Binary to Decimal and reverse

[ylxin1993]

I see these two question in my book, the first one I make it out, but the second one puzzles me, how ?
12.8.5 Binary to Decimal
Write a program that asks the user to input a binary string (e.g., “11100010101”). Note that the input is a string, not a number. The string specifies a binary number. The program then is to convert the binary number which the string specifies into a decimal number and output the result. Your output should look like this:

Enter a binary string: 101
101 = 5 in decimal. 
Press any key to continue. 

12.8.6 Decimal to Binary
Write the reverse conversion of Exercise 12.8.5. That is, write a program that asks the user to input a decimal number (this time it is not a string but a number). The program then is to convert the decimal number which the user entered into a binary string(e.g., “11100010101”) and output the result. Your
output should look like this:

Enter a decimal number: 14
14 = 1110 in binary. 
Press any key to continue. 

[ylxin1993]

here's my Binary to Decimal:

int BinToDec(string s);
int main() {
	string s;
	cout << "enter string by binary: " << endl;
	getline(cin, s);
	int result = BinToDec(s);
	cout << "decimal: " << result << endl;
	system("pause");
	return 0;
}

int BinToDec(string s) {
	int len = s.length();
	int result = 0;
	for(int i = 0; i < len; i++) {
		int pow = 0;	
		if(s[i] == '1') {
			pow = 1;
			for(int j = 0; j < (len - i -1) ; j++)
				pow *= 2;
		}
		result += pow;
	}
	return result;
}

[ylxin1993]

I also want to know that the binary output must be a string ?
if not, can you guys give me some examples to do the conversion?

[andywestken]

Does your decimal have to be a string, too? Edit: reread the orig. post...

[vlad from moscow]

1.

std::string binary_string b( "11100010101" );
 
std::cout << std::accumulate( binary_string.begin(), binary_string.end(), 0u,
                              []( unsigned int s, char c ) { return ( 2 * s + ( c -'0' ) ); } )
              << std::cout; 

2.

[code]unsigned int x = UINT_MAX;
std::string binary_string;

do { binary_string.push_back( x % 2 + '0' ); } while ( x /= 2 );
std::reverse( binary_string.begin(), binary_string.end() );

std::cout << UINT_MAX << " = " << binary_string << std::endl;