一.函數題

6-1 符號函數

int sign(int x)
{if (x > 0)return 1;else if (x == 0)return 0;elsereturn -1;
}

6-2 求排列數

double fact(int n)
{long long ret = 1;for (long long i = 1; i <= n; i++){ret =ret * i;}return ret;
}

6-3 求一個大于10的n位整數w的后n-1位的數，并作為函數值返回。

#include<math.h>
int fun(int w)
{int sum = 0;int count = 0;int num = w;while (num){num /= 10;count++;}sum = w % (int) (pow(10, count - 1));return sum;
}

6-4 其右上三角（含主對角線）元素之和。

int fun(int a[3][3])
{int sum1 = 0, sum2 = 0;for (int i = 0; i < 3; i++){for (int j = i; j < 3; j++){sum1 += a[i][j];}}return sum1;
} 

6-5 字符串比較

int fun(char a[], char b[])
{if (strcmp(a, b) < 0)return -1;else if (strcmp(a, b) > 0)return 1;elsereturn strcmp(a, b);
}

6-6 使用函數求素數和

int prime(int p)
{int count = 0;if(p==1)return 0;for (int i = 2; i <= p; i++){if (p % i == 0)count++;}if (count == 1)return 1;elsereturn 0;
}
int PrimeSum(int m, int n)
{int sum = 0;for (int i = (m<=n?m:n); i <= (n>=m?n:m); i++){if (prime(i) == 1)sum += i;}return sum;
}

6-7 使用函數輸出水仙花數

#include<math.h>
int narcissistic(int number)
{int count = 0;int sum1 = 0;int num = number;while (number){number /= 10;count++;}int sum = 0;number = num;while (number){sum1 = number % 10;sum += (int)(pow(sum1, count));number /= 10;sum1 = 0;}if (num == sum)return 1;elsereturn 0;
}
void PrintN(int m, int n)
{for (int i = (m <= n ? m : n)+1; i < (n >= m ? n : m); i++){if (narcissistic(i) == 1){printf("%d\n", i);}}
} 

二.編程題

7-1 尋找自守數

#include<stdio.h>
int ZISHOUnum(int p)
{int num = 0, count = 0;num = p * p;while (p != 0){if (p % 10 != num % 10)return 0;p /= 10;num /= 10;}return 1;
}int main()
{int n = 0, m = 0;int count = 0;scanf("%d %d", &n, &m);for (int i = n; i <= m; i++){if (ZISHOUnum(i)){count++;printf("%d\n", i);}}if (count == 0){printf("None\n");}return 0;
}