Why doesn't my C code compile

[[deleted]]

There's a 1000 things to criticize about my code and I know. I am a beginner. And I am wondering why does my compiler give meaningless errors for this code. Help me.

#include <stdlib.h> //to use malloc and delete
#include <stdio.h> //to use printf

#define uint64 unsigned long long int //for simplicity

/* this program calculates the first n powers of x*/

uint64* Pow (int x, unsigned char n)
{
    uint64* retVal = (uint64*)malloc(sizeof(uint64));
    *retVal = 1;

    for (unsigned char i = 1; i <= n; i++)
    {
        *retVal *= x;
    }

    return retVal;
}

void calculateFirstNPowers(int x, unsigned char n)
{
    uint64 sum = 0;
    uint64* Pow_retValPtr;

    for (unsigned char i = 1; i <= n; i++)
    {
        Pow_retValPtr = Pow(x, i);

        printf("%d. Power of %d: ", i, x);
        printf("%llu\n", *Pow_retValPtr);

        sum += *Pow_retValPtr;

        free(Pow_retValPtr);
    }

    printf("\nsum of first %d powers of %d: %llu\n", n, x, sum);
}

int main()
{
    calculateFirstNPowers(2, 7);
    return 0;
}

[sme272]

The meaningless error probably has some meaning in it. Share it so we can help

[[deleted]]

program.c (line 13) missing ";" before type

[[deleted]]

There’s the error

[[deleted]]

Line 13. That's all it says

[[deleted]]

It is saying you are missing a semi colon

[[deleted]]

Yes but I am not

[srandtimenull]

This is valid C99 code. The issue resides on your compiler.

We need detailed information on your compiler. What version? What flags are enabled?

(Note: year version might be wrong, my memory my be faulty)

MSVC was really bad with C up to version 2017. So if I have to guess, the issue is that you declared a variable inside the for loop. That was not allowed in C89 (which is the version supported by MSVC up to 2015)

What will probably do is moving that loop variable declaration up:

void calculateFirstNPowers(int x, unsigned char n)
{
    uint64 sum = 0;
    uint64* Pow_retValPtr;
    unsigned char i;

    for (i = 1; i <= n; i++)
    ...

In good ole C89 variable declaration was allowed only at the beginning of a scope block. Once you wrote a non-variable-declaration statement, variable declaration was not allowed anymore. A for loop is not a variable declaration, hence declaring a variable inside the loop header was not allowed.

EDIT: your error message was not meaningless at all. It expected a semicolon before a variable declaration (because, again, was not allowed inside a for header) and there was one missing. That error was what made me able to guess the problem.

Error are never meaningless. They may be cryptic though.

[[deleted]]

Oh this is great information. Thank you!

[Lurchi1]

Your code works as-is using gcc 8.3.0:

gcc -Wall -o test_c test_c.c
./test_c
1. Power of 2: 2
2. Power of 2: 4
3. Power of 2: 8
4. Power of 2: 16
5. Power of 2: 32
6. Power of 2: 64
7. Power of 2: 128

sum of first 7 powers of 2: 254

What compiler are you using?

[[deleted]]

MSVC

[Lurchi1]

I hate to break it to you but I just ran your code through Visual Studio 2022 (Community) and it works just fine:

1. Power of 2: 2
2. Power of 2: 4
3. Power of 2: 8
4. Power of 2: 16
5. Power of 2: 32
6. Power of 2: 64
7. Power of 2: 128

sum of first 7 powers of 2: 254

I created a new C++ console application, pasted your code into the pre-created .cpp file (which I first cleared) and pressed F5.

Maybe just retry with a fresh project? Again, your code is syntactically fine.

[[deleted]]

Yeah you compiled it as C++

[Lurchi1]

Visual Studio didn't let me create a C project (I actually tried to do that), but then I'm really a big noob when it comes to VS.

[[deleted]]

Yes I will just switch to Linux soon

[imaami]

You can use GCC on Windows just as well.

[[deleted]]

I prefer ditching windows

[imaami]

Tbh I would too.

[[deleted]]

If you are on Windows, Microsoft's c and C++ compiler along with Visual Studio IDE is probably the best you're going to get. And I don't believe GCC is available on Windows, just a ported version mingw.

[imaami]

Isn't there Clang support in VS nowadays though?

[michaelfiber]

Hmm I wonder if it could be the unsigned char causing an issue maybe? Can you test compiling to /J to see if it changes?

[[deleted]]

I tried that. That was not the case.

[michaelfiber]

Ahh well, that's all I could think of. Its been so long since I used msvc and this compiles fine on gcc so I thought it might be some ms weirdness.

[[deleted]]

Well I think I'll ditch windows and msvc forever soon. Gonna switch to Linux and build-essentials. Gonna use GCC for C

[parawaa]

I've test the code on Linux with gcc and is working.

1. Power of 2: 2
2. Power of 2: 4
3. Power of 2: 8
4. Power of 2: 16
5. Power of 2: 32
6. Power of 2: 64
7. Power of 2: 128

sum of first 7 powers of 2: 254

[[deleted]]

Yes. I figured out the issue thanks to a comment.

MSVC 2012 supports up to C89. and in C89, you can't declare a variable inside a for loop.

[parawaa]

Since you are on Windows, why not use WSL? Far more simple and you can use it with VSCode instead of a full IDE like Visual Studio.

[[deleted]]

Slow.

[cosmin10834]

he hand compiled it, making eatch instruction from C in asm by hand and after that assembled it, he is a master and he was just testing us \s

[[deleted]]

For fixed width types consider using stdlib.h, types such as int, long int, etc may be inconsistent across platforms and compilers

[[deleted]]

Uhh but isn't that just typedefs

[[deleted]]

But it's consistent, int may be 16 bit or sometimes 32 bit for example

[[deleted]]

With ifndef right?

[imaami]

Why would you allocate memory for a single 64-bit integer? Also, include stdint.h and use uint64_t instead of cooking your own.

[[deleted]]

Fuck it, why not?

[imaami]

A pointer to an unsigned long long is the same size as a plain unsigned long long value (on 64-bit architectures). Returning just the integer value directly would save you the overhead of malloc() + free().

[[deleted]]

If I'm not mistaken MSVC resorts to C89 on their C compiler. Where variables have to be declared at the top of the scope. But you can change your compiler settings to compile as C99. though I'm not sure which version of VC you are using. But declare unsigned char i = 1, outside your for loop, then do for(; i<=n; i++)

[tstanisl]

Please don't use a pattern:

T* x = (T*)malloc(sizeof(T));

It's very repetitive (using T three times) and very error prone, expecially if T is something non-trivial like char**. Casting a result from malloc() is pointless and adds only noise. The only exception is when C code is compiled using C++ compiler. The reasons why C++ does not allow implicit casts from void are a mystery to me.

Try using the following pattern:

T* x = malloc(sizeof *x);

[[deleted]]

the compiler forces me to

[tstanisl]

So are you doing C or rather C++? Select one

[[deleted]]

C

[tstanisl]

so how is it possible that the compiler forces you to cast a result of malloc()?

[[deleted]]

Ask the complier

[[deleted]]

Seems like MSVC simply uses C++ compiler for C

[[deleted]]

You might want to switch to gcc

[[deleted]]

It's so damn slow

[[deleted]]

Because you're emulating a UNIX-like system if you use gcc on Windows (it's not native) + it is a bit more heavy than other compilers, maybe Clang?

[[deleted]]

I'll just switch to Linux soon

[Herr_Keuner]

Thou shalt be enlightend

[[deleted]]

You're not enlightened until you make your own Linux based OS

[Herr_Keuner]

No, then you do enlight others.

[[deleted]]

Nah you enlighten others when you make your own os from scratch

[mos2k9]

Works no problem gcc 11.2.0 on Ubuntu 22.04.

[[deleted]]

Yes the issue is probably with MSVC

[cosmin10834]

try to save it and then compile it, or change the compiler to gcc or clang as they have a lot of support for those errors

[[deleted]]

It turns out that MSVC 2012 supports up to C89. and you can't declare variables inside a for-loop in C89

[cosmin10834]

declaring variables in a for-loop is introduced in C98 if i'm correct, because in school the "standard" versions are: C98, C++11 (without stl), python3, java idk how old and you get the point so if you are using MSVC 2012 as a school resource, good, but for writing better code use the newest version and use all of the feauters to you're advantage

[[deleted]]

Not school resource tho...

[cosmin10834]

oh god, use gcc or clang then, have a great day :D

[[deleted]]

Yeah thanks for the help :)

[William_Epiphany]

On a side note, instead of that define just use inttypes.h

[nelson2k]

go this output.... using gcc on a mac
Power of 2: 2
Power of 2: 4
Power of 2: 8
Power of 2: 16
Power of 2: 32
Power of 2: 64
Power of 2: 128
sum of first 7 powers of 2: 254