why when we build an array like this:

char st[]="abcd";

we have 5 cells in which the last cell is \0

why is that

and what are the number of each cell

is it from 0-4

or 1-5 ??

Because at the lowest level, a string in C is just a sequence of characters. And since the length of the string isn't stored anywhere, you need a different way to tell where the end of the string is. So every string in C is terminated by a NULL character (\0), in most cases.

In your example,

Code:

char st[]="abcd";

you're right that st has five elements, and that the last one is \0. Since C starts counting from zero, these elements will be [0] through [4], and st[4] will be the \0.

so every array ends with \0 cell ??

so every array ends with \0 cell ??

No, every string ends with a '\0', but strings are arrays of characters.

Just an example: strlen calculates the length of a string. It does this by checking every character in the array for '\0' and counts upwards. When it finds '\0', it can return the length.

thanks i understand now