include<stdio.h>

int main()
{
char c;
int l = 0, s = 0, d = 0, o = 0;
printf("请输入一行字符：\n");
while ((c = getchar()) != '\n')
{
if (c >= 'a'&&c <= 'z' || c >= 'A'&&c <= 'Z')
l++;
else if (c == ' ')
s++;
else if (c >= '0'&&c <= '9')
d++;
else
o++;
}
printf("字母数：%d,空格数：%d,数字数：%d,其余数：%d", l, s, d, o);
return 0;
}

include<stdio.h>

int main()
{
int n,s1,s2,i,j,k;
s1 = 0; s2 = 0; k = 1;
scanf("%d", &n);
for (i = 1; i <= n; i++)
{
for (j = 1; j <= i; j++)
{

        s1 = k * 2 + s1;
        k = 10 * k;
    }
    s2 = s1 + s2;
}
printf("result is %d\n", s2);
return 0;

}

include<stdio.h>

int main()
{
float j,k,i,s1,s2,s3;
s1 = 0; s2 = 0; s3 = 0;
for (k = 1; k <= 100; k++)
{
s1 = s1 + k;
}
for (i = 1; i <= 50; i++)
{
s2 = s2 + i*i;
}
for (j = 1; j <= 10; j++)
{
s3 = s3 + 1 / j;
}
printf("total number is %f.\n", s1 + s2 + s3);
return 0;
}

include<stdio.h>

int main()
{
int t,t1,t2,t3;
for (t = 100; t <= 999; t++)
{

    t1 = t / 100;
    t2 = t / 10 % 10;
    t3 = t % 10;
    if (t1*t1*t1 + t2*t2*t2 + t3*t3*t3 != t) continue;
    printf("水仙数有：%d.\n", t);
}
return 0;

}

include<stdio.h>

int main()
{
double i,j, k,a,b,sum;
j = 1; k = 2; sum = 2;
for (i = 1; i <= 19; i++)
{
a = j + k;
b = a / k;
j = k;
k = a;

    sum = sum + b;
}
printf("sum: %.2f\n", sum);
return 0;

}

include<stdio.h>

int main()
{
float i,s,h;
s = 100; h = s/2;
for (i = 2; i <= 10; i++)
{
s = s+2*h;
h = h / 2;
}
printf("total distance is %f.\n", s);
printf("10th hight is %f.\n", h);
return 0;
}

include<stdio.h>

int main()
{
int i, j;
printf("甲队A、B、C队员编号为1、2、3；乙队同理为1、2、3\n");
for (i = 1; i <= 3; i++)
{
for (j = 1; j <= 3; j++)
{
if ((i == 1 && j == 1)||(i==3&&j==1)||(i==3&&j==3)) continue;
printf("甲队%d号对阵乙队%d号\n", i, j);

    }
}
return 0;

}
关于17题的标准答案：

include<stdio.h>

int main()
{
char i, j, k;
for (i = 'x'; i <= 'z'; i++)
for (j = 'x'; j <= 'z'; j++)
if (i != j)
for (k = 'x'; k <= 'z'; k++)
if (i != k&&j != k)
if (i != 'x'&&k != 'x'&&k != 'z')
printf("A--%c\nB--%c\nC--%c\n", i, j, k);
return 0;
}