diff --git a/8.c b/8.c
new file mode 100644
index 0000000..c7bfe78
--- /dev/null
+++ b/8.c
@@ -0,0 +1,245 @@
+#include <stdio.h>
+#include <string.h>
+
+struct Data
+{
+	int ID;
+	int Class;
+	float score1;
+	float score2;
+	float score3;
+	char name[101];
+} stu[1001];
+int stl = 0;
+struct Data* stuflag = 0;
+
+float total(struct Data* a) {
+	return a->score1 + a->score2 + a->score3;
+}
+
+void swap(struct Data* a, struct Data* b) {
+	struct Data t = *a;
+	*a = *b;
+	*b = t;
+
+	if (a == stuflag) stuflag = b;
+else 
+	if (b == stuflag) stuflag = a;
+}
+
+void Sort() {
+	int i, j;
+	for(i = 0; i < stl-1; i++) {
+		for (j = 0; j < stl-i-1; j++) {
+			if (stu[j].Class < stu[j+1].Class) continue;
+			if (stu[j].Class > stu[j+1].Class || 
+			total(&stu[j]) < total(&stu[j+1])) swap(&stu[j], &stu[j+1]);
+		}
+	}
+}
+
+void input1() {
+	scanf("%d", &stu[stl].ID);
+	scanf("%f", &stu[stl].score1);
+	scanf("%f", &stu[stl].score2);
+	scanf("%f", &stu[stl].score3);
+	stl++;
+}
+
+
+void Input() {
+	printf("Please input info of three students:\n");
+	input1();input1();input1();
+	if (total(&stu[stl-3]) < total(&stu[stl-2])) swap(&stu[stl-3], &stu[stl-2]);
+	if (total(&stu[stl-2]) < total(&stu[stl-1])) swap(&stu[stl-2], &stu[stl-1]);
+	if (total(&stu[stl-3]) < total(&stu[stl-2])) swap(&stu[stl-3], &stu[stl-2]);
+	printf("%d,%.1f,%.1f\n", stu[stl-3].ID, total(&stu[stl-3]), total(&stu[stl-3])/3.0f);
+	printf("%d,%.1f,%.1f\n", stu[stl-2].ID, total(&stu[stl-2]), total(&stu[stl-2])/3.0f);
+	printf("%d,%.1f,%.1f\n", stu[stl-1].ID, total(&stu[stl-1]), total(&stu[stl-1])/3.0f);
+}
+
+void Print1(int i)
+{
+	printf("%d,%d,%s,%.1f,%.1f,%.1f,%.1f\n", stu[i].ID, stu[i].Class, stu[i].name,
+				 stu[i].score1, stu[i].score2, stu[i].score3, total(&stu[i]));
+}
+
+void Search() {
+	int t; char com[101]; 
+	int i;
+	scanf("%d %s", &t, com);
+	switch(t) {
+		case 1: {
+			int from, to;
+			sscanf(com, "%d-%d", &from, &to);
+			for (i=0; i<stl; i++) {
+				if (stu[i].Class >= from && stu[i].Class <= to)
+					Print1(i);
+			}
+		}break;
+		case 2: {
+			int from, to;
+			sscanf(com, "%d-%d", &from, &to);
+			for (i=0; i<stl; i++) {
+				if (stu[i].ID >= from && stu[i].ID <= to)
+					Print1(i);
+			}
+		}break;
+		case 3: {
+			for (i=0; i<stl; i++) {
+				int flag = 1, j;
+				for (j=0; com[j] != '*'; j++) {
+					if (stu[i].name[j] != com[j]) {
+						flag = 0; break;
+					}
+				}
+				if(flag)
+					Print1(i);
+			}
+		}break;
+		case 4: {
+			float gate;
+			sscanf(com, "%f", &gate);
+			for (i=0; i<stl; i++) {
+				if (total(stu + i) >= gate - 0.01f)
+					Print1(i);
+			}
+		}break;
+		case 5: {
+			int Class, from, to;
+			sscanf(com, "%d.%d-%d", &Class, &from, &to);
+			for (i=0; i<stl; i++) {
+				if (stu[i].ID >= from && stu[i].ID <= to)
+				if (stu[i].Class == Class)
+					Print1(i);
+			}
+		}
+	}
+}
+
+void Output() {
+	int i;
+	for(i=0; i<stl; i++) {
+		printf("%d,%d,%s,%.1f,%.1f,%.1f,%.1f\n", stu[i].ID, stu[i].Class, stu[i].name,
+			stu[i].score1, stu[i].score2, stu[i].score3, total(&stu[i]));
+	}
+}
+
+void Typein()
+{
+	printf("Id ");
+	scanf("%d", &stu[stl].ID);
+	printf("class ");
+	scanf("%d", &stu[stl].Class);
+	printf("name ");
+	scanf("%s", stu[stl].name);
+	printf("score1 ");
+	scanf("%f", &stu[stl].score1);
+	printf("score2 ");
+	scanf("%f", &stu[stl].score2);
+	printf("score3 ");
+	scanf("%f", &stu[stl].score3);
+	stl++;
+}
+
+void Delete() {
+	int ID = -1; char name[101];
+	scanf("%s", name);
+	getchar();
+	int NumFlag = 1, i;
+	for(i = 0; name[i]!='\0'; i++)
+		if (name[i] < '0' || name[i] > '9') {
+			NumFlag = 0; break;
+		}
+	if (NumFlag) {
+		sscanf(name, "%d", &ID);
+		name[0] = '\0';
+	}
+	for(i=0; i<stl; i++) {
+		if(stu[i].ID == ID || (name[0]!='\0' && strcmp(stu[i].name, name) == 0)) {
+			struct Data* r = stu + i;
+			for(; r+1 < stu+stl; r++) {
+				*r = *(r+1);
+			}
+			stl--;
+			break;
+		}
+	}
+	Output();
+}
+
+void Select_3() {
+	char com[101];
+	scanf("%s", com);
+	int NumFlag = 1, i;
+	for(i = 0; com[i]!='\0'; i++)
+		if (com[i] < '0' || com[i] > '9') {
+			NumFlag = 0; break;
+		}
+	if (NumFlag) {
+		int num;
+		sscanf(com, "%d", &num);
+		if (strlen(com) > 2) 
+			for (i=0; i<stl; i++) {
+				if (stu[i].Class == num)
+				Print1(i);
+			}
+		else 
+			for (i=0; i<stl; i++) 
+				if (stu[i].ID == num)
+				Print1(i);
+	}
+	else {
+		for (i=0; i<stl; i++) 
+			if (strcmp(stu[i].name, com) == 0)
+				Print1(i);
+	}
+}
+
+int main() {
+	char com[11];
+	while(1) {
+		printf("1.input\n");
+		printf("2.delete\n");
+		printf("3.select\n");
+		printf("4.order\n");
+		printf("5.output\n");
+		printf("6.quit\n");
+		printf("please input your option\n");
+		int t; scanf("%d", &t);
+		switch(t) {
+			case 1: 
+			do{
+				Typein();
+				printf("continue?\n");
+				scanf("%s", com);
+			}while(strcmp(com, "yes") == 0);
+			Sort();
+			break;
+			case 2:
+			do {
+				Delete();
+				printf("continue?\n");
+				scanf("%s", com);
+			}while(strcmp(com, "yes") == 0);
+			break;
+			case 3: 
+			do {
+				Select_3();
+				printf("continue?\n");
+				scanf("%s", com);
+			}while(strcmp(com, "yes") == 0);
+			break;
+			case 4:
+			Sort();
+			Output();
+			break;
+			case 5:
+			Output();
+			break;
+			case 6:
+			return 0;
+			break;
+		}
+	}
+}