下面

对下面程序描述正确的是(   )。 #include #include  void main()   {FILE *in,*out; if((in=fopen("file1.txt","a+"))==NULL)     {printf("cannot open file1\n");        exit(0);      }if((out=fopen("file2.txt","a+"))==NULL)  

对下面程序描述正确的是(   )。 #include #include  void main()   {FILE *in,*out; if((in=fopen("file1.txt","a+"))==NULL)     {printf("cannot open file1\n");        exit(0);      }if((out=fopen("file2.txt","a+"))==NU

如图所示,光滑轻绳AB穿过系有重物的小环,当绳两端固定在同一水平高度时,小环恰在绳的中点O,并达到平衡现保持A端不动,将B端在同一水平高度缓慢向右平移,则在B端平衡的过程中,绳OA、OB段所受拉力FOA和FOB的变化是(  ).

如图所示,光滑轻绳AB穿过系有重物的小环,当绳两端固定在同一水平高度时,小环恰在绳的中点O,并达到平衡现保持A端不动,将B端在同一水平高度缓慢向右平移,则在B端平衡的过程中,绳OA、OB段所受拉力FOA和FOB的变化是(  ).

下面程序的运行结果是(   )。#includemain(){ FILE *fp;  int a=2,b=4,c=6,k,n;  fp=fopen("test.dat","w"); fprintf(fp,"%d\n",a); fprintf(fp,"%d %d\n",b,c); fclose(fp); fp=fopen("test.dat","r"); fscanf(fp,"%

下面程序的运行结果是(   )。#includemain(){ FILE *fp;  int a=2,b=4,c=6,k,n;  fp=fopen("test.dat","w"); fprintf(fp,"%d\n",a); fprintf(fp,"%d %d\n",b,c); fclose(fp); fp=fopen("test.dat","r"); fscanf(fp,"%