Passing an Array as an Argument - Vigenere

Question

I am making a function out of the encryption process (since I wrote two identical ones minus the subtraction value drawn from ASCII).

One of the arguments is an array which I declared in the function as int x[]. My code will not compile if I call the array keyword_num[], but it will if I just use keyword_num. The error I get is "expected expression", when I attempt to compile it with keyword_num[]. If I call keyword_num it compiles but doesn't encrypt correctly, as the commented out block below it does.

My question is if I am not passing an array as an argument correctly, how would I do so? Below is my code so far, with the array called as keyword_num[].

#include <cs50.h>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define UPPERMAX 90
#define LOWERMAX 122
#define NUMLETTERS 26

void vencrypt(int r, int x[], int y, int z, string q);

int main(int argc, string argv[])
{
// declares counter for keyword array
int keycount = 0;

// checks if correct number of arguments provided
if (argc == 2)
{
    // cycles through argument
    for (int i = 0, n = strlen(argv[1]); i < n; i++)
    {
        // checks if each character is a letter
        if (isalpha(argv[1][i]) == false)
        {
            // prompt reminding user only letters allowed in argument
            printf("Please submit a command line arguement containing only letters.\n");
            // returns error
            return 1;
        }
    }
}

// ensures there is one command line argument
else
{
    // prompt reminding user only one command line argument is allowed
    printf("Please only submit one command line argument.\n");
    // returns error
    return 1;
}

// stores argument as keyword
string keyword = argv[1];

// creates an array for the corresponding numeric values to be stored in
int keyword_num[strlen(argv[1])];

// converts keyword into an array of corresponding numbers
for (int i = 0, n = strlen(argv[1]); i < n; i++)
{
    if (isupper(keyword[i]))
        keyword_num[i] = (int) keyword[i] - 65;
    if (islower(keyword[i]))
        keyword_num[i] = (int) keyword[i] - 97;
}

// gets user input and stores it in plaintext
string plaintext = GetString();

// runs through length of plaintext
for (int i = 0, n = strlen(plaintext); i < n; i++)
{
    // resets spot in keyword array when maxed
    if (keycount == strlen(keyword))
        keycount = 0;

    // checks if character is letter
    if (isalpha(plaintext[i]))
    {
        // checks if letter is uppercase
        if (isupper(plaintext[i]))
        {
            vencrypt(i, keyword_num[], keycount, UPPERMAX, plaintext);
            // converts letter to ascii equivalent 
            // int upper_number = (int) plaintext[i];
            // adds shift value
            // int upper_encode = upper_number + keyword_num[keycount];
            // loops from z to a (in ascii numbers)
            // if (upper_encode > 90)
                // upper_encode = upper_encode - 26;
            // converts new number into letter    
            // char upper_letter = (char) upper_encode;
            // prints new letter
            // printf("%c", upper_letter);
            // increments spot in keyword array
            // keycount++;
        }

        else
        {
            vencrypt(i, keyword_num[], keycount, LOWERMAX, plaintext);
            // converts letter to ascii equivalent
            // int lower_number = (int) plaintext[i];
            // adds shift value
            // int lower_encode = lower_number + keyword_num[keycount];
            // loops from z to a (in ascii numbers)
            // if (lower_encode > 122)
                // lower_encode = lower_encode - 26;
            // converts new number into letter    
            // char lower_letter = (char) lower_encode;
            // prints new letter
            // printf("%c", lower_letter);
            // increments spot in keyword array
            // keycount++;
        }
    }
    else
    {
        // prints character untouched
        printf("%c", plaintext[i]);
    }
}

// prints new line
printf("\n");
// returns a value of zero
return 0;
}

void vencrypt(int r, int x[], int y, int z, string q)
{
// converts letter to ascii equivalent 
int number = (int) q[r];
// adds shift value
int encode = number + x[y];
// loops from z to a (in ascii numbers)
if (encode > z)
    encode = encode - NUMLETTERS;
// converts new number into letter    
char letter = (char) encode;
// prints new letter
printf("%c", letter);
// increments spot in keyword array
y++;
}

Answer 1

Here is an example of passing an array to a function:

#include <stdio.h>

void print_nums(int nums[], int length);

int main(void)
{
    int nums[] = { 1, 2, 3, 4, 5 }; // declare the array
    int length = sizeof(nums) / sizeof(nums[0]);    // get the size of the array

    print_nums(nums, length);
    return 0;
}

void print_nums(int nums[], int length)
{
    for (int i = 0; i < length; i++)
    {
        printf("%d\n", nums[i]);
    }
}