C语言基础回顾与Objective-C核心类型详解-EW帮帮网

int age = 25;                   // 整型
float height = 1.75f;           // 单精度浮点
double pi = 3.1415926535;       // 双精度浮点
char initial = 'J';             // 字符型
BOOL isStudent = YES;           // Objective-C特有的布尔类型(YES/NO)

2. 运算符

// 算术运算符
int sum = a + b;
int diff = a - b;
int product = a * b;
float quotient = (float)a / b;

// 比较运算符
if (a == b) { /* ... */ }
if (a > b) { /* ... */ }

// 逻辑运算符
if (condition1 && condition2) { /* ... */ }
if (condition1 || condition2) { /* ... */ }

3. 控制流

// if-else
if (score >= 90) {
    grade = 'A';
} else if (score >= 80) {
    grade = 'B';
} else {
    grade = 'C';
}

// for循环
for (int i = 0; i < 10; i++) {
    printf("%d\n", i);
}

// while循环
while (condition) {
    // 循环体
}

// do-while循环
do {
    // 至少执行一次
} while (condition);

4. 数组与结构体

// 数组
int numbers[5] = {1, 2, 3, 4, 5};
numbers[0] = 10;

// 结构体
struct Person {
    char name[50];
    int age;
};
struct Person p1 = {"John", 30};

二、Objective-C核心类型详解

1. NSString - 字符串处理

创建字符串：

NSString *greeting = @"Hello, Objective-C!";
NSString *name = [[NSString alloc] initWithFormat:@"%@ %@", firstName, lastName];

常用方法：

// 获取长度
NSUInteger len = [greeting length];

// 子字符串
NSString *sub = [greeting substringFromIndex:7]; // "World!"
NSString *subRange = [greeting substringWithRange:NSMakeRange(0, 5)]; // "Hello"

// 比较
if ([str1 isEqualToString:str2]) {
    // 字符串内容相等
}

// 大小写转换
NSString *upper = [greeting uppercaseString];
NSString *lower = [greeting lowercaseString];

// 查找
NSRange range = [greeting rangeOfString:@"World"];
if (range.location != NSNotFound) {
    NSLog(@"Found at index %lu", range.location);
}

2. NSNumber - 基本类型对象化

创建NSNumber：

NSNumber *intNum = @42;
NSNumber *floatNum = @3.14f;
NSNumber *doubleNum = @3.1415926535;
NSNumber *boolNum = @YES;

转换回基本类型：

int i = [intNum intValue];
float f = [floatNum floatValue];
BOOL b = [boolNum boolValue];

3. NSArray - 有序集合

不可变数组(NSArray)：

NSArray *colors = @[@"Red", @"Green", @"Blue"];
id firstColor = colors[0];  // 或者 [colors objectAtIndex:0]
NSUInteger count = [colors count];

// 遍历
for (NSString *color in colors) {
    NSLog(@"%@", color);
}

// 包含检查
if ([colors containsObject:@"Green"]) {
    NSLog(@"包含绿色");
}

可变数组(NSMutableArray)：

NSMutableArray *mutableColors = [NSMutableArray arrayWithArray:colors];
[mutableColors addObject:@"Yellow"];
[mutableColors insertObject:@"Black" atIndex:0];
[mutableColors removeObject:@"Red"];
[mutableColors removeObjectAtIndex:1];

4. NSDictionary - 键值对集合

不可变字典(NSDictionary)：

NSDictionary *person = @{
    @"name": @"John",
    @"age": @30,
    @"isStudent": @NO
};

NSString *name = person[@"name"];  // 或者 [person objectForKey:@"name"]

可变字典(NSMutableDictionary)：

NSMutableDictionary *mutablePerson = [NSMutableDictionary dictionaryWithDictionary:person];
[mutablePerson setObject:@"Doe" forKey:@"lastName"];
[mutablePerson removeObjectForKey:@"isStudent"];

5. nil与NULL的区别

NULL是C语言的空指针
nil是Objective-C对象的空指针
现代Objective-C中，两者基本可以互换，但约定俗成：
- 对象用nil
- 普通指针用NULL

NSString *str = nil;  // Objective-C对象
int *ptr = NULL;      // C指针

三、动手实践

1. 字符串操作示例

        NSString *firstName = @"SCC";
        NSString *lastName = @"Shuaici";

        // 字符串拼接
        NSString *fullName = [NSString stringWithFormat:@"%@==>%@", firstName, lastName];
        
        // 字符串分割
        NSArray *components = [fullName componentsSeparatedByString:@"==>"];
        
        // 字符串替换
        NSString *modified = [fullName stringByReplacingOccurrencesOfString:@"Shuaici" withString:@"Shuaici-SVIP"];

2. 数组操作示例

// 创建数组
NSArray *originalArray = @[@1, @2, @3, @4, @5];

// 映射
NSMutableArray *squaredArray = [NSMutableArray array];
for (NSNumber *num in originalArray) {
    [squaredArray addObject:@([num intValue] * [num intValue])];
}

// 过滤
NSPredicate *evenPredicate = [NSPredicate predicateWithFormat:@"modulus:by:(SELF, 2) == 0"];
NSArray *evenNumbers = [originalArray filteredArrayUsingPredicate:evenPredicate];

// 排序
NSArray *sorted = [originalArray sortedArrayUsingSelector:@selector(compare:)];

3. 字典操作示例

// 创建字典
NSMutableDictionary *employee = [NSMutableDictionary dictionary];
[employee setObject:@"Shuaici" forKey:@"name"];
[employee setObject:@30 forKey:@"age"];
[employee setObject:@"Developer" forKey:@"position"];

// 更新值
[employee setObject:@31 forKey:@"age"];

// 遍历
for (NSString *key in employee) {
    NSLog(@"%@: %@", key, employee[key]);
}

// 字典转JSON
NSData *jsonData = [NSJSONSerialization dataWithJSONObject:employee options:NSJSONWritingPrettyPrinted error:nil];
NSString *jsonString = [[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];

四、总结

Objective-C在C语言基础上引入了丰富的面向对象特性，其中核心类型如NSString、NSNumber、NSArray和NSDictionary是日常开发中最常用的类。理解这些类型的特点和用法是掌握Objective-C开发的基础。不可变类型(NSString, NSArray, NSDictionary)和它们的可变版本(NSMutableString, NSMutableArray, NSMutableDictionary)之间的区别尤其重要，这关系到代码的安全性和性能。

C语言基础回顾与Objective-C核心类型详解

一、C语言基础快速回顾

1. 基本数据类型