diff --git a/assignment/C/lixinyi/work1 b/assignment/C/lixinyi/work1
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+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+#include <assert.h>
+// assert(x)的作用是，如果x为假，则报错并终止程序运行
+
+// 返回n的降k阶乘：n*(n-1)*(n-2)*...*(n-k+1)
+int falling(int n, int k)
+{
+	int result =1;
+	for(int i=0;i<k;i++){
+		result*=n;
+		n--;
+	} 
+	return result;
+}
+void check1()
+{
+	assert(falling(5, 3) == 60);
+	assert(falling(5, 5) == 120);
+	assert(falling(5, 0) == 1);
+}
+
+// 判断n是否为素数，是素数返回1，否则返回0
+int isPrime(int n)
+{
+	if(n<=1)
+	 return 0;
+	for (int i=2;i<=sqrt(n);i++){
+		if(n%i==0){
+			return 0;
+		}
+	}
+	return 1;
+}
+void check2()
+{
+	assert(isPrime(2) == 1);
+	assert(isPrime(4) == 0);
+	assert(isPrime(25) == 0);
+	assert(isPrime(31) == 1);
+	assert(isPrime(91) == 0);
+	assert(isPrime(97) == 1);
+}
+
+// 矩阵乘，将A*B的结果存入C中，A、B、C均为3*3的二维数组
+void matrixMul(int A[3][3], int B[3][3], int C[3][3])
+{
+	for (int i=0;i<3;i++){
+		for(int j=0;j<3;j++){
+			C[i][j]=0;
+			for(int k=0;k<3;k++){
+				C[i][j]+=A[i][k]*B[k][j];
+			}
+		}
+	}
+}
+
+void check3()
+{
+	int A[3][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
+	int B[3][3] = {{10, 12, 14}, {16, 18, 20}, {22, 24, 26}};
+	int C[3][3]; // 注意：C中的元素未初始化
+	int D[3][3] = {{108, 120, 132}, {252, 282, 312}, {396, 444, 492}};// A*B的正确结果
+	matrixMul(A, B, C);
+	for (int i = 0; i < 3; i++)
+		for (int j = 0; j < 3; ++j)
+			assert(C[i][j] == D[i][j]);
+}
+
+
+
+// 扩展欧几里得算法，计算a*x+b*y=gcd(a,b)的一组解
+// 返回gcd(a,b)，将x、y的值通过指针参数返回
+int exgcd(int a, int b, int *x, int *y)
+{
+	if(b==0){
+		*x=1;
+		*y=0;
+		return a;
+	}
+	int x1,y1;
+	int gcd=exgcd(b,a%b,&x1,&y1);
+	*x=y1;
+	*y=x1-(a/b)*y1;
+	return gcd;
+}
+
+void check4()
+{
+	int x, y;
+	assert(exgcd(3, 5, &x, &y) == 1);
+	assert(x == 2);
+	assert(y == -1);
+	assert(exgcd(4, 6, &x, &y) == 2);
+	assert(x == -1);
+	assert(y == 1);
+}
+
+int main()
+{
+	// 测试代码，可以先一个一个写，然后逐个check
+	check1();
+	check2();
+	check3();
+	check4();
+	puts("Tests passed!");
+	return 0;
+}
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