OC字符串内字母大小写转换

默认系统函数：
lowercaseString转小写
uppercaseString转大写

-(NSString *)toLower:(NSString *)str{
    
    
    for (NSInteger i=0; i<str.length; i++) {
    
    
        if ([str characterAtIndex:i]>='A'&[str characterAtIndex:i]<='Z') {
    
    
            //A  65  a  97
            char  temp=[str characterAtIndex:i]+32;
            NSRange range=NSMakeRange(i, 1);
            str=[str stringByReplacingCharactersInRange:range withString:[NSString stringWithFormat:@"%c",temp]];
        }
    }
    return str;
}
 
-(NSString *)toUpper:(NSString *)str{
    
    
    for (NSInteger i=0; i<str.length; i++) {
    
    
        if ([str characterAtIndex:i]>='a'&[str characterAtIndex:i]<='z') {
    
    
            //A  65  a  97
            char  temp=[str characterAtIndex:i]-32;
            NSRange range=NSMakeRange(i, 1);
            str=[str stringByReplacingCharactersInRange:range withString:[NSString stringWithFormat:@"%c",temp]];
        }
    }
    return str;
}