C语言入门_3

//交换两个数组的内容（两个数组一样长）

#include
#include
int main()
{
     int a[5] = {1, 2, 3, 4, 5};
     int b[5] = {6, 7, 8, 9, 10};
     int c[5] = {0};

     int i = 0;
     printf ("交换前：\na[i]:\t");
     for (i=0; i<5; ++i)
     {
          printf ("%d\t",a[i]);
     }
     printf ("\nb[i]:\t");
     for (i=0; i<5; ++i)
     {
          printf ("%d\t",b[i]);
     }
     printf ("\n");
     for (i=0; i<5; ++i)
     {
          c[i] = a[i];
          a[i] = b[i];
          b[i] = c[i];
     }
     printf ("交换后\na[i]:\t");
     for (i=0; i<5; ++i)
     {
          printf ("%d\t",a[i]);
     }
     printf ("\nb[i]:\t");
     for (i=0; i<5; ++i)
     {
          printf ("%d\t",b[i]);
     }
     printf ("\n");

     system ("pause");
     return 0;
}

//计算1/1-1/2+1/3-1/4+1/5 …… + 1/99 - 1/100 的值

#include

#include

int main()

{

    double i,j = 1;

    double sum = 0.0;

    for (i=1.0; i<=100.0; i++)
    {
         sum = sum + j/i;
         j = j * (-1);
    }

    printf ("%lf\n",sum);

    system ("pause");
    return 0;
}

//编写程序数一下 1到 100 的所有整数中出现多少次数字9。

#include

#include

int main()

{

    int i,count = 0;

    for (i=0; i<=100; ++i)
    {
        if (i%10 == 9)//个位为9
        {
            count ++;
        }
        if(i/10 == 9)//十位为9
        {
            count ++;
        }
    }
    printf ("%d\n",count);
    system ("pause");
    return 0;
}