(5)求子串运算 substring(s,i, len) linkstring substring (linkstring S, int i, int len) i int k; linkstring p, q,r,t; p=S,k=l; /用p查找S中的第个字符*/ while(p &&k<i)p= p->next; k++i if (p)printf("errol\n"); return(null);) else r=(linkstring) malloc(sizeof (linkstrnode) r->data=p->data; r->next=null,（5）求子串运算substring(S,i,len) linkstring substring(linkstring S,int i, int len) { int k; linkstring p,q,r,t; p=S, k=1; /*用p查找S中的第i个字符*/ while (p && k<i) {p= p->next;k++;} if (!p) {printf("error1\n"); return(null);} else { r=(linkstring) malloc (sizeof(linkstrnode)); r->data=p->data; r->next=null;