实验3

`#define _CRT_SECURE_NO_WARNINGS

include <stdio.h>

char score_to_grade(int score);

int main() {
int score;
char grade;

while (scanf("%d", &score) != EOF) {
	grade = score_to_grade(score);
	printf("分数：%d,等级：%c\n\n", score, grade);
}
return 0;

}

char score_to_grade(int score) {
char ans;

switch (score / 10) {
case 10:
case 9:ans = 'A'; break;
case 8:ans = 'B'; break;
case 7:ans = 'C'; break;
case 6:ans = 'D'; break;
default:ans = 'E';
}

return ans;

}`

功能：将成绩按分数划分等级
参数类型：整形
返回值类型：字符型
问题：字符型常量应用单引号括起来，不应该用双引号

`#define _CRT_SECURE_NO_WARNINGS

include <stdio.h>

int sum_digits(int n);
int main() {
int n;
int ans;

while (printf("Enter n:"), scanf("%d", &n) != EOF) {
	ans = sum_digits(n);
	printf("n=%d,ans=%d\n\n", n, ans);
}
return 0;

}

int sum_digits(int n) {
int ans = 0;

while (n != 0) {
	ans += n % 10;
	n /= 10;
}

return ans;

}`

功能：计算这个数各位数之和
可以实现相同的结果，原来的算法是利用while循环语句进行计算，后面的算法是用递推，多次使用该函数进行计算。

`#define _CRT_SECURE_NO_WARNINGS

include<stdio.h>

int power(int x, int n);

int main() {
int x, n;
int ans;

while (printf("Enter x and n:"), scanf("%d%d", &x, &n) != EOF) {
	ans = power(x, n);
	printf("n=%d,ans=%d\n\n", n, ans);
}

return 0;

}

int power(int x, int n) {
int t;

if (n == 0)
	return 1;
else if (n % 2)
	return x * power(x, n - 1);
else {
	t = power(x, n / 2);
	return t * t;
}

}`

功能：计算x的n次幂
是递归，公式是x^n=x*x(n-1)

`#define _CRT_SECURE_NO_WARNINGS

include<stdio.h>

int is_prime(int n);
int main() {
int i, n, sum;
i == 1;
sum = 0;
scanf("%d", &n);
for (i = 1; i < n-1; ++i) {
if (i < 2) {
continue;
}
else {
is_prime(i);
}
if (is_prime(i) && is_prime(i + 2)) {
++sum;
printf("n以内的孪生素数：%d%d\n", i, i + 2);
}

}

printf("n以内的孪生素数总和：%d\n", sum);

return 0;

}

int is_prime(int n) {
if (n <= 1)
return 0;
else if (n == 2)
return 1;
else if (n % 2 == 0)
return 0;
int j;
for (j = 3; j * j <= n; j += 2) {
if (n % j == 0)
return 0;
}
return 1;

}`

`#define _CRT_SECURE_NO_WARNINGS

include<stdio.h>

int func(int n, int m);

int main() {
int n, m;
int ans;

while (scanf("%d%d", &n, &m) != EOF) {
	ans = func(n, m);
	printf("n=%d,m=%d,ans=%d\n\n", n, m, ans);
}
return 0;

}

int func(int n, int m) {
int a=1, b=1, c=1,res;

for (int i = 1 ; i <= n ; i++ ) {
	a = a * i;
}

for (int i = 1; i <= m;i++) {
	b = b*i;
}

int temp;
temp = n - m;
for (int i=1; i<=temp; i++) {
	c = c * i;
}
res = a / (b * c);
return res;

}

`

`#define _CRT_SECURE_NO_WARNINGS

include<stdio.h>

int gcd(int a,int b,int c);

int main() {
int a, b, c;
int ans;
while (scanf("%d%d%d", &a, &b, &c) != EOF) {
ans = gcd(a, b, c);
printf("最大公约数：%d\n\n", ans);
}

return 0;

}

int gcd(int a,int b,int c) {
int i,ans;
if (a > b && a > c) {
i = a;
}
else if (b > a && b > c) {
i = b;
}
else {
i = c;
}
for (int j = i; j>=1; --j) {
if (a % j == 0 && b % j == 0 && c % j == 0) {
ans = j;
break;
}

}
return ans;

}`

`#define _CRT_SECURE_NO_WARNINGS

include<stdio.h>

include<stdlib.h>

int print_charman(int n);
int main() {
int n;

printf("Enter n:");
scanf("%d", &n);
print_charman(n);

return 0;

}

int print_charman(int n) {

for (int i = n; i>= 1;--i) {
	// O 
	for (int j = 1; j <= n - i; j++) {
		printf("   \t");
	}
	for (int j = 1; j <= 2*i-1; j++)
	{
		printf(" O \t");
	}
	printf("\n");
	//<H>
	for (int j = 1; j <= n - i; j++) {
		printf("   \t");
	}
	for (int j = 1; j <= 2 * i - 1; j++)
	{
		printf("<H>\t");
	}
	printf("\n");
	//I I
	for (int j = 1; j <= n - i; j++) {
		printf("   \t");
	}
	for (int j = 1; j <= 2 * i - 1; j++)
	{
		printf("I I\t");
	}
	printf("\n");
	//\n
	printf("\n");
}

}`