level1 2-5

P02_isprime.c

@@ -0,0 +1,34 @@
+#include<stdio.h>
+#include<stdlib.h>
+int IS(int);			//判断是否为素数
+int main() {
+	int x;
+	printf("输入一个正整数，程序判断它是否为素数（q to quit）:");
+	while (scanf_s("%d", &x))
+	{
+		if (x == 1 || x == 2) {
+			puts("是素数");
+		}
+		else if (IS(x))
+			puts("是素数.");
+		else puts("不是素数.");
+		printf("输入一个正整数，程序判断它是否为素数（q to quit）:");
+	}
+	system("pause");
+	return 0;
+}
+int IS(int x)
+{
+	int i;
+	int mark = 0;	//创建标记
+	for (i = 2; i < x; i++)
+	{
+		if (x%i == 0)
+		{
+			mark = 1;	//若被整除，标记mark为1
+			break;
+		}
+	}if (mark == 1)
+			return 0;
+		else return 1;
+}

p03_Diophantus.c

@@ -0,0 +1,14 @@
+#include<stdio.h>
+#include<stdlib.h>
+
+void main()
+{
+	int i;
+	for (i = 1; 28 * i != 21 * i + 4 * i + 252; i++)
+	{
+		;
+	}
+	printf("丢番图的年纪是%d\n", i);
+	system("pause");
+}
+

p04_ narcissus.c

@@ -0,0 +1,19 @@
+#include<stdio.h>
+#include<stdlib.h>
+int main()
+{
+	int a, b, c;
+	for (a = 0; a <= 9; a++)
+	{
+		for (b = 0; b <= 9; b++)
+		{
+			for (c = 0; c <= 9; c++)
+			{
+				if (a*a*a + b*b*b + c*c*c == a + 10 * b + 100 * c && !( b == 0 && c == 0))		//排除非三位数（0开头）的情况
+				printf("%d%d%d\n", c, b, a);
+			}
+		}
+	}
+	system("pause");
+	return 0;
+}

p05_allPrimes.c

@@ -0,0 +1,35 @@
+#include<stdio.h>
+#include<stdlib.h>
+#include<time.h>
+int isprinme(int a);
+int IS(int);
+int main()
+{
+	clock_t t1, t2;
+	t1 = clock();
+	for(int i=2;i<=1000;i++)
+	{
+		if (isprinme(i))
+			printf("%5d", i);
+	}
+	t2 = clock();
+	printf("打印时间:%f秒",(double)(t2-t1)/CLOCKS_PER_SEC);
+	system("pause");
+	return 0;
+}
+int isprinme(int a) 
+{
+	int mark = 0;
+	for (int i = 2; i < a; i++)
+	{
+		if (a%i == 0)	//用mark标记a已被整除
+		{
+			mark = 1;
+			break;
+		}
+
+	}
+	if (mark == 1)		//检查标记
+		return 0;
+	else return 1;
+}

p06_Goldbach.c

@@ -0,0 +1,54 @@
+#include<stdio.h>
+#include<stdlib.h>
+#include<string.h>
+int loadPrime(int* a);
+int isPrime(int x);
+int main()
+{
+	int prime[100] = {0};
+	int sum;
+	int a = 4;
+	sum=loadPrime(prime);
+	for (int i = 0; i < sum; i++)
+	{
+		for (int j = 0; j < sum; j++)
+		{
+			if (a == prime[i] + prime[j])		//遍历两个100以内的素数组合之和，与a作比较
+			{
+				printf("%3d满足哥德巴赫猜想\n", a);
+				a += 2;							//判断下一个偶数
+			}
+
+		}
+	}
+	system("pause");
+	return 0;
+}
+int isPrime(int x)
+{
+	int i;
+	int mark = 0;	//创建标记
+	for (i = 2; i < x; i++)
+	{
+		if (x%i == 0)
+		{
+			mark = 1;	//若被整除，标记mark为1
+			break;
+		}
+	}if (mark == 1)
+		return 0;
+	else return 1;
+}
+int loadPrime(int* a)
+{	
+	int x = 0;		
+	for (int i = 2; i < 100; i++)
+	{
+		if (isPrime(i))
+		{
+			a[x] = i;	//把素数赋值给数组
+			x++;
+		}
+	}
+	return x;		//返回100以内的素数个数
+}