从 UIPicker 中提取 NSString 后 NSString 转换为 doubleValue
我有：
NSInteger dollarrow = [ValuesPicker selectedRowInComponent:kDollar];
NSString *dollar = [dollarlist objectAtIndex:dollarrow];
double converteddollar=0;
我想对此进行 for 循环并获取 double 中的值，我正在尝试这样做：
for(dollar=1;dollar<=99;dollar++)
{
converteddollar = converteddollar + 2;
}
现在美元包含 NSString 我如何转换为 double 才能成功执行操作，然后
NSString *message = [[NSString alloc] initWithFormat:@"%0.2f",converteddollar];
我收到警告，并且应用程序是崩溃..我该如何纠正它。 我正在学习 Objective C 请帮忙。 谢谢 。 抱歉，我不想 == 我只是想使用 =
I have :
NSInteger dollarrow = [ValuesPicker selectedRowInComponent:kDollar];
NSString *dollar = [dollarlist objectAtIndex:dollarrow];
double converteddollar=0;
I want to do a for loop on this and get the value in double , I am trying this :
for(dollar=1;dollar<=99;dollar++)
{
converteddollar = converteddollar + 2;
}
Now the dollar contains NSString how do I convert into double to do the operation successfully and then
NSString *message = [[NSString alloc] initWithFormat:@"%0.2f",converteddollar];
I am getting warnings and the app is crashing .. How can I correct it .
I am learning Objective C please help .
Thankyou .
Sorry I did not want == i just wanted to use =
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评论（3）
你的 for 循环是错误的。你真的想要'=='吗？我猜你只想要“=”。你不能使用这样的东西吗？ （我只是举一个例子来指出循环中的错误。您的要求可能有所不同。而且我还没有编译代码，现在没有mac。所以您可能会遇到一些小错误）
double sum = 0 for (NSInteger i = 1; i <= 99; i++) { sum += 2; // or whatever you need here } NSString *convertedStr = [NSString stringWithFormat:@"%lf", sum];Your for loop is wrong. Are you really want '=='? I guess you want only '='. Can't you use something like this? (I'm just giving an example to point the mistakes in loop. Your requirement may be something different. And also I have not compiled the code, don't have mac with me right now. So you may get some minor mistake)
double sum = 0 for (NSInteger i = 1; i <= 99; i++) { sum += 2; // or whatever you need here } NSString *convertedStr = [NSString stringWithFormat:@"%lf", sum];很多错误...
selectedRowInComponent:方法是一个成员方法。不是静态的。您需要在实例上调用它。==是比较运算符。您想要的当然是一个带有单个=符号的赋值。您声明一个指向 NSString 对象的指针。但它尚未初始化。
您还应该在循环中使用临时双变量。
我不明白你的循环应该做什么。你能解释一下吗？
Lots of errors...
The
selectedRowInComponent:method is a member method. Not a static one. You need to call it on an instance.==is a comparison operator. What you want is certainly an assignment, with a single=sign.You declare a pointer to a NSString object. But it's not initialized.
You should also use a temporary double variable for your loop.
I don't understand what your loop is supposed to do. Can you explain a little bit?
NSString *dollar = [dollarlist objectAtIndex:dollarrow];double conversiondollar = [dollar doubleValue];应该可以工作（不需要for循环）NSString *dollar = [dollarlist objectAtIndex:dollarrow];double converteddollar = [dollar doubleValue];should work (no need for youforloop)