Trying to use functions to modify pset2 Caesar characters, get error: expression result unused for each function

Question

So I'm working on pset2's Caesar and wanted decided it would be better to put the algorithm into functions, with each function operating based on whether a character is uppercase or lowercase. Now that I'm trying to integrate those functions into the main function, I get

error: expression result unused [-Werror,-Wunused-value]

For each function. Maybe I'm just making this more complicated than I need to, or maybe I'm going in a totally wrong direction, but these are the last two errors I have to clear. Here's my code:

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

void lowercase(char character);
void uppercase(char character);
int big_letters = 65;
int small_letters = 97;
//int key = argv[1];
int enciph_Len;
string encipher;
//void lowercase(int n);
int key;

int main(int argc, string argv[ ])
{

    if (argc != 2)
    {
        printf("ERROR: COMMAND LINE ARGUMENT NOT ENTERED. EXITING \n");
        return 1;
    }


    printf("Enter message you want enciphered:\n");
    encipher = get_string();
    enciph_Len = strlen(encipher);

    key = atoi(argv[1]);

    for (int i = 0; i < enciph_Len; i++){

        if (isalpha(encipher[i]) ){
            if(isupper(encipher[i])){
                uppercase(encipher[i]);
            } else if (islower(encipher[i])){
                lowercase(encipher[i]);
            }

            printf("%c", encipher[i]);
        } else {
            printf("%c",encipher[i]);
        }
    }printf("\n");


    printf("%i\n", key);



}

void uppercase(char character){
        (character+key) % 26 + big_letters;
}

void lowercase(char character){
        (character+key) % 26 + small_letters;

}

Then I get this after trying to make/compile the program:

~/workspace/pset2/caesar/ $ make caesar
clang -fsanitize=signed-integer-overflow -fsanitize=undefined -ggdb3 -O0 
-std=c11 -Wall -    Werror -Wextra -Wno-sign-compare -Wshadow    
caesar.c  -lcrypt -lcs50 -lm -o caesar
caesar.c:59:30: error: expression result unused [-Werror,-Wunused-value]
            (character+key) % 26 + big_letters;
            ~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~
caesar.c:63:30: error: expression result unused [-Werror,-Wunused-value]
         (character+key) % 26 + small_letters;
         ~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~

2 errors generated. make: *** [caesar] Error 1

Thanks for any help!

Answer 1

It's exactly what it says. You have written an expression:

(character+key) % 26 + big_letters;

but you aren't setting the results of that expression to anything, hence it is unused.

You're doing the equivalent of saying

3 + 6

I'm guessing you actually want that function to calculate a new value and return it to main? If that's the case, then it can't be a void function, but should return the value you are calculating.