#include <stdio.h>

//仔細(xì)分析有代表性的實(shí)例,發(fā)現(xiàn)規(guī)律.

typedef struct node????????// 結(jié)點(diǎn)類型定義????
{????
??float data;????
??bool sign;
????????struct node *lchild;????
????????struct node *rchild;????
}BTNode;????

BTNode *create(char *str,int n)????????// 創(chuàng)建代數(shù)表達(dá)式對(duì)應(yīng)的二叉樹????
{????
??BTNode *root = NULL;???? //始終指向當(dāng)前已經(jīng)生成的二叉樹的根
????????BTNode *p = NULL;???????????? //始終指向當(dāng)前待處理結(jié)點(diǎn)
????????float ch;????
????????int j = 0;????
????????ch = str[j];????
??while(ch != '\0' && j < n)????
??{????
????if(ch == '0' || ch == '1' ||ch == '2' ||ch == '3'||ch == '4' ||
??????ch == '5' || ch == '6' || ch == '7' || ch == '8'|| ch == '9')????
????{????
????????
??????p = new BTNode;????
????????????????????????p->data = ch;????
????????????????????????p->sign = false;
??????if(root == NULL)????????
????????root = p;????
??????else if(root->rchild == NULL)????????
????????root->rchild = p;????
??????else????????
????????root->rchild->rchild=p;????????
????}

????????else if(ch == '+' || ch == '-')
????????{
??????p = new BTNode;????
??????p->data = ch;????
??????p->sign = true;
??????p->rchild = NULL;????
??????p->lchild = root;????
??????root = p;????
??????root->rchild = NULL;????
????????}
????????else if(ch == '*' || ch == '/')
????????{
??????if(root->data >= '0' && root->data <= '9' || root->data == '*' || root->data == '/')????
??????{????????
????????p=new BTNode;????
????????p->data = ch;????
????????p->sign = true;
????????p->rchild = NULL;????
????????p->lchild = root;????
????????root = p;????
??????}????
??????else????
??????{????
????????p = new BTNode;????
????????p->data = ch;????
????????p->sign = true;
????????p->lchild = root->rchild;????
????????root->rchild = p;????
????????p->rchild = NULL;????
??????}????
????????}????
????????j++;????
????????ch=str[j];????
??}????
??return root;????
}????
float result(BTNode *b) //計(jì)算表達(dá)式????
{????
????float n1,n2;????
????if(b->data >= '0' && b->data <= '9')????
????????return (b->data - '0');????

????n1 = result(b->lchild);//計(jì)算左子表達(dá)式
????n2 = result(b->rchild);//計(jì)算右子表達(dá)式????
????
????if (b->sign == true && b->data == '+')
???? b->data = n1 + n2;
????else if (b->sign == true && b->data == '-')
???? b->data = n1 - n2;????
????else if (b->sign == true && b->data == '*')
???? b->data = n1 * n2;????????
????else if (b->sign == true && b->data == '/')
???? b->data = n1 / n2;

????return b->data;????
}????
void main()????
{????
??while(true)
??{
????BTNode static *b=NULL,*q=NULL;????
????char str[100];
????printf("請輸入符合要求的代數(shù)表達(dá)式：");????
????scanf("%s",str);????
????int n=0,i=0;????
????while(str[i++] != '\0')????
??????n++;????
????b = create(str,n);????
????printf("該表達(dá)式的值為：%f\n", result(b));????
??}

}

轉(zhuǎn)載于:https://blog.51cto.com/howin45/315936

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