first program in C in Ubuntu

tigertim71 · 02-28-2009, 05:34 PM

Hi-

I'm trying to get a first program going in C in Ubuntu 8.04.

It's the usual "hello world" stuff the books introduce you to but there's a few things I can't understand at this stage.

The book mentions a /home/MyPrograms directory. I can't seem to find this at all? And should my program be saved in a text document labeled (name).c
eg. hello.c?

From what I can see the final commands are executed in the terminal.

Could someone please explain...

Thanks

AceofSpades19 · 02-28-2009, 05:42 PM

You would want to make a directory called /home/MyPrograms. Yes, you should name your source code files with the .c extension.
To compile a helloworld.c file eg.

Code:

include <stdio.h>

int main(){
    printf("Hello World");
    return 0;
}

You would want to run this command to compile it:

Code:

gcc helloworld.c -o helloworld

That creates a program called helloworld
To run it, first make sure its executable by running

Code:

chmod +x helloworld

Then run

Code:

./helloworld

and that should output Hello World

amani · 02-28-2009, 05:46 PM

#mkdir ./MyPrograms

save your text file as hello.c there

#cd ./MyPrograms

read the apt-get manual as well

tigertim71 · 02-28-2009, 06:47 PM

I did a couple of things but no result.

The first was to manually create a MyPrograms directory in /home/myusername, put the home code in there in a home.c text file, but all I got was

Code:

gcc: hello.c: No such file or directory
gcc: no input files

after putting in the terminal instructions gcc hello.c -o hello.exe

I then tried the

Code:

#mkdir ./MyPrograms

(as below), after deleting my manual entry (as above) but could not find the directory.

Any suggestions?

AceofSpades19 · 02-28-2009, 07:34 PM

Quote:

Originally Posted by tigertim71

I did a couple of things but no result.

The first was to manually create a MyPrograms directory in /home/myusername, put the home code in there in a home.c text file, but all I got was

Code:

gcc: hello.c: No such file or directory
gcc: no input files

after putting in the terminal instructions gcc hello.c -o hello.exe

I then tried the

Code:

#mkdir ./MyPrograms

(as below), after deleting my manual entry (as above) but could not find the directory.

Any suggestions?

if you have a filename called home.c, you wouldn't compile it with
gcc hello.c -o hello, you would compile it with gcc home.c -o home and you do not need to put the .exe extension for a program

paulsm4 · 03-01-2009, 02:41 AM

Hi, Tigertim71 -

I wouldn't worry about the "/home/MyPrograms" stuff. Just focus on compiling your program:

Quote:

1. Create your "hello.c" text file:

Code:

#include <stdio.h>

int
main (int argc, char *argv[])
{
  printf ("hello world!\n");
  return 0;
}

2. Verify that the file exists (this is actually important):

Quote:

ls -l hello.c
<= If you don't see "hello.c" when you type this "ls -l" command, you're going to have problems. Post back if you have any problems up to this point

3. Compile and link the file ("gcc" does both things for you at once):

Quote:

gcc -g -Wall -o hello hello.c
<= These extra "flags" ("-g" and "-Wall") will help you debug more advanced programs you write

4. Execute:

Quote:

./hello

'Hope that helps .. PSM

PS:
Linux offers many IDE's (kdevelop and Eclipse, among many others) to simplify compiling and debugging programs, should you prefer.

tigertim71 · 03-01-2009, 04:02 AM

Hi paulsm4,

Thanks for your post. I'm stuck on stage 2 and am looking into other areas of investigation as to why this is going wrong.

I'm quite new to Ubuntu so am wondering if this could be another reason:

Originally, my system is set up as a dual boot with XP. Going into gparted everything looks fine. But looking in the Ubuntu system monitor I get this:

device directory type total free available used
/dev/sda3 / ext3 9.2 GB 6.4 GB 6.0 GB 2.8 GB
/dev/sda4 /home ext3 36.0 GB 35.8 GB 34.0 GB 216.2 MB
gvfs-fuse-daemon /home/mysystemname/.gvfs fuse.gvfs-fuse-daemon
9.2 GB 6.4 GB 6.0 GB 2.8 GB
/dev/sda1 windows fuseblk 55.9 GB 41.3 GB 41.3 GB 14.6 GB

Why is / exactly the same as /home/mysystemname.gvfs or is this just normal? Could this be causing a conflict with trying to locate the hello.c file?

paulsm4 · 03-01-2009, 11:49 AM

Q: How did you create "hello.c"
<= the way you edited this file might give some clues as to where we can find it

Quote:

EXAMPLE:
1. I log in to Ubuntu 8.04 (I happen to be using the Gnome desktop)

2. I bring up a command prompt:
Applications, Accessories, Terminal

Quote:

pwd
/home/paulsm
<= This tells me the directory my command prompt is in

3. I start a text editor:
Applications, Accessories, Text editor
a) I type in "hello world"
b) I "Save"
Name= hello.c
Save in Folder= paulsm
[Save]

4. Back in the command prompt, I type "ls -l", and I see "hello.c" (I see it because I'm in directory "/home/paulsm").

5. I look for "hello.c":
Applications, Places, Search for Files...
Name contains= hello.c
Look in folder= paulsm
[Find]

pwd

tigertim71 · 03-01-2009, 02:44 PM

Hi paulsm4,

OK- the good news is that I've passed stage 2 of your first post. I did notice however that the system seems to prefer it if files are kept in my own home directory and not in a new folder eg /MyPrograms.

I also noticed 2 hello files after entering "ls -l":

77 2009-03-01 19:00 hello.c
99 2009-03-01 18:43 hello.c~

but in search for files, there is only 1 so this may not be significant.

However, at stage 3, when I enter

Code:

gcc -g -Wall -o hello hello.c

I get the following message:

Code:

hello.c:1:19: error: stdio.h: No such file or directory
hello.c: In function ‘main’:
hello.c:6: warning: implicit declaration of function ‘printf’
hello.c:6: warning: incompatible implicit declaration of built-in function ‘printf’

but at least I'm passed stage 2.....

paulsm4 · 03-01-2009, 03:16 PM

Hi -

It sounds like you're nearly home free (and apologies that you've invested this much effort - things usually go a lot quicker and smoother. Honestly!)

ANYWAY:
1. From your command prompt, type:

Quote:

dpkg -l|grep -i gcc
ii gcc 4:4.2.3-1ubuntu6 The GNU C compiler
ii gcc-4.2 4.2.3-2ubuntu7 The GNU C compiler
ii gcc-4.2-base 4.2.3-2ubuntu7 The GNU Compiler Collection (base package)
ii libgcc1 1:4.2.3-2ubuntu7 GCC support library
ii libgomp1 4.2.3-2ubuntu7 GCC OpenMP (GOMP) support library
<= I'm guessing you *have* gcc (the compiler), but you need to install the C runtime headers and libraries

2. Use the Synaptic GUI to install:
Administration, Synaptic, Search, gcc
<= Install:
gcc-4.2 (or whatever your current version is)
gcc-4.2-base (this is probably what's causing the error)
gcc-4.2-doc (optional...but helpful)
libgccl (if you're missing the .h headers, you should also make sure you have all the C runtime libraries, too)
<= Install g++

3. If you did a "File, Save as" hello.c to "/home/MyPrograms", you should be able to compile it like this:

Quote:

gcc -o hello /home/MyPrograms/hello.c
... OR ...
cd /home/MyPrograms
gcc -o hello hello.c

There's nothing "magic" about /home/MyPrograms

4. The "hello.c~" is almost certainly either a temp file (created by your text editor), or a backup file (created by your text editor)

5. For more complicated programs, obviously, you won't be typing "gcc -o hello hello.c" on a command line. You'll probably instead use tools like "make" (for batch-oriented builds from a command line), or "kdevelop" (an interactive GUI for creating and debugging programs).

'Hope that helps .. PSM

tigertim71 · 03-01-2009, 06:01 PM

Hi paulsm4,

Many Thanks. I have faith now that the best motto is: don't give up.

I just saw "hello world!" on my screen...