Strange Issue with GCC

[jwesleycooper]

I'm currently trying to learn C/C++ on my own in a Linux environment, but I've came up against an issue whilst using GCC that just doesn't make any sense to me.

You see, I'm trying to compile an example program I found in an online tutorial, as shown below:

#include <math.h>

main()
{
  int i;
  printf("\t Number \t\t Square of Number\n\n");
  for(i = 0; i <= 360; ++i)
    printf("\t %d \t\t\t %d \n", i, sqrt((double) i));
}

But GCC gives me the following output when I try to compile:

jwesleycooper@linux-twom:~/C> gcc Exercise12172.c
Exercise12172.c: In function ‘main’:
Exercise12172.c:6:3: warning: incompatible implicit declaration of built-in function ‘printf’
/tmp/ccy7FQEn.o: In function `main':
Exercise12172.c:(.text+0x3f): undefined reference to `sqrt'
collect2: ld returned 1 exit status

Can anyone explain to me why this is happening, and how I might correct it?

Thanks!

EDIT: The tutorial on this site appears to be geared solely at Windows users (I've yet to find an iostream header for Linux), so is there anywhere I might find a proper *Linux* C/C++ tutorial?

[Bazzy]

You need to #include <stdio.h> and link to the math library

(I've yet to find an iostream header for Linux)

What?

[Athar]

That's because you're mixing up C and C++.
They're two different languages and there is no iostream header in C.
There certainly is no such language as "C/C++".

[jwesleycooper]

You need to #include <stdio.h> and link to the math library

Ok, but how do I link to the math library?

That's because you're mixing up C and C++.
They're two different languages and there is no iostream header in C.
There certainly is no such language as "C/C++".

I'm trying to learn both of them, sorry that I got mixed up. So I just need to make sure that the file extension is .cpp if I want to use C++ then?

[Bazzy]

Ok, but how do I link to the math library?

-lm

[jwesleycooper]

-lm

Could you please be just a *little* less cryptic Bazzy? I am quite new at this, you know.

[Bazzy]

pass it as argument to gcc

[jwesleycooper]

Ok, that worked now... so what exactly do the 'l' and 'm' flags do? The command gcc -v --help says it's this this:

-l LIBNAME, --library LIBNAME
                              Search for library LIBNAME

and this:

-m EMULATION                Set emulation

But that doesn't really help me understand what it's actually doing...

[jsmith]

-lm links the math library, libm.a. It is one command-line option, not two.

[bigearsbilly]

the easy way, with simple standalone files
is to use 'make' and implicit rules...

(note: remove extension on using make)

$ export LDLIBS=-lm
$ make Exercise12172
   cc     Exercise12172.c  -lm -o Exercise12172

much less typing, the programmer's skill of laziness

[jwesleycooper]

Thanks for your explanations and advice everyone, you've all been very helpful! :-)