C语言用后序求表达式的结果

系统管理员 2022-08-09 02:12 127阅读 0赞

#include<stdio.h>
    #include<stdlib.h>
    #include<string.h>
    #include<malloc.h>
    # define MaxSize 50
    #define chartonumber(x) (x-'0')
    #define numbertochar(x) (x+'0')
    double op;
    
    
    typedef struct SqStack{
    	double data[MaxSize];
    	int top;
    }SqStack;
    
    void InitStack(SqStack &S){
    	S.top=-1;
    }
    
    bool StackEmpty(SqStack S){
    	if(S.top==-1)return true;
    	else return false;
    }
    
    bool Push(SqStack &S,double x){
    	if(S.top==MaxSize-1)return false;
    	else
    	S.data[++S.top]=x;
    	return true;
    }
    
    bool Pop(SqStack &S,double &x){
    	if(S.top==-1)return false;
    	x=S.data[S.top--];
    	return true;
    }
    
    bool GetTop(SqStack S,double &x){
    	if(S.top==-1)return false;
    	x=S.data[S.top];
    	return true;
    }
    
    
    typedef struct LinkNode{
    	double data;
    	int flag;
    	struct LinkNode *next;
    }LinkNode;
    
    typedef struct LinkQueue{
    	LinkNode *front,*rear;
    }LinkQueue;
    
    void InitQueue(LinkQueue &Q){
    	Q.front=Q.rear=(LinkNode*)malloc(sizeof(LinkNode));
    	Q.front->next=NULL;
    }
    
    bool IsEmpty(LinkQueue Q){
    	if(Q.front==Q.rear)return true;
    	else return false;
    }
    
    
    void EnQueue(LinkQueue &Q,double x,int y){
    	LinkNode *s;
    	s=(LinkNode*)malloc(sizeof(LinkNode));
    	s->data=x;
    	s->flag=y;
    	s->next=NULL;
    	Q.rear->next=s;
    	Q.rear=s;
    }
    
    bool DeQueue(LinkQueue &Q,double &x,int &y){
    	if(Q.front==Q.rear)return false;
    	LinkNode *p;
    	p=Q.front->next;
    	x=p->data;
    	y=p->flag;
    	Q.front->next=p->next;
    	if(Q.rear==p)Q.rear=Q.front;
    	free(p);
    	return true;
    }
    
    void calculate(LinkQueue Q){
    	SqStack S;
    	InitStack(S);
    	double num=0.0,arg=0.0;;int flag=0;double fx;int fy;
    	while(DeQueue(Q,fx,fy)){
    		if(fy==0){
    			if(flag==0){num=fx;flag=1;}
    			else if(flag==1){arg=fx;flag=2;}
    			else if(flag==2){
    				Push(S,num);
    				num=arg;
    				arg=fx;
    				flag=2;
    			}
    		}
    		else
    		if(fy==1){
    			if(flag==1){
    				arg=num;
    				Pop(S,num);
    				flag==2;
    			}
    				switch((int)fx){
    				case '+':num+=arg;flag=1;break;
    				case '-':num-=arg;flag=1;break;
    				case '*':num*=arg;flag=1;break;
    				case '/':num/=arg;flag=1;break;
    				default:printf("%s","请重新输入计算式");break;
    			}
    		}
    	}
    	printf("%.3f\n",num);
    }
    
    
    LinkQueue midtoend(char string[],int length){
    	LinkQueue Q;SqStack S;
    	InitQueue(Q);InitStack(S);
    	char c;
    	for(int i=0;i<length;i++){
    		double num=0.0;
    		c=string[i];
    		int numflag=chartonumber(c);
    		if(numflag>=0 && numflag<=9){
    			while((numflag>=0 && numflag<=9)){
    				num=num*10+numflag;
    				c=string[++i];
    				if(c=='.'){
    					c=string[++i];
    					numflag=chartonumber(c);int point=1;
    					while((numflag>=0 && numflag<=9)){
    						double dn=numflag;
    						while(point--){
    							dn=dn/10;
    						}
    						num+=dn;
    						point++;
    					}
    				}else
    				numflag=chartonumber(c);
    			}
    			EnQueue(Q,num,0);
    		}
    			switch(c){
    				case '(':
    						Push(S,'(');
    						break;
    				case '=':
    						while(Pop(S,op)){
    							EnQueue(Q,op,1);
    						}
    						break;
    				case ')':
    						Pop(S,op);
    						while(((int)op)!='('){
    							EnQueue(Q,op,1);;
    							Pop(S,op);
    						}
    						break;
    				case '+':
    						while(GetTop(S,op)){
    							if(((int)op)!='('){Pop(S,op);EnQueue(Q,op,1);}else break;
    						}
    						Push(S,'+');
    						break;
    				case '-':
    						while(GetTop(S,op)){
    							if(((int)op)!='('){Pop(S,op);EnQueue(Q,op,1);}else break;
    						}
    						Push(S,'-');
    						break;
    				case '*':
    						while(GetTop(S,op)){
    							if(((int)op)=='*'||((int)op)=='/'){Pop(S,op);EnQueue(Q,op,1);}else break;
    						}
    						Push(S,'*');
    						break;
    				case '/':
    						if(GetTop(S,op)){
    							if(((int)op)=='*'||((int)op)=='/'){Pop(S,op);EnQueue(Q,op,1);}
    						}
    						Push(S,'/');
    						break;
    				default : printf("%s","不是正确的表达式"); break; 
    			}
    	}
    	return Q;
    }
    
    
    int main(){
    	while(true){
    		char string[100];
    		int i=0;
    		gets(string);
    		while(string[i]!='\0'){
    			i++;
    		}
    		string[i++]='=';
    		int length=i;
    		calculate(midtoend(string,length));
    	}
    	return 0;
    }

</pre><pre name="code" class="plain">可以计算double型