@interface NSMutableString (extension)
-(void)quChuKongGe;
-(int)countNum;
@end
//去除首位的空格,并将最后一个字符改为*
//统计英文字符的个数
@implementation NSMutableString (extension)

-(void)quChuKongGe{
    //去除首尾的空格
   [self setString:[self stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]]];
    //将最后一个字符变为*
    [self replaceCharactersInRange:NSMakeRange(self.length-1, 1) withString:@"*"];
}
-(int)countNum{
    int count=0;
    for (int i=0; i<self.length; i++) {
        unichar ch=[self characterAtIndex:i];
        if((ch>='A'&&ch<='Z')||(ch>='a'&&ch<='z')){
            count++;

        }
#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
   
    @autoreleasepool {
        NSMutableString *str=[NSMutableString stringWithFormat:@"   jjdhsggd  "];
        [str quChuKongGe];
        NSLog(@"%@",str);
        int num=[str countNum];
        NSLog(@"%d",num);
        
        
        
    }
    return 0;

    }
    return count;

}

协议这块应该是相当重要的