@"%@",[arr objectAtIndex:i]);
// }
//
// 添加一个对象元素
[mulArray addObject:@"guoguo"];
?
// 交换下标对应的元素对象
[mulArray exchangeObjectAtIndex:0 withObjectAtIndex:[mulArray count]-1]; //交换第一个元素和最后一个元素
===================================================================================== 下面通过一个实例来形象的了解： 使用可变数组管理BOOk类，实现
图书的增删查改 BOOK有两个成员变量：_name,_price;
Book * book1 = [[Book alloc] initWithName:@"guozai1" andPrice:10];
Book * book2 = [[Book alloc] initWithName:@"guozai2" andPrice:15];
Book * book3 = [[Book alloc] initWithName:@"guozai3" andPrice:13];
?
//数组赋值
NSMutableArray *books = [NSMutableArray arrayWithObjects:book1,book2,book3, nil];
?
Book * book4 = [[Book alloc] initWithName:@"guozai4" andPrice:12];
?
//添加一本书
[books addObject:book4];
?
//删除一本书
[books removeObjectAtIndex:2];
?
for (int i = 0; i < [books count]; i ++) {
NSLog(@"%@,%.2f",[[books objectAtIndex:i] name],[[books objectAtIndex:i] price]);
}
?
?
//查找名字是guozai3的书,打印价格
for (int i = 0; i < [books count]; i ++) {
if ([[[books objectAtIndex:i] name] isEqualToString:@"guozai3"]) {
NSLog(@"%f",[[books objectAtIndex:i] price]);
}
}
?
// 对数组进行排序，按价格从高到低
for (int i = 0; i < [books count] - 1; i ++) {
for (int j = 0; j < [books count] - i - 1; j ++) {
if ([books[j] price] < [books[j+1] price]) {
[books exchangeObjectAtIndex:j withObjectAtIndex:j+1];
}
}
}
?
?
for (int i = 0; i < [books count]; i ++) {
NSLog(@"%@,%.2f",[books[i] name],[books[i] price]);
}
======================================================================================== 5.NSNumber:将基本数据类型转化成对象类型
//将基本数据类型int转化为对象类型
NSNumber * intNum = [NSNumber numberWithInt:100];//便利构造器
NSMutableArray * ar = [NSMutableArray arrayWithObjects:intNum, nil];
NSNumber * tem = [ar objectAtIndex:0];
?
//将对象类型转化成基本数据类型
int result = [tem intValue];
NSLog(@"%d",result);
======================================================================================== 6.NSValue：将结构体转化成对象
//将一个点转化成NSValue对象
NSPoint point = {1,2};
//将一个结构体转化成NSValue对象
NSValue *vPoint = [NSValue valueWithPoint:point];
?
//将vPoint转化成结构体
NSPoint point2 = [vPoint pointValue];
// NSLog(@"%.2f,%.2f",point2.x,point2.y);
?
// NSStringFromPoint可以将点转化成字符串
NSLog(@"%@",NSStringFromPoint(point2));
其他的例子类比就行：例如
?
//将NSsize结构体转化成NSValue对象
NSSize size = {22,44};
NSValue * sValue = [NSValue valueWithSize:size];
?
//将NSValue对象转化成NSSize结构体；
NSSize size2 = [sValue sizeva lue];
NSLog(@"%@", NSStringFromSize(size2));
========================================================================================