Error incomplete type is not allowed, simple array C

Question

I am building a program that should find a char in a string according to lower case alphabet.

#include <stdio.h>
#include <string.h>

int main()
{
    char str[];
    int i;

    for (i = 0; i < strlen(str); i++)
    {
                if (str[i] < 48 || str[i] > 57)
                break;
    }
    return 0;

}

I've never had this problem before and I used incomplete types (arrays and strings) hundered situations.
Anyway, Visual Studio 2012 alerts about incomplete type:

1   IntelliSense: incomplete type is not allowed    Visual Studio 2012\Projects\C\C\main.c  6   7   C

What is wrong?

"I used incomplete types (arrays and strings) hundered situations" -- Not likely. Note that char str[] as a parameter is not an incomplete type; it is equivalent to char* str in that context. (If you were to replace char str[] with char* str above, that would be undefined behavior and the program would probably crash.) And char str[] = "abc"; is also not an incomplete type -- the array size (4) is determined from the initializer. — Jim Balter
– Jim Balter, Commented Apr 10, 2014 at 23:18
if (str[i] < 48 || str[i] > 57) this sort of thing is useful for entries in "Obfuscated C" contests but is awful practice otherwise. — Jim Balter
– Jim Balter, Commented Apr 10, 2014 at 23:21

haccks · Accepted Answer · 2014-04-10 22:42:25Z

7

You must specify array size when you declare an array without initializer.

char str[SIZE];  
           ^Size of your array.

answered Apr 10, 2014 at 22:42

haccks

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