表达式求值算法的实现
#include
#include
#define STACK_INIT_SIZE 100
#define STACKINCREMENT 10
typedef struct{
int *base;
int *top;
int stacksize;
}Sqstack1;
Sqstack1 opnd;
typedef struct{
char *base;
char *top;
int stacksize;
}Sqstack2;
Sqstack2 optr;
void Initstack_optr(){
optr.base=(char*)malloc(STACK_INIT_SIZE*sizeof(char));
if(!optr.base) exit(1);
optr.top=optr.base;
optr.stacksize=STACK_INIT_SIZE;
*optr.top++='#';
//printf("the first tergert is %c",*(optr.top-1));
}
void Initstack_opnd(){
opnd.base=(int*)malloc(STACK_INIT_SIZE*sizeof(int));
if(!opnd.base) exit(1);
opnd.top=opnd.base;
opnd.stacksize=STACK_INIT_SIZE;
}
int In(char c){
int n;
switch(c){
case'+':
case'-':
case'*':
case'/':
case'(':
case')':
case'[':
case']':
case'#': n=1;break;
default: n=0;break;
}
return n;
}
void pushopnd(int c){
if(opnd.top-opnd.base>=opnd.stacksize)
{
opnd.base=(int *)realloc(opnd.base,(opnd.stacksize+STACKINCREMENT)*sizeof(int));
if(!opnd.base) exit(1);
opnd.top=opnd.base+opnd.stacksize;
opnd.stacksize+=STACKINCREMENT;
}
*opnd.top++=c;
//printf("%d have been put into opndstack!/n",c);
}
void pushoptr(char c){
if(optr.top-optr.base>=optr.stacksize)
{optr.base=(char*)realloc(optr.base,(optr.stacksize+STACKINCREMENT)*sizeof(char));
if(!optr.base) exit(1);
optr.stacksize+=STACKINCREMENT;
}
*optr.top++=c;
//printf("%c have been put into optrstack!/n",c);
}
int Gettopopnd(){
if(opnd.top==opnd.base) exit(1);
return *(opnd.top-1);
}
int Gettopoptr(){
if(optr.top==optr.base) exit(1);
return *(optr.top-1);
}
int popopnd(){
if(opnd.top==opnd.base) exit(1);
return *--opnd.top;
}
int popoptr(){
if(optr.top==optr.base) exit(1);
return *--optr.top;
}
int operate(int a,char theta,int b){
int terminal;//printf("hello !");
switch (theta){
case '+': terminal=a+b;break;
case '-': terminal=a-b;break;
case '*': terminal=a*b;break;
case '/': terminal=a/b;break;
}
return terminal;
}
int Precede(char c1,char c2){
char result;
switch(c2){
case '#': if(c1=='#') result='=';
else
result='>';break;
case '+':
case '-':if(c1=='('||c1=='#') result='<';
else
result='>';break;
case '*':
case '/':
if(c1=='*'||c1=='/'||c1==')')
result='>';
else
result='<';break;
case '(': result='<';break;
case ')': if(c1=='(')
result='=';
else
result='>';break;
}
return result;
}
int main(){
char c,c1,theta;
int a,b,terminal,mid;
//int i=0,j;
//char c2;
Initstack_optr();
/*for(;i<=5;i++){
c=getchar();
pushoptr(c);
}
while (optr.base !=optr.top ){
c2=popoptr();
printf("%c",c2);
}*/
/*for(;i<=5;i++){
j=getchar();
pushopnd(j);
}
while (opnd.base !=opnd.top ){
j=popopnd();
printf("%d",j);
}*/
Initstack_opnd();
c=getchar();
while('#'!=c||('#'!=(Gettopoptr()))){
if(!(In(c))){
//int first;
pushopnd(int(c-48));
//first=Gettopopnd();
//printf("the top is %d",first);
c=getchar();
}
else
{
c1=Gettopoptr();
switch(Precede(c1,c)){
case '<': pushoptr(c);c=getchar();break;
case '=': popoptr();c=getchar();break;
case '>': theta=popoptr();a=popopnd();b=popopnd();
mid=operate(b,theta,a);
//printf("%d",mid);
pushopnd(mid);
if (c==')'){
popoptr();c=getchar();}
else if(c!='#'){ pushoptr(c);
c=getchar();}
else continue;break;
}
}
}
terminal=Gettopopnd();
printf("the terminal tergert is %d",terminal);
return 0;
}