Foundation框架的一些实用方法:替换字符串,去空格,反转

//定义一个可变字符串, Format后面可以跟字符串类型,也可以传入C语言的字符串数组
NSMutableString *str = [NSMutableString stringWithFormat:@"<#NSString#>"];

// 获取NSMutableString或NString 某位置的字符
NSMutableString *newS1=[NSMutableString stringWithString:s1];
for (int i = 0; i<s1.length; i++) {
    char c1 = [newS1 characterAtIndex:i]; // 用c1去接收了newS1 i 位置的字符
}

//初始化一个NSArray
NSMutableArray *arr = [NSMutableArray array];
//给数组arr增加元素
[arr addObject:xxx]

//定义一个字典
NSMutableDictionary *dict1 = [NSMutableDictionary dictionaryWithDictionary:@{<#@"k1":@"v1",@"k2":@"v2"#>}];

//  替换字符串
NSMutableString *str = [NSMutableString stringWithFormat:@"123iositheimaios"];
NSString *newStr =  [str stringByReplacingOccurrencesOfString:@"ios" withString:@"andriod"];

// 去空格
+(NSString *)removeSpace:(NSString *)s{
    NSString *newStr = [s stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    return newStr;
}

// 字符串反转 
unsigned long len = str.length;
NSMutableString *newStr;
for (unsigned long i=len; i>0; i--) {
    [newStr appendString:[str  substringWithRange:NSMakeRange(i-1, 1)]];
}
return newStr;