Counting the number of elements in an array - C - c

Question

I am trying to count the number of elements in an array using C. I tried out the following code. But it just returns 83 every time I run the program. What I mean by to count the number of elements is that I need to know the number of elements that we have entered and not the size of the array.
#include<stdio.h>
#include<stdlib.h>
main(){
int a[100], j = 0, i;
a[0] = '0';
a[1] = '1';
a[2] = '2';
a[3] = '3';
a[4] = '4';
a[5] = '5';
for(i=0; i<100; i++){
if(a[i] == '\0'){
}
else
j = j + 1;
}
printf("%d", j);
system("pause");
}

Answer 1

Arrays in C are a fixed size. They do not expand. Your array has two entries; writing to array[2], array[3], etc. invokes undefined behaviour. In other words, it's invalid code.
If you want to be able to insert an arbitrary number of elements, you will need to use dynamically-allocated memory, manually track how many elements you've inserted, and use realloc when you need to resize.

Answer 2

Since the OP amended his code, here is a more correct reply:
This code works 'by chance', since you didn't initialize the array previously.
It's just 'luck', that somewhere in there, the value 0 comes up.
The declaration of an array does NOT zero it.
Use:
memset(a, 0, 100);
For that. That way, the first 'not overwritten' byte will return '0'.
Reference: http://www.cplusplus.com/reference/clibrary/cstring/memset/
Alternatively, you have to set the 'delimited' manually by adding a[x] = 0;
Now, I know you specifically asked for a 'C' solution, but if you would like to consider using a C++-Compiler, I suggest looking at the stl of C++.
Here's a link to get you started: http://www.cplusplus.com/reference/stl/list/
It's initialized as:
list<char>List;
List.push_back(1);
List.push_back(2);
List.push_back('a');
int j = List.size(); //Returns '3'

Answer 3

do this instead:
main(){
int a[100] = {0};
int j = 0;
int i = 0;
// other stuff

Answer 4

Update based on new code:
In general, you will need a way to identify the end of your array in order to do a correct count. For strings the '\0' is used generally. For other data types you have to come up with your own value to check.
For your specific code example above:
You need to insert a \0 yourself into your array in the last position so that your count will work. (When you create a string like "hello", the '\0' gets automatically put in for you at the end of the string, but not if you create a string character by character).
Alternatively, check for the character '5' to find the end of your current array of characters.
Also, you should break out of the loop once you found the last character, otherwise you are going past the end of the array and will most likely crash (again, if you don't it's sheer luck). I.e., something like:
if(a[i] == '\0'){
break;
}
will work if you do:
a[6] = '\0';
before.
Since C doesn't check array bounds, it might appear that with your current code you seemingly get away with this, but it's sheer luck that the program doesn't crash and may change from run to run. In other words, this is undefined behavior.
Finally, you can of course also use strlen() if you are dealing with strings.