please explain the concept behind this problem

[Praveen30]

When i am running this code, nothing is printed on my terminal.i am using gcc compiler.can anyone explain me the concept behind it??i know this is related to signed and unsigned but i am not able to figure out..




#include<stdio.h>
#define TOTAL_ELEMENTS (sizeof(array) / sizeof(array[0]))
int array[] = {23,34,12,17,204,99,16};
int main()
{
int d;
for(d=-1;d <= (TOTAL_ELEMENTS-2);d++)
printf("%d\n",array[d+1]);
return 0;
}

[OlyPerson]

Have you tried any debugging? For example, you could print out the value of TOTAL_ELEMENTS before the loop to make sure it's the value you want (although it should be, don't see anything wrong there). Also, turn on -Wall in the compiler.

Also on a different note, you shouldn't use a for-loop in that way. By that I mean you should probably just start d=0 and go until TOTAL_ELEMENTS - 1 instead of 2 as that's the 'usual' way and is less confusing.


#include<stdio.h>
#define TOTAL_ELEMENTS (sizeof(array) / sizeof(array[0]))
int array[] = {23,34,12,17,204,99,16};
int main()
{
int d;
for( d = 0; d <= (TOTAL_ELEMENTS-1); d++ )
printf("%d\n",array[d]);
return 0;
}

See how that's easier to read?

EDIT: Did you actually want an explanation of what the code is doing or why it's not working?

Code works for me when I do the changes I posted.

[Senesence]

@OlyPerson

Additional information won't hurt him. ;)

@Praveen30

A relatively simple google search brought me to these useful links:

http://stackoverflow.com/questions/950051/confused-about-c-macro-expansion-and-integer-arithmetic

http://objectmix.com/c/208484-comparison-between-signed-unsigned-int.html

I think that should clear up your confusion.

[Bachstelze]

Te result of sizeof is unsigned, so when you compare d and TOTAL_ELEMENTS-2, the value of d is not -1 but 4294967295 (2^32-1).

[Praveen30]

@OlyPerson

Additional information won't hurt him. ;)

@Praveen30

A relatively simple google search brought me to these useful links:

http://stackoverflow.com/questions/950051/confused-about-c-macro-expansion-and-integer-arithmetic

http://objectmix.com/c/208484-comparison-between-signed-unsigned-int.html

I think that should clear up your confusion.

thanks for info, that's what i want!!!

[OlyPerson]

@OlyPerson

Additional information won't hurt him. ;)

@Praveen30

A relatively simple google search brought me to these useful links:

http://stackoverflow.com/questions/950051/confused-about-c-macro-expansion-and-integer-arithmetic

http://objectmix.com/c/208484-comparison-between-signed-unsigned-int.html

I think that should clear up your confusion.

Learn something new every day! Still young, hope I can keep that up my whole life.

[Arndt]

thanks for info, that's what i want!!!

You may want to ask gcc for warnings about this:


$ gcc -Wall -Wextra -c sign.c
sign.c: In function ‘main’:
sign.c:7: warning: comparison between signed and unsigned integer expressions