栈的应用---用栈计算逆波兰表达式

#include<stdio.h>

#include<stdlib.h>

struct Node;

typedef struct Node *PtrToNode;

typedef PtrToNode Stack;



struct Node{

    int Ele;

    PtrToNode Next;

};



Stack

CreateStack( void )

{

    Stack S;

    S = malloc( sizeof( struct Node ) );

    if(S == NULL )

        printf("out of space");

    S->Next = NULL;

    return S;

}

void

Push(int ch,Stack S)

{

    PtrToNode TmpCell;

    TmpCell = malloc(sizeof( struct Node ));

    if(TmpCell == NULL)

        printf("out of space ");

    else

    {

        TmpCell->Next = S->Next;

        S->Next = TmpCell;

        TmpCell->Ele = ch;

    }

}

int

IsEmpty(Stack S)

{

    return S->Next == NULL;

}

void

Pop( Stack S )

{

    PtrToNode TmpCell;

    TmpCell = S->Next;

    S->Next = TmpCell->Next;

    free(TmpCell);

}

int

Top( Stack S )

{

    return S->Next->Ele;

}



int main()

{

    char Tmp;

    int val1,val2,fin;

    Stack S;

    S = CreateStack();

    while( ( Tmp = getchar() ) != '\n' )

    {

        if(Tmp == ' ')

            continue;

        if(Tmp >= '0' && Tmp <= '9')

            Push( Tmp - '0',S );

        else if(Tmp == '+')

        {

            val1 = Top( S );

            Pop( S );

            val2 = Top( S );

            Pop( S );

            fin = val1 + val2;

            Push(fin, S );

        }

        else if( Tmp == '-' )

        {

            val1 = Top( S );

            Pop( S );

            val2 = Top( S );

            Pop( S );

            fin = val1 - val2;

            Push(fin, S );

        }

        else if( Tmp == '*' )

        {

            val1 = Top( S );

            Pop( S );

            val2 = Top( S );

            Pop( S );

            fin = val1 * val2;

            Push(fin, S );

        }

        else

        {

            val1 = Top( S );

            Pop( S );

            val2 = Top( S );

            Pop( S );

            fin = val1 / val2;

            Push(fin, S );

        }

    }

    printf("%d",Top( S ));

    return 0;

}

View Code

算法思想：遇到数字就进栈，遇到+ - * / 就出栈两个元素计算，再压入栈中