C ints and chars. Strange behavior

Question

I am learning C language and I am facing a problem I don't seem to be able to resolve on my own. I have a simple loop where I add up ascii values of all characters in each word.

 char char_array[100]; int lexicographical_values[20]; int i, j = 0; for( i = 0; i <strlen(char_array); i++) { if(char_array[i] == ' ') j++; lexicographical_values[j] += (int)char_array[i]; }

Then, if I output the lexicographical_values array in a loop

 printf("%d word is: %d \n", i, lexicographical_values[i]);

I get correct figures for each word (ex: dd = 200 and so on)

But if I actually look at each element's value in the array, I get big numbers that are far from being correct.

The question is, how do I get correct values and how does printf obtain the correct values?

Thanks

The elements in which array is wrong? How are you looking at them? How are you getting the right answer if the numbers are wrong? Also, are you meant to be adding the value for space too? — freespace
– freespace, Commented Jan 12, 2010 at 2:29
The cast from char to int is unnecessary (just like you didn't use one when comparing to ' ', which is an int constant). — caf
– caf, Commented Jan 12, 2010 at 2:38
You don't need the cast to (int) since char type is integral and there will be implicit conversion, but apart from using uninitialized memory, the biggest problem is your assumption that a char's value represents its ASCII value. This need not be true. — Alok Singhal
– Alok Singhal, Commented Jan 12, 2010 at 2:41

codaddict · Accepted Answer · 2010-01-12 02:34:31Z

4

You have not initialized the lexicographical_values array. You can initialize it by doing:

int lexicographical_values[20] = {};

Every time you see big numbers in the output, check for uninitialized variables.

edited Jan 12, 2010 at 2:34

answered Jan 12, 2010 at 2:28

codaddict

457k83 gold badges501 silver badges537 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Draemon Over a year ago

Especially large negative numbers you weren't expecting

Trent Over a year ago

Since the total for a word should never be a negative value perhaps lexicographical_values should be an array of unsigned int's rather than ints

iBiryukov Over a year ago

Thanks a lot. This worked! I was wondering about array initialisation but didn't believe that a loop would be an elegant solution.

Michael Burr Over a year ago

Nitpick note: the empty braces will work in C++, but for C (unless the compiler is using a language extension) there needs to be at least one const for the 1st item (the remainder will be zero-initialized), so this needs to be int lexicographical_values[20] = {0};

bmargulies · Accepted Answer · 2010-01-12 02:27:09Z

2

You're starting with uninitialized memory.

man memset

answered Jan 12, 2010 at 2:27

bmargulies

101k40 gold badges196 silver badges327 bronze badges

Comments

score 0 · Accepted Answer · 2010-01-12 02:52:04Z

You have not initialized the char_array with anything, so most likely it has garbage (depends on compiler options and platforms) so, you do a strlen(char_array) and at this point we're not sure what we're going to get out of it. If you initialize it with 0s (like: char char_array[100] = {0}; then strlen will return 0 and you'll never enter the loop.

Maybe you're looking for sizeof() here?

Oh, yes, forgot to mention that you need to initialize the second array also as was already pointed out.

Collectives™ on Stack Overflow

C ints and chars. Strange behavior

3 Answers 3

4 Comments

Comments

Comments

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

4 Comments

Comments

Comments

Related