格式化输出，%n.m

void main()
{
float a=3.1415926;
int b=2;
printf("float=%f\n",a);
printf("float=%.5f\n",a);
printf("float=%.4f\n",a);
printf("float=%2f\n",a);
printf("float=%5.2f\n",a);//总宽度是5，2位是小数
printf("float=%3.6f\n",a);//小数点后6位，超过3，则保持原数据不变
printf("b=%2d\n",b);
printf("b=%7d\n",b);
printf("b=%.5d\n",b);
system("pause");
}