#include <stdio.h> #include <stdlib.h>  #define MAXSIZE 20 char *String_Create();         //創建串 int String_Length(char *s);       //求串長 void String_Show(char *s);       //輸出串 char *String_Copy(char *d, char *s);  //串復制 char *String_Connect(char *d, char *s); //串連接 char *String_SubStr(char *d, char *s, int pos, int len);  //求子串 int String_Compare(char *d, char *s);  //串比較 char *String_Insert(char *d, char *s, int pos);   //串插入 char *String_Delete(char *d, int pos, int len);   //串刪除 int String_Index(char *d, char *s, int pos);    //串匹配  int main(void) {   int choice;   char *str, *c;   int ans, pos, len;    c = (char*)malloc(sizeof(MAXSIZE));   printf("請輸入一串字符串(小于10個字符):/n");   str = String_Create();      while(1)   {     printf("***************************/n");     printf("字符串操作練習:/n");     printf("1.求串長/n");     printf("2.串復制/n");     printf("3.串連接/n");     printf("4.求子串/n");     printf("5.比較串/n");     printf("6.串插入/n");     printf("7.串刪除/n");     printf("8.串定位/n");     printf("9.串輸出/n");     printf("10.退出程序/n");          printf("輸入選擇:/n");     scanf("%d", &choice);     getchar();      switch(choice)     {     case 1:       ans = String_Length(str);       printf("串的長度為%d/n", ans);       break;     case 2:       c = String_Copy(c, str);       printf("目標字符串為:/n");       String_Show(c);       break;     case 3:       printf("輸入字串(小于10個字符)/n");       gets(c);       c = String_Connect(c, str);       printf("新的字符串為/n");       String_Show(c);       break;     case 4:       printf("輸入你想求子串所在位置及長度/n");       scanf("%d %d", &pos, &len);       c = String_SubStr(c, str, pos, len);       if(c == NULL)         printf("求子串失?。?n");       else       {         printf("所求子串為:/n");         String_Show(c);       }       break;     case 5:       printf("輸入字串:/n");       gets(c);       ans = String_Compare(c, str);       if(ans>0)         printf("首字符串大/n");       else if(ans<0)         printf("第二個字符串大/n");       else         printf("兩字符串相等/n");       break;     case 6:       printf("輸入需在主串中插入的字串/n");       gets(c);       printf("輸入插入的位置:/n");       scanf("%d", &pos);       str = String_Insert(str, c, pos);       printf("新的字符串為:/n");       String_Show(str);       break;     case 7:       printf("輸入刪除子串的起始位置及長度/n");       scanf("%d %d", &pos, &len);       str = String_Delete(str, pos, len);       break;     case 8:       printf("輸入要定位的子串:/n");       gets(c);       ans = String_Index(str, c, 1);       printf("定位的結果為%d/n", ans);       break;     case 9:       String_Show(str);       break;     case 10:       return 0;       break;     default:       printf("選擇無效!/n");       break;     }   }   return 1; }  //創建串 char *String_Create() {   char *s, ch;   int i = 0;    s = (char*)malloc(MAXSIZE);   ch = getchar();   while(ch != '#')   {     *(s+i) = ch;     i++;     ch = getchar();   }   if(i > MAXSIZE/2)     printf("輸入長度大于10!/n");   else     *(s+i) = '/0';   return s; }  //求串長 int String_Length(char *s) {   int l=0;    while(*s != '/0')   {     l++;     s++;   }    return l; }  //串的復制 char *String_Copy(char *d, char *s) {   char *c;    c = d;   while((*d++=*s++)!='/0');    return c; }  //串連接 char *String_Connect(char *d, char *s) {   char *c;   int l, i=0;;    c = d;   l = String_Length(d);   d = d + l;   while((*d++ = *s++) != '/0');    //串連接    return c; }  //求子串 char *String_SubStr(char *d, char *s, int pos, int len) {   char *c1, *c2=NULL;   int l, i;      c2 = (char*)malloc(MAXSIZE/2);    c1 = s;   d = c2;   l = String_Length(s);    if(pos>l || pos<1)      //輸入位置非法     return NULL;   if(len<0)          //輸入長度非法     return NULL;   c1 = c1 + pos - 1;      for(i=1; i<=len && *c1 != '/0'; i++) //求字串   {     *c2++ = *c1++;   }   *c2 = '/0';         //不要忘記結尾符號      return d; }  //串比較 int String_Compare(char *d, char *s) {   char *c1, *c2;    c1 = d;   c2 = s;    while(*c1 != '/0' || *c2 != '/0')   {     if(*c1 > *c2)       return 1;     else if(*c1 < *c2)       return -1;     c1++;     c2++;   }   if(*c1 == '/0' && *c2 == '/0')   //兩個字符處都結束時，則兩字符串相等     return 0;   else if(*c2 == '/0')        //第二個字符串先結束，則第一個字符串大     return 1;   else     return -1; }  //插入串 char *String_Insert(char *d, char *s, int pos) {   int i, ld,ls;   char *c1, *c2;    c1 = d;   c2 = s;    ld = String_Length(d);   ls = String_Length(s);    for(i=ld; i>=pos-1; i--)   //字符串后移，留出待插字符串位置     *(c1 + ls + i) = *(c1 + i);    for(i=pos; i<=pos+ls-1; i++) //插入子字符串     *(c1 + i - 1) = *c2++;   *(c1 + ld + ls) = '/0';     //最后的結尾符號不能忘掉    return d; }  //串刪除 char *String_Delete(char *d, int pos, int len) {   int i, l;    l = String_Length(d);   if(pos + len > l)        //如果刪除長度大于字串開始位置后面的長度，則只保留主串前面字符     *(d + pos -1) = '/0';   else   {     for(i=pos+len-1; i<=l; i++)       *(d + i - len) = *(d + i);     *(d + l - len) = '/0';   //結束字符   }    return d; }  //子串定位 int String_Index(char *d, char *s, int pos) {   int i = pos - 1, j = 0, ld, ls, b=0;    ld = String_Length(d);   ls = String_Length(s);   while(i < ld && j<ls)   {     if(*(d+i) == *(s+j))  //當前字符相等，則繼續匹配     {       i++;       j++;     }     else          //下一趟匹配     {       i = i - j + 1;       j = 0;     }   }   if(j == ls)     //匹配成功     return (i - ls + 1);   else     return 0; }  //輸出串 void String_Show(char *s) {   while(putchar(*s++));   printf("/n"); }