how the understand this function?

[winecoding]

just starting to learn C++, and sort of confusing about the following section of code:

int *getCharCountArray(char *str)
{
   int *count = (int *)calloc(sizeof(int), NO_OF_CHARS);
   int i;
   for (i = 0; *(str+i);  i++)
      count[*(str+i)]++;
   return count;
}

In specific, do not quite understand how the following two work?

for (i = 0; *(str+i);  i++)

and

count[*(str+i)]++;

[phoenix911]

for (i = 0; *(str+i);  i++)

this is a for loop, which will start with

i = 0

, and iterate through until the condition

*(str+i)

is met, and the iteration will move by one at a time as shown by the

i++

note: as far as i can remember the * indicates that its a pointer, correct me if im wrong

[WaltP]

str is a pointer to a character array.
Assume char *str = "ABCDEFG"; The first character in the array, 'A', can be represented as *str -- contents of str *(str+0) -- contents of 0th element of str
Expanding this last one, *(str+3) -- contents of 3rd element of str: 'D'

Therefore, the for loop tests the character at (str+i) to see if the end of the string has been reached -- the ending \0 count[*(str+i)]++; uses the character at (str+i) as an index to increment a value in count
If i = 0, it increments count, or count[65]
If i = 4, it increments count, or count[69]

[jonsca]

I believe it's a shortcut way of saying str[i] !='\0' since once the pointer hits the end of the string it will be null and therefore that statement *(str+i) will be false.

[winecoding]

str is a pointer to a character array.
Assume char *str = "ABCDEFG"; The first character in the array, 'A', can be represented as *str -- contents of str *(str+0) -- contents of 0th element of str
Expanding this last one, *(str+3) -- contents of 3rd element of str: 'D'

Therefore, the for loop tests the character at (str+i) to see if the end of the string has been reached -- the ending \0 count[*(str+i)]++; uses the character at (str+i) as an index to increment a value in count
If i = 0, it increments count, or count[65]
If i = 4, it increments count, or count[69]

Thanks for the reply.
What still confused me is that:
In general, an array is indexed by 1, 2, 3,etc. And we can have sth like A[1], A[2],…
But here, the count array is indexed by A,B, C. Is that right?

[WaltP]

Thanks for the reply.
What still confused me is that:
In general, an array is indexed by 1, 2, 3,etc. And we can have sth like A[1], A[2],…
But here, the count array is indexed by A,B, C. Is that right?

Almost. It's indexed by 'A', 'B', 'C'. Small detail but very important.

[mrnutty]

*(A+0) == A[0];
*(A+1) == A[1];
*(A+2) == A[2];
//...
*(A+n) == A[n]