问题1：
        int n,n1,n2,n3,n4;
        n1=n2=n3=n4=2;
        n=n1+1,n2+2,n3+3,n4+4;
        printf("n=%d\tn1=%d\tn2=%d\tn3=%d\tn4=%d\n",n,n1,n2,n3,n4);//输出为何是3  2  2  2  2？
        n=(n1+1,n2+2,n3+3,n4+4);
        printf("n=%d\tn1=%d\tn2=%d\tn3=%d\tn4=%d\n",n,n1,n2,n3,n4);//输出为何是6  2  2  2  2？
        n=n1=n2=n3=2;
        printf("n1=%d\tn2=%d\tn3=%d\n",n1=n+1,n2=n1+1,n3=n2+1);//输出为何是3  3  3？
        n=n1=n2=n3=2;
        printf("n3=%d\tn2=%d\tn1=%d\n",n3=n2+1,n2=n1+1,n1=n+1);//输出为何是5  4  3？

问题2：

                int x;
                int y=1;
                int z=-1;
                if(z<0)
                        if(z=y<0)-------------------if(z=y<0)这个语句什么意思？

                                x=3;
                        else if(y==0)
                                x=5;
                        else
                                x=7;
                        printf("x=%d\t",x);-----//为何输出7？
                        printf("z=%d\n",z);----//为何输出0？
                        if(x=z=y)
                                x=3;
                        printf("x=%d\t",x);----//为何输出3？
                        printf("z=%d\n",z);---//为何输出1？