C语言实现逆波兰式实例
代码如下:
#include<stdio.h>
#include<string.h>
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));
}
