rand srand iOS 随机数

//初始化化随机数发生器

srand((unsigned)time(0));

//产生1--100的随机数

rand() % 100+1;

//举例支付宝Demo产生的随机数

static int kNumber =15;

    

    NSString *sourceStr =@"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";

    NSMutableString *resultStr = [[NSMutableStringalloc] init];

    srand((unsigned)time(0));

   for (int i =0; i < kNumber; i++)

    {

        unsigned index = rand() % [sourceStr length];

        NSString *oneStr = [sourceStr substringWithRange:NSMakeRange(index, 1)];

        [resultStr appendString:oneStr];

    }

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