String to floating point decimal

#include <iostream>
#include <cctype>
#include <cstdlib>
using namespace std;

/*
 *	stof by Jakash3
 *	Converts a string to floating point decimal using
 *	specified floating point type template
 *	The string should be in the form:
 *	[+-]?[0123456789].([.][0123456789]+)?[ ]*([eE][+-]?[0123456789]+)?
 *
 *	Example strings:
 *	25, 3.5, 3.500, 3.5e6, 3.5 e-5, 3.5E5, 3.5E-4, 3.5 e+8
 */
template <typename T>
T stof(const char* s) {
	T val = 0;			/* Integer part */
	T frac = 0;			/* Fractional part */
	bool neg = false;	/* Sign flag */
	
	/* Skip whitespace */
	while (isspace(*s)) s++;
	
	/* Check for sign */
	if (*s == '-') { neg = true; s++; }
	else if (*s == '+') s++;
	
	/* Read integer part */
	while (isdigit(*s))
		val = val * 10 + (*(s++) - '0');
	
	/* Read fractional part */	
	if (*s == '.') {
		T q;
		for (s++; isdigit(*s); s++); s--;
		do {
			q = *s - '0';
			frac = frac / 10 + q / 10;
		} while (isdigit(*(--s)));
		while (isdigit(*(++s))) s++;
	}
	
	/* Skip whitespace */
	while (isspace(*s)) s++;
	
	/* Combine integer and fractional part, and apply sign */
	val += frac;
	if (neg) val *= -1;
	
	/* Process E notation */
	if (*s == 'e' || *s == 'E') {
		int j = atoi(++s);
		if (j == 0) return val;
		for (int i = 0; i != j; (j > 0) ? i++ : i--)
			(j > 0) ? val *= 10 : val *= -10;
	}
	
	return val;
}

int main() {
	float f;
	string s;
	cout << "Enter float: ";
	getline(cin, s);
	cout << "You entered " << stof<float>(s.c_str()) << endl;
}