c++表达式求值实现.doc

1：工程结构 2：源代码 cpp: #includeiostream #includestdlib.h #includectype.h #includecmath using namespace std; typedef float type1; typedef char type2; struct zhan1 { type1 opnd[50]; int basic; int top; }; struct zhan2 { type2 optr[52]; int basic; int top; }; char yunsuan[8]={+,-,*,/,(,),#}; int priority[7][7]={ {3,3,1,1,1,3,3},{3,3,1,1,1,3,3},{3,3,3,3,1,1,3},{3,3,3,3,1,3,3},{1,1,1,1,1,2,0},{3,3,3,3,0,3,3},{1,1,1,1,1,0,2} }; int yunsuanfu(char c) { for(int i=0;i7;i++) { if(c==yunsuan[i]) { return 1; } } return 0; } int youxianji(char a,char b) { int ia=0; int ib=0; for(int i=0;i7;i++) { if(a==yunsuan[i]) { ia=i; break; } } for(i=0;i7;i++) { if(b==yunsuan[i]) { ib=i; break; } } return priority[ia][ib]; } int operate(int a,char the,int b) { char s[5]={+,-,*,/}; if(the==s[0]) return a+b; if(the==s[1]) return a-b; if(the==s[2]) return a*b; if(the==s[3]) return a/b; } void main() { zhan1 s1; zhan2 s2; s1.top=0;s1.basic=0; s2.top=0;s2.basic=0; s1.opnd[s1.top]=0; char c; s2.optr[s2.top]=#; c=getchar(); while(c!=#||s2.optr[s2.top]!=#) { if(yunsuanfu(c)) { switch(youxianji(s2.optr[s2.top],c)) { case 0:cout输入操作符错误，重新输入：endl;c=getchar();break; case 1:s2.top++;s2.optr[s2.top]=c;c=getchar();break; case 2:s2.top--;c=getchar();break; case 3:char theta=s2.optr[s2.top];s2.top--;float b=s1.opnd[s1.top-1];s1.top--;float a=s1.opnd[s1.top-1];s1.top--;float answer=operate(a,theta,b);s1.opnd[s1.top]=answer;s1.top++;break; } } else { if(isdigit(c)) { float shuzi[12]; int i=0; double s=0.0; float zhi=0; shuzi[i]=(float)c-48.0; i++; c=getchar(); while(isdigit(c)i=11) { shuzi[i]=(float)c-48.0; i++; c=getchar(); } s=i; for(int j=0;ji;j++) { float m=pow(10.0,s-1.0); zhi=zhi+m*shuzi[j]; s--; } s1.opnd[s1.top]=zhi; s1.top++;