可能会用到

输入的字符串转换为数字

- (float)Transform:(NSMutableString *)str {
    int flag = 0, zhen = 1;
    float sum = 0, temp = 0, t = 0.0;
    if ([str characterAtIndex:0] == '-') {
        zhen = 0;
    } else {
        temp = (int)[str characterAtIndex:0] - 48;
    }
    if ([str length] > 1) {
        for (int i = 1; i < [str length]; i++) {
            if ([str characterAtIndex:i] == '.') {
                sum += temp;
                temp = 0.1 * ((int)[str characterAtIndex:++i] - 48);
                t = 0.01;
                flag = 1;
                continue;
            } else {
                if (flag == 0) {
                    temp = temp * 10 + (int)[str characterAtIndex:i] - 48;
                } else {
                    temp = temp + t * ((int)[str characterAtIndex:i] - 48);
                    t = 0.1 * t;
                }
            }
        }
        sum += temp;
    } else {
        sum = (int)[str characterAtIndex:0] - 48;
    }
    if (zhen == 0) {
        return sum * (-1);
    } else {
        return sum;
    }
}