栈5-后缀表达式求解

栈5-后缀表达式的求解

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求解过程

8 3 1 - 5 * +

数字:进栈 [1,3,8]

符号: -

从栈中弹出右操作数 -1

从栈中弹出左操作数 3-1

根据符号进行运算 2

将运算结果压入栈中 [2,8]

遍历结束, 栈中唯一的数字作为计算结果

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定义栈结构

typedef struct MYNUM{
    LinkNode node;
    int val;
} MyNum;

判断数字

int isNumber(char c){
    return c>='0' && c<='9';
}

运算符号操作

int operatorOperate(char c,int rightNum, int leftNum){
    if(c=='+') return leftNum+rightNum;
    if(c=='-') return leftNum-rightNum;
    if(c=='*') return leftNum*rightNum;
    if(c=='/') return leftNum/rightNum;
}

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测试

int main(){
    char *str = "831-5*+";
    char *p = str;
    //创建栈
    LinkStack *stack = Init_LinkStack();
    //'\0'是字符的末尾
    while(*p!='\0'){
        if(isNumber(*p)){
            MyNum *num = (MyNum*)malloc(sizeof(MyNum));
            num->val = *p-'0';
            Push_LinkStack(stack, (LinkNode*)num);
        }else{
            //弹出右操作数
            int rightNum = ((MyNum*)Top_LinkStack(stack))->val;
            Pop_LinkStack(stack);
            //弹出左操作数 
            int leftNum = ((MyNum*)Top_LinkStack(stack))->val;
            Pop_LinkStack(stack);
            //结果进栈
            MyNum *num = (MyNum*)malloc(sizeof(MyNum));
            num->val = operatorOperate(*p, rightNum, leftNum);
            Push_LinkStack(stack,(LinkNode*)num);
        }
        p++;   
    }

    if(Size_LinkStack(stack)==1){
        MyNum *num1 = (MyNum*)Top_LinkStack(stack);
        cout << str << "的结果是:" << num1->val << endl;
        Pop_LinkStack(stack);
    }

    //释放内存
    FreeSpace_LinkStack(stack);

    system("pause");
    return 0;
}