随机字母和数字

//返回16位大小写字母和数字

+(NSString*)return16LetterAndNumber{//定义一个包含数字，大小写字母的字符串NSString*strAll=@"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";//定义一个结果NSString*result=[[NSMutableString alloc]initWithCapacity:16];for(inti=0;i<16;i++){//获取随机数NSInteger index=arc4random()%(strAll.length-1);chartempStr=[strAll characterAtIndex:index];result=(NSMutableString*)[result stringByAppendingString:[NSString stringWithFormat:@"%c",tempStr]];}returnresult;}