Noticing a pattern of missing prototype warnings

Hi everyone. I've just begun picking up C today (with the ultimate goal of using the SDL library). As I'm moving along here, I'm beginning to notice some "missing prototype" warnings, for functions that should normally be working fine. First, the code:

Code:

---

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

/*char *lower(char upper[]) {
        char[sizeof(upper)] duplicate;
        for(i=0;i<sizeof(upper),i++) {
                duplicate[i] = tolower(upper[i]);
        }
}*/

int execFunction(char *func) {
        printf("Executing function \"%s\"...\n", func);
        char *lower = strlwr(func);
        if(func == "help") {
                system("cls");
                printf("--+HELP+--\n\n");
                printf("... Basically, there is no help.\nThe only function offered right now is this one.\n");
                printf("Thanks :)");
                getchar();
                system("cls");
        }
        else {
                printf("Sorry, that's not a function.");
                getchar();
                return -1;
        }
        return 0;
}

/* entry point */
int main(void)
{
        char input[127];
        int running = 0;
        printf("This is teh program! Type help for commands n' stuff.");
        gets_s(input, 127);
        execFunction(input);
        while(running == 0)
        {
                gets_s(input, 127);
                running = execFunction(input);
        }
    return 0;
}

---

And the errors:

Quote:

---

warning #2027: Missing prototype for 'strlwr'.
error #2168: Operands of '=' have incompatible types 'char *' and 'int'.
warning #2027: Missing prototype for 'system'.
warning #2027: Missing prototype for 'gets_s'.

---

(Don't worry about that error, I'll worry about it later.)

Anyhow, as you can see, it seems some of the most basic functions are being taken as missing prototypes. What am I doing wrong here?

Thanks in advance.

~TGP1994

Well you're better off using the standard fgets() rather than the non-portable gets_s

And system is in stdlib.h

As for the other one, I've no idea - it could be anything, anywhere (it isn't standard)

You don't have anything called "strlwr". You have something called "lower".
Since you don't have anything prototyped for "strlwr", it assumes it returns an int.
You don't have "system" prototyped, or rather, you haven't included stdlib.h.

Edit: Curses, foiled again!


Quzah.

Excellent, thank you guys. In case anyone is curious, here is my fixed code:

Code:

---

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

char lower(char upper[]) {
        char duplicate[sizeof(upper)];
        int i = 0;
        for(i=0;i<sizeof(upper);i++) {
                duplicate[i] = tolower(upper[i]);
        }
        return * duplicate;
}

int execFunction(char *func) {
        printf("Executing function \"%s\"...\n", func);
        char lwr = lower(func);
        if(func == "help") {
                system("cls");
                printf("--+HELP+--\n\n");
                printf("... Basically, there is no help.\nThe only function offered right now is this one.\n");
                printf("Thanks :)");
                getchar();
                system("cls");
        }
        else {
                printf("Sorry, that's not a function.");
                getchar();
                return -1;
        }
        return 0;
}

/* entry point */
int main(void)
{
        char input[127];
        int running = 0;
        printf("This is teh program! Type help for commands n' stuff.");
        gets(input);
        execFunction(input);
        while(running == 0)
        {
                gets(input);
                running = execFunction(input);
        }
    return 0;
}

---

I'm not sure why you have "lower" returning anything, since you never use it. Also, you cannot compare strings with ==, you will need something like strcmp in string.h instead. Finally, you should avoid gets. There's a FAQ on it.


Quzah.

Quote:

---

Originally Posted by quzah

I'm not sure why you have "lower" returning anything, since you never use it.

---

Code:

---

int execFunction(char *func) {
        printf("Executing function \"%s\"...\n", func);
        char lwr = lower(func);

---

Alright, I'll check out the FAQ for gets.

Thanks!

The code is fundamentally broken. It's not fixed... yet.
>>char duplicate[sizeof(upper)];
Since upper is an argument, this is the size of a pointer. Always. Not what you want.
It should be strlen(input) + 1.

Also, as noted, you cannot compare strings with ==. You must use strcmp.
And gets is the devil's tool. Here's an explanation of why: SourceForge.net: Gets - cpwiki

And quzah is right. lwr is not used anywhere, so it's unnecessary.

Quote:

---

Originally Posted by Elysia

The code is fundamentally broken. It's not fixed... yet.
>>char duplicate[sizeof(upper)];
Since upper is an argument, this is the size of a pointer. Always. Not what you want.
It should be strlen(input) + 1.

Also, as noted, you cannot compare strings with ==. You must use strcmp.
And gets is the devil's tool. Here's an explanation of why: SourceForge.net: Gets - cpwiki

And quzah is right. lwr is not used anywhere, so it's unnecessary.

---

Ah, I see what he was talking about now for lwr not being used. Looks like I just forgot to use the correct variable later. And yup, I'm using fgets now.

Anyhow, it seems I'm not defining lwr correctly, since I'm receiving this; "Illegal initialization of variable-length array 'lwr'." (Originally, it was complaining about attempting to compare argument 1 in strcmp, expecting a const char *, but receiving a char, so I think I have to initialize lwr as an array.)

Here's what that block of code looks like:

Code:

---

int execFunction(char *func) {
        printf("Executing function \"%s\"...\n", func);
        char lwr[sizeof(func)] = lower(func);

---

Although it seems like sizeof() should be returning a datatype that's very close to int. (I'm reading up on an a topic about that as we speak.)

(Later)
Ah, so it's giving me the physical size of the pointer, rather than what it's pointing too? It seems like I can't use strlen in this case.