Thread: what is the output

Code:

a[]={0,1,2,3,4};
a[i]=i;

but i is not declared so what it return why?


thank you..!!

If i is not declared the program won't compile so it won't return anything. If i is declared but not initialized then it is undefined what value i will contain.

Jim

ideone says

cc1: warnings being treated as errors
prog.c:1: error: data definition has no type or storage class
prog.c:1: error: type defaults to ‘int’ in declaration of ‘a’
prog.c:2: error: ‘i’ undeclared here (not in a function)
prog.c:2: error: data definition has no type or storage class
prog.c:2: error: type defaults to ‘int’ in declaration of ‘a’

You can see the output for yourself

Originally Posted by jimblumberg

If i is declared but not initialized then it is undefined what value i will contain.

Jim

In other words What is the default value of integer in c

Originally Posted by qny

ideone says
You can see the output for yourself

Well that's ok,because then the compiler says what's wrong...but if the code looks like this

Code:

int main(void)
{
   int i;
   int a[]={0,1,2,3,4};
   a[i]=i;
   return 0;
}

then the compiler will tell nothing,but i is uninitialized so actually we have a logic error here,which of course is more difficult to detect(in large programs) than the syntactic ones

then the compiler will tell nothing,but i is uninitialized

Actually my compiler tells me about using uninitialized variables.

main.c||In function ‘main’:|
main.c|4|warning: variable ‘a’ set but not used [-Wunused-but-set-variable]|
main.c|5|warning: ‘i’ is used uninitialized in this function [-Wuninitialized]|
||=== Build finished: 0 errors, 2 warnings ===|

Jim

Originally Posted by jimblumberg

Actually my compiler tells me about using uninitialized variables.
Jim

I suppose then it is up to the compilers and the versions of it.I compile it in a Linux with an old i would say compiler

If you are using Linux you are probably using gcc which is what I used. What compiler switches are you using? Are you at least using -Wall -Wextra?

Jim

Originally Posted by jimblumberg

If you are using Linux you are probably using gcc which is what I used. What compiler switches are you using? Are you at least using -Wall -Wextra?
Jim

No flags at all. gcc -o programName fileName.c .
I used what you did (h.c was the file i created and compiler said nothing again.) I am via putty(is this relevant ? )

Code:

linux11:/home/users/std10093>pico h.c
linux11:/home/users/std10093>gcc -o  -Wall -Wextra h h.c
gcc: h: No such file or directory
linux11:/home/users/std10093>gcc -Wall -Wextra -o h h.c
linux11:/home/users/std10093>h
Segmentation fault
linux11:/home/users/std10093>gcc -o h h.c
linux11:/home/users/std10093>h
Segmentation fault
linux11:/home/users/std10093>

Here is a complete list of the warning options I use:

-Wshadow"
-Winit-self"
-Wredundant-decls"
-Wcast-align"
-Wundef"
-Wfloat-equal"
-Winline"
-Wunreachable-code"
-Wmissing-declarations"
-Wmissing-include-dirs"
-Wswitch-enum"
-Wswitch-default"
-Wmain"
-pedantic-errors"
-pedantic"
-Wextra"
-Wall"
-g"
-std=c11"

You cant try add them one at a time, I recommend using at least the -Wall -Wextra -pedantic every time you compile.

Jim