C语言实现逆波兰式实例

typedef struct{char s[20][20];int top;}SQ;

void copystr(char *a,char *b)
{
    int i=0;
    do
    {
        b[i]=a[i];
        i++;
    }
    while(a[i]!='\0');
    b[i]='\0';
}

void voidSQ(SQ *s)
{
    s->top=-1;
}

int ifempty(SQ *s)
{
    return(s->top==-1);
}

void push(SQ *S,char *c)
{
    if(S->top==19)
        printf("over flow\n");
    else
    {

        S->top++;
        copystr(c,S->s[S->top]);
    }
}
char *pop(SQ *S)
{
    if(ifempty(S))
    {
        printf("over flow!\n");
        return(NULL);
    }
    else
        return(S->s[S->top--]);
}

int judge(char *c)
{
    if(c[1]=='\0')
        switch(c[0])
    {
        case '+':return(3);
        case '-':return(3);
        case '*':return(2);
        case '/':return(2);
        default:return(1);
    }
    else
        return(1);
}

void write(char *a,char *b,char *c)
{
    strcat(a,c);
    strcat(a,b);
}

int seek(char *c,int start)
{
    int signal=1;
    for(start=start++;c[start]!='\0'&&signal!=0;start++)
    {
        if(c[start]==')')
            signal--;
        else if(c[start]=='(')
            signal++;
    }
    if(signal==0)
        return(start-1);
    else
    {
        printf("输入无效式子\n");
        return(-1);
    }
}
void FB(SQ *A,SQ *B)
{
    for(;!ifempty(A);)
    {
        push(B,A->s[A->top]);
        pop(A);
    }
}

char *rewrite(char *A)
{
    SQ front;
    SQ back;
    int i,j,k,flag=0;
    char *result;
    char mid[20];
    voidSQ(&front);
    voidSQ(&back);
    for(i=0;A[i]!='\0';)
    {
        if(A[i]=='(')
        {
            j=seek(A,i);
            for(k=i+1;k<j;k++)
            {
                mid[k-i-1]=A[k];
            }
            mid[j-i-1]='\0';
            copystr(rewrite(mid),mid);
            push(&back,mid);
            i=j+1;
        }
        else if(A[i]!='(')
        {
            mid[0]=A[i];
            mid[1]='\0';
            push(&back,mid);
            i++;
        }
    }
    FB(&back,&front);
    for(;front.top>=2;)
    {
        flag=0;
        for(i=0;i<=front.top;i++)
        {
            if(judge(front.s[i])==2)
            {
                flag=1;
                break;
            }

        }
        if(flag==1)
        {
            for(;front.top>=2;)
            {
                if(judge(front.s[front.top])==1&&judge(front.s[front.top-1])==2&&judge(front.s[front.top-2])==1)
                {
                    write(front.s[front.top],front.s[front.top-1],front.s[front.top-2]);
                    push(&back,front.s[front.top]);
                     pop(&front);
                    pop(&front);
                     pop(&front);
                }
                else
                {
                    push(&back,front.s[front.top]);
                    pop(&front);
                }
            }
            FB(&front,&back);
            FB(&back,&front);
        }
        else
        {
            for(;front.top>=2;)
            {
                if(judge(front.s[front.top])==1&&judge(front.s[front.top-1])==3&&judge(front.s[front.top-2])==1)
                {
                    write(front.s[front.top],front.s[front.top-1],front.s[front.top-2]);

                    push(&back,front.s[front.top]);
                     pop(&front);
                    pop(&front);
                     pop(&front);
                }
                else
                {
                    push(&back,front.s[front.top]);
                    pop(&front);
                }
            }
            FB(&front,&back);
            FB(&back,&front);
        }
    }
    result=front.s[front.top];
    return(result);
}

typedef struct{char c[20];int top;}sq;
int execute(char a,char b,char c)
{
    switch(a)
    {
    case('+'):return((c-48)+(b-48));
    case('-'):return((c-48)-(b-48));
    case('*'):return((c-48)*(b-48));
    case('/'):return((c-48)/(b-48));
    }
}

void voidsq(sq *s)
{
    s->top=-1;
}

int ifsqempty(sq *s)
{
    return(s->top==-1);
}

void pushsq(sq *s,char x)
{
    if(s->top==19)
        printf("over flow!\n");
    else
    {
        s->top=s->top+1;
        s->c[s->top]=x;
    }
}

void popsq(sq *s)
{
    if(ifsqempty(s))
        printf("over flow!\n");
    else
        s->top--;
}

int just(char c)
{   
    switch(c)
    {
        case ('+'):return(0);
        case ('-'):return(0);
        case ('*'):return(0);
        case ('/'):return(0);
        default:return(1);
    }
}

void restread(sq *a,sq *b)
{
    for(;!ifsqempty(a);)
    {
        pushsq(b,a->c[a->top]);
        popsq(a);
    }
}

int calculate(char *c)
{
    sq rest,read;
    int i,re;
    voidsq(&rest);
    voidsq(&read);
    for(i=0;c[i]!='\0';i++)
        pushsq(&read,c[i]);
    for(;read.top>=2;)
    {
        for(;read.top>=2;)
        {
            if(just(read.c[read.top])==0&&just(read.c[read.top-1])==1&&just(read.c[read.top-2]) ==1)
            {

                re=execute(read.c[read.top],read.c[read.top-1],read.c[read.top-2]);
                pushsq(&rest,re+48);
                popsq(&read);
                popsq(&read);
                 popsq(&read);
            }
            else
            {
                pushsq(&rest,read.c[read.top]);
                popsq(&read);
            }
        }
        restread(&read,&rest);
        restread(&rest,&read);
    }
    return(read.c[0]-48);
}

void main()
{
    char re[20];
    char a[20];
    printf("请输入算式：\n");
    scanf("%s",a);
    copystr(rewrite(a),re);
    printf("逆波兰式：\n%s\n",re);
    printf("求值结果：\n%d\n",calculate(re));

}