Question about strings and floats

Hi everyone.

i have 3 questions, the first one is:
why isnt this possible:

Code:

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char a[10];
a="Hello";

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and this is:

Code:

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char *a;
a="Hello"

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??

i know that when i call both variables they both point to a[0] then why cant the first one work as the 2º one (but of course, it would store less chars)??

the 2 q:
why does this: char *a="TESTING TESTING" takes the same space as this: char *a=" " (both take only 4 bytes. and why does this: char a[10] takes 10 bytes. i know that one automaticaly reserves space for 10 chars and the other one doest, but how can we store like... 10 chars in 4 bytes??

the 3 q:
how is a float number like 24,123342 represented in bits? and why does a number like 3*10^20 only takes 4 bytes of space?? (the same as an integer).


Help pls, those may be stupid questions for some but those things dont make sence to me yet.
tks.

ANS:
(1)In char a[10] , a is a constant.So you just can not assign "Hello" to it with "=".The second one "a" is a string pointer variable,so you can do it.
(2)Well the string pointer "a" points to is stored in the constant memory area, and pointer "a " points to the first character of the string. The 4 bytes which is the result of sizeof(a) is just the size of an integer pointer,not the size of the string.
(3)The same as (2).

(1) a is an array. You can't assign to an array.

(2) a is a pointer. The string literal also decays to a pointer to the first character. However, a string literal is read-only. Therefore you should only point const pointers to it.

Code:

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const char* a = "hello";

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If you want a modifiable C-style string:

Code:

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char a[10] = "hello";
//or
char a[] = "hello"; //necessary size deduced from the initialization

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If you can't use initialization, then you should use the strcpy library function to copy a string into an array:

Code:

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char a[10];
strcpy(a, "hello");

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(3) You should read about floating point numbers. Short answer: an int stores the number exactly, a floating point represents an approximation of the value and has limited precision. For example, a float will not store a value like 3.45629385648392038460039281 * 10 ^ 50 exactly; some of the precision will be lost and you'll rather end up storing 3.45629385648 * 10 ^ 50.

Ok tks for the quick answers