atof的简单实现

#include <iostream>
#include <stdio.h>
using namespace std;
float My_atof(char str[]);
int main()
{
	char str[10] = "+34.5";
	float num;
	num = My_atof(str);
	cout<<num<<endl;
	return 0;
	

}
float My_atof(char str[])
{
	int i, j, sign, temp = 1;
	float val;
	for(i = 0; isspace(str[i]); i++);
	sign = (str[i] == '-') ? -1 : 1;
	if(str[i] == '+' || str[i] == '-') 
		i++;
	for(val = 0; isdigit(str[i]); i++)
		val = val * 10 + str[i]-'0';
	if(str[i++] == '.')
	{
		val = val*10 +str[i] - '0';
		temp *=10;
	}
	return val * sign / temp;
}

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