SImple C program with array is not printing proper output

Question

I wrote this incredibly stupid code

#include <stdio.h>
main(){
    int new[10], i;
    for(i=1; i<=10; ++i){
            new[i] = 0;
            }

for(i=1;i<=10; ++i)
            {
                    printf("%d", new[i]);
            }
 }

I compiled this using GCC on Xubuntu and then did the ./a.out. The cursor is just blinking resulting in no output. The same is the case when tried to debug with gdb. It runs and then stays with the blinking cursor.

Any help?

new is not a keyword in c, but in this era it is probably better to avoid using it as a identifier in new (heh!) code, simply because so many c programmers also write c++ and so much c code gets included into c++ projects. — dmckee --- ex-moderator kitten
– dmckee --- ex-moderator kitten, Commented Jul 23, 2013 at 17:05

Carl Norum · Accepted Answer · 2013-07-23 17:01:53Z

9

C arrays are 0 indexed - your program writes outside the boundaries of the new array, so it causes undefined behaviour. In this case, you probably are overwriting the i variable, so you end up with an infinite loop. You need to change your loops:

for (i = 0; i < 10; i++)
{
    new[i] = 0;
}

and:

for (i = 0; i < 10; i++)
{
    printf("%d", i);
}

answered Jul 23, 2013 at 17:01

Carl Norum

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5 Comments

Torsten Hĕrculĕ Cärlemän Over a year ago

Hi! It worked! Could you tell me why I didn't encounter the error in MinGW?

Carl Norum Over a year ago

Undefined behaviour is undefined. Anything could happen, including the possibility of correct-looking behaviour.

Torsten Hĕrculĕ Cärlemän Over a year ago

Thanks anyway! I went paranoid when it didn't print anything.

dmckee --- ex-moderator kitten Over a year ago

@AnuragPallaprolu The c compiler never promises to detect programer intent. You are assumed to know what you are doing and to say what you mean; if you ask for something strange (or even stupid) the compiler will generally give it to you.

Torsten Hĕrculĕ Cärlemän Over a year ago

@dmckee I assume it is very generous :)

lcta0717 · Accepted Answer · 2013-07-23 17:02:07Z

1

you need to have a new line character to see the output , or flush the stdout otherwise sometimes it doesn't print, or it will be combined with the next line... try:

printf("%d\n", new[i]);

also, set your for loop from 0 to 9

answered Jul 23, 2013 at 17:02

lcta0717

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Comments

rashok · Accepted Answer · 2013-07-23 17:12:52Z

1

int new[10] - Here new array can store 10 elements of type integer. You can access these elements from 0th to 9th index of array. Accessing beyond 9th index is undefined behavior.

edited Jul 23, 2013 at 17:12

answered Jul 23, 2013 at 17:06

rashok

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