oc－－习题

1.取出符串“123-456-789-000”中的数字部分，组成一个新的字符串输出

 NSString *str=[[NSString alloc]initWithFormat:@"123-456-789-000"];
        
        //(1)把”－“去掉，并放在数组内  并输出
        NSArray *arr=[str componentsSeparatedByString:@"-"];
        NSLog(@"%@%@%@%@",[arr objectAtIndex:0],[arr objectAtIndex:1],[arr objectAtIndex:2],[arr objectAtIndex:3]);
        //(2)用空字符代替“－“
        NSString *newStr=[str stringByReplacingOccurrencesOfString:@"-" withString:@""];
        NSLog(@"%@",newStr);

2.放四个十进制三位数到一个数组中，然后按从小到大排序后组成一个新的数组

#import <Foundation/Foundation.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSMutableArray *arr=[[NSMutableArray alloc]initWithObjects:@"123",@"234",@"110",@"142", nil];
        for(int i=0;i<[arr count]-1;i++){
            for(int j=0;j<[arr count]-i-1;j++){
                NSComparisonResult result=[[arr objectAtIndex:j] compare:[arr objectAtIndex:j+1]];
                if(result==NSOrderedDescending){
                 [arr exchangeObjectAtIndex:j+1 withObjectAtIndex:j];
                }
            }
        }
        for(int i=0;i<[arr count];i++){
            NSLog(@"%@",[arr objectAtIndex:i]);
        }
    }
    return 0;
}