Weirdest error message i've ever seen

/tmp/cckrJitj.o(.text+0x119): In function `main':
: undefined reference to `pow'
collect2: ld returned 1 exit status

here is my code (it's ugly, and i know a lot of unnecessary steps due to debugging i've tried):

Code:

#include <stdio.h>
#include <math.h>

int main()
{

        int sevens = 0;
        int input = 0;
        int digits;
        int division = 10000000;
        int counter = 8;
        int x = 7;
        int go = 1;
        float power = 0;
        int mod = 1;
        int counter2 = 0;
        int y;
        int powerint = 0;

        printf("Welcome to the amazing 7 finder machine. Give me any number ");
        printf("and I can tell how many 7s are in it(Whole numbers only): ");
        scanf("%d", &input);

        while (go == 1)
        {
                if (input / division >= 1)
                {
                        digits = counter;
                        go = 0;
                }
                division /= 10;
                counter--;
        }

        for (counter = 1; counter <= digits; counter++)
        {
                y = digits - counter;
                power = pow(10, y);
                x = (input / power);
                if (x == 7)
                {
                        sevens++;
                }
                for (counter2 = digits; counter2 >= counter; counter2--)
                {
                        mod *= 10;
                }

                input = (input % mod);
                mod = 1;
        }
        printf("\nThere are %d sevens in your integer. Thanks!\n", sevens);
        return 0;
}

please help, my deadline is tonight at midnight!!!

You're missing a header file.

[edit] no -- robwhit is right, you need to add -lm

gcc file.c -Wall -Werror -ansi -pedantic -lm

pow is in the math library.

ld is the linker. So since it got past the compiler, you know it's not a header file, probably. undefined reference means it can't find something that was referred to. In this case, it can't find the pow() function you were talking about. It automatically links with libc, but not libm, the math library. So it compiles, and then links with libc and your object file that it produced from your source file. Then it tries to resolve all the functions that are referred to in your object file. It can't find pow, so it stops and gives an error.

i have the math.h header file. so what other header do i need. if i change the code slightly, by removing the nested for loop involving counter2, then i just get the error that i have an invalid operand for binary %, which makes sense, since power is a float, and % only can use integers. So that's y i tried to make an integer the same size. but now it gives me the pow error again. should i make the loop earlier and forgo the pow function completely?

did i just answer my own question?

no, shikaku13, no!

just compile with -lm

oh. i didn't know what that meant. sorry. thank you. it's an assignment though, will my teacher think to do that?

edit: it works now, but it doent read a 7 in the last digit, can anyone help me with that?

Hopefully your instuctor will figure it out after every single assignment fails to link.

If you're in doubt, you can submit a makefile for him to use, but most likely he'll know what he is doing. You're fine.

Originally Posted by shikaku13

oh. i didn't know what that meant. sorry. thank you. it's an assignment though, will my teacher think to do that?

edit: it works now, but it doent read a 7 in the last digit, can anyone help me with that?

Your mod just didn't scale high enough.

Code:

for (counter2 = digits; counter2 > counter; counter2--)

makes it work.

power and mod are pretty much the same throughout. So you might want to optimize things.