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 = ; 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>; i--) {
     [newStr appendString:[str  substringWithRange:NSMakeRange(i-, )]];
 }
 return newStr;