表达式C++_C++_源码

#define NULL 0 #include<string.h> #include<stdio.h> #include"stdlib.h" typedef struct node { char e[100]; int top; }linkstack; typedef struct Node { float c[100]; int top; }link; char w[128]; int i; char prec[8][8]={">><<<>>",">><<<>>",">>>><>>", ">>>><>>","<<<<<=@",">>>>@>>", "<<<<<@=",">>>>>>>"}; char sign[]="+-*/()#"; char precede(char a,char b) { int i,j; i=j=0; while(sign[i]!=a) i++; while(sign[j]!=b) j++; return(prec[i][j]); } float numb() { int integer; float decimal=0; float sum=0; if(w[i]>='0'&&w[i]<='9') { integer=w[i]-'0'; i++; while(w[i]>='0'&&w[i]<='9') { integer=integer*10+w[i]-'0'; i++; } if(w[i]=='.') { float t=1.0; i++; while(w[i]>='0'&&w[i]<='9') { t=t/10; decimal=decimal+(w[i]-'0')*t; i++; } } sum=integer+decimal; return (sum); } else return(0); } void push1(linkstack *p,char c) { p->e[p->top++]=c; } void push2(link *p,float num) { p->c[p->top++]=num; } char gettop1(linkstack *optr) { char c; c=optr->e[optr->top-1]; return(c); } float gettop2(link *opnd) { float num; num=opnd->c[opnd->top-1]; return(num); } char pop1(linkstack *optr) { char c; c=optr->e[--optr->top]; return(c); } float pop2(link *opnd) { float num; num=opnd->c[--opnd->top]; return(num); } float operate(float a, char theta,float b) { float num; switch (theta) { case '+': num=b+a; break; case '-': num=b-a; break; case '*': num=a*b; break; case '/': num=b/a; break; } return num; } float evaluateexpression(void) { float num; char theta; float a,b; linkstack s; link t; s.top=0; t.top=0; push1(&s,'#'); i=0; while(w[i]!='#'||gettop1(&s)!='#') { num=numb(); if(num) { push2(&t,num); } else switch(precede(gettop1(&s),w[i])) { case'<': push1(&s,w[i++]);break; case'=': pop1(&s);i++;break; case'>': { theta=pop1(&s); a=pop2(&t); b=pop2(&t); push2(&t,operate(a,theta,b)); break; } } } return(gettop2(&t)); } void main() { float x; system("cls"); printf("表达式的计算!\n"); printf("输入表达式!\n"); scanf("%s",w); x=evaluateexpression(); printf("=%f",x); }