2019-10-10练习

1，交换两个数组的内容
#include<stdio.h>
#include<windows.h>
int main()
{
int a[5] = { 1, 2, 3, 4, 5 },
 b[5] = { 6, 7, 8, 9, 10 }, 
c[5], i = 0;
for (; i < 5; i++)
{
c[i] = b[i]；
b[i] = a[i];
a[i] = c[i];
printf("%d %d\n", a[i], b[i]);
}
system("pause");
return 0;
}

2，求1/1-1/2+1/3-1/4+.....
.....-1/100的和
#include<math.h>
int main()
{
int k = -1, a = 0;
float sum = 0 ,b=1,c=0;
while (c<=99)
{
int a = pow(k, c);
sum = sum + (b/(c+1))*a;
c++;
}
printf("%f\n", sum);
system("pause");
return 0;
}

3求1——100的整数中9
出现的次数
#include<stdio.h>
#include<windows.h>
int main()
{
int i = 1, a=0,sum = 0;
for (; i <= 100; i++)
{
if (9== i % 10)
{
sum += 1;
if (9 == i / 10)
{
sum += 1;
}
}  
}
printf("%d\n",sum);
system("pause");
return 0;
}