string is an array of characters ?

[YosofShihsbi]

we all know that string variables are characters arrays , so while we can assign value to char array very simply by :

  char x[10];
  x[5]=48;

but in string case this is no work !
here is this code , in char case it's working , but in string case it's not !

#include<iostream>
#include<string>
using namespace std;
int main()
{
	//Char case
	char x[10];
	for(int i=0;i<10;i++)
		x[i]=i+48;
	for(int i=0;i<10;i++)
		cout<<x[i]<<endl;

	//string case
	string str;
	for(int i=0;i<10;i++)
		str[i]=i+48;
	for(int i=0;i<10;i++)
		cout<<x[i]<<endl;
}

[Peter87]

In the "string case" you have an empty string. If you want the string to have 10 chars you should say so.

// Creates a string of length 10 with all characters set to '*'.
string str(10, '*');

http://en.cppreference.com/w/cpp/string/basic_string/basic_string

[YosofShihsbi]

but in the char array it's empty too !
why I have to fill string array with "*" ,and in char I haven't ?
remember that string has default size , you can see from :

#include<iostream>
#include<string>
using namespace std;
int main()
{
	string str;
	cout<<str.max_size()<<endl; //it returns 4294967294
}

[Peter87]

but in the char array it's empty too !

No, an array can't be empty.

// x is an array of 10 characters,
// the values of these chars are undefined.
char x[10];

why I have to fill string array with "*" ,and in char I haven't ?

You can use any other character you want. I just picked '*' out of the air because if I specify the size of the string in the constructor I also have to specify their value. I could also have used the resize function.

string str;
str.resize(10);
// which is equivalent to
string str(10, '\0');

remember that string has default size

The default size of a string is zero. The max_size() function just gives you an upper limit to what sizes can be handled. 4294967294 is the highest value that can be stored in an unsigned 32-bit number. In a 32-bit address space you will likely run into problems way before reaching that size because the string is not the only thing that use up memory.

[YosofShihsbi]

Thank You!