串是字符串的簡稱。它是一種在數據元素的組成上具有一定約束條件的線性表，即要求組成線性表的所有數據元素都是字符，所以，人們經常這樣定義串：串是一個有窮字符序列。如： abcdef

串的長度為6

串中沒有任何字符，其串的長度為0，通常稱為空串。由空格字符組成的串，一班稱為空格串。串中任意連續的字符組成的子序列稱為該串的子串。包含子串的串又稱為該子串的主串。子串在主串中第一次出現的第一個字符的位置稱為子串在主串中的位置。兩個串的長度相等，并且各個對應的字符都相同，稱兩個串相等。串的存儲方式也分兩種：串的順序存儲結構和串的鏈式存儲結構

我寫的是一個堆分配存儲的串，代碼：

#include<iostream>#include<string>#include<malloc.h>using namespace std;//串的堆存儲方式typedef struct {	char *str;	int length;}HString;void init(HString  *s) {	s->length = 0;	s->str = NULL;}//串初始化void HStringInit(HString *s) {	char c;	int length;	cout << "請輸入串的長度：" << endl;	cin >> length;	s->length = length;	s->str = (char*)malloc((length+1)*sizeof(char));	for (int i = 0; i < s->length; i++) {		cin >> c;		s->str[i] = c;	}	cout << "初始化成功！" << endl;}//串賦值void HStringAssign(HString *s, HString *t) {				if (s->str) free(s->str);	int len = t->length;	s->length = len;	if (!len) {		s->str = (char*)malloc(sizeof(char));		s->str[0] = '/0';	}	else {		s->str = (char*)malloc(sizeof(char));		for (int i = 0; i < t->length; i++) {			s->str[i] = t->str[i];		}	}	cout << "賦值成功！" << endl;}//輸出串內容void PRint(HString *s) {								if (s->length == 0 && s->str == NULL) {		cout << "串的內容為空！" << endl;	}	else {		cout << "串的內容為：	";		for (int i = 0; i < s->length; i++) {			cout << s->str[i];		}		cout << endl;	}}//求串長void HStringLength(HString *s ) {						cout << "串的長度為：		" << s->length << endl;}//判串相等void HStringCompar(HString *s,HString *t) {					int flag = 0;	if (s->length != t->length) {		cout << "不相等！" << endl;	}	else {		if (s->length == 0) {			cout << "相等！" << endl;		}		else {			for (int i = 0; i < s->length&&i < t->length; i++) {				if (s->str[i] != t->str[i]) {					cout << "不相等！" << endl;					flag = 1;					break;				}			}			if (flag == 0) {				cout << "相等！" << endl;			}		}	}}//串連接void HStringConCat(HString *s,HString *t) {					HString s1;	init(&s1);	int i = 0;	HStringAssign(&s1, s);	s->length += t->length;	free(s->str);	s->str = (char*)malloc((s->length+1)*sizeof(char));	for (; i < s1.length; i++) {		s->str[i] = s1.str[i];	}	for (; i < s->length;i++) {		s->str[i] = t->str[i - s1.length];	}	free(s1.str);	free(t->str);	t->str = NULL;	t->length = 0;	cout << "連接完成！" << endl;}//求子串void HStringSub(HString *s,int start,int end) {				cout << "子串為：";	for (int i = start - 1; i < end; i++) {		cout << s->str[i];	}	cout << endl;}//子串定位void HStringIndex(HString *s,HString *t) {					int i = 0,j = 0;	while (i < s->length &&j < t->length) {		if (s->str[i] == t->str[j]) {			i++; 			j++;		}		else {			i = i - j + 1;			j = 0;		}	 }	if (j == t->length) {		cout << "子串的位置為:" << i-t->length + 1 << endl;	}	else {		cout << "沒有該子串！" << endl;	}}//串置換void HStringReplace(HString *s,HString *t) {			HString s1;	init(&s1);	HStringAssign(&s1, s);	HStringAssign(s, t);	HStringAssign(t, &s1);	free(s1.str);	s1.length = 0;	s1.str = NULL;	cout << "置換成功！" << endl;}//插入子串void HStringInsert(HString *s,int start,HString *t) {		HString s1;	init(&s1);	int i = 0,j;	HStringAssign(&s1, s);	s->length += t->length;	free(s->str);	s->str = (char*)malloc((s->length + 1) * sizeof(char));	for (; i < start-1; i++) {		s->str[i] = s1.str[i];	}	j = i;	for (int k = 0; k < t->length; k++, i++) {		s->str[i] = t->str[k];	}	for (; i < s->length; i++, j++) {		s->str[i] = s1.str[j];	}	cout << "插入成功！" << endl;}//刪除子串void HStringDelet(HString *s,int start,int length) {		int i = start,flag,k=length;	char c;	while (length != 0) {		s->str[i - 1] = 0;		length--;		i++;	}	for (int m = 0; m < s->length;m++) {		if (s->str[m] != 0 && s->str[m - 1] == 0) {			flag = m;			while (flag) {				if (s->str[flag - 1] != 0) {					break;				}				c = s->str[flag - 1];				s->str[flag - 1] = s->str[flag];				s->str[flag] = c;				flag--;			}		}	}	s->length -=k;	cout << "刪除成功！" << endl;}void message() {	cout << "************************************************************" << endl;	cout << "*	1  	輸出串          	2	串賦值	   *" << endl;	cout << "*	3	判串相等		4	求串長	   *" << endl;	cout << "*	5	串連接			6	求子串	   *" << endl;	cout << "*	7	子串定位		8	串置換	   *" << endl;	cout << "*	9	插入子串		10	刪除子串   *" << endl;	cout << "*	11	清屏			12	退出	   *" << endl;	cout << "************************************************************" << endl;}void main() {	int temp = 0,length;	HString S1, S2;	message();	cout << "對串S1進行初始化：" << endl;	HStringInit(&S1);	cout << "對串S2進行初始化：" << endl;	HStringInit(&S2);	int i = 0;	while (1) {				cin >> i;		switch (i) {		case 1:cout << "請輸入你要輸出的串    1:  S1,    2:   S2" << endl;										cin >> temp;					switch (temp) {							case 1:print(&S1); break;							case 2:print(&S2); break;							default:cout << "輸入錯誤！" << endl; break;					}				break;		case 2:	cout << "將S2賦值給S1" << endl;					HStringAssign(&S1, &S2);				break;		case 3:cout << "判斷S1和S2是否相等？" << endl;					HStringCompar(&S1, &S2);				break;		case 4:cout << "請輸入你要求的串    1:  S1,    2:   S2" << endl;					cin >> temp;					switch (temp) {							case 1:HStringLength(&S1); break;							case 2:HStringLength(&S2); break;							default:cout << "輸入錯誤！" << endl; break;					}				break;		case 5:cout << "將串S2連接到S1上！" << endl;					HStringConCat(&S1, &S2);				break;		case 6:cout << "求S1的子串：" << endl;				cout << "請輸入開始位置和長度：" << endl;				cin >> temp >> length;				if (temp > S1.length) {					cout << "輸出位置錯誤！" << endl;					break;				}				else {					if ((length - temp) > S1.length) {						cout << "子串長度超出！" << endl;					}					else {						HStringSub(&S1, temp, length);					}				}				break;		case 7:cout << "子串S2在S1中的位置" << endl;			HStringIndex(&S1,&S2);			break;		case 8:cout << "將S1和S2置換！" << endl;				HStringReplace(&S1,&S2);			break;		case 9:cout << "將S2插入到S1中" << endl;				cout << "請輸入插入位置：" << endl;				cin >> temp;				if (temp >= S1.length) {					cout << "插入位置錯誤！" << endl;					break;				}				else {					HStringInsert(&S1,temp,&S2);				}			break;		case 10:cout << "刪除S1的子串：" << endl;				cout << "請輸入開始位置和長度：" << endl;				cin >> temp >> length;				if (temp > S1.length) {					cout << "輸出位置錯誤！" << endl;					break;				}				else {					if ((length + temp) > S1.length+1) {					cout << "子串長度超出！" << endl;					}					else {						HStringDelet(&S1, temp, length);					}				}break;		case 11:system("cls"); message(); break;		case 12:exit(0); break;		default:cout << "輸入錯誤！請重新輸入：" << endl; break;		}	}}