage, I would guess that it should be declared as int i; somewhere before it is used, and initialized to some value.

If this isn't the problem, please edit the question and add the code that precedes the first 3 lines shown.

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