表达式求值（采用栈实现）

#include"Sqstack.h" #include"other.h" double EvluateExpression(char str[],LinkStack &OPTR,LinkStack1 &OPND) { int i=0,t,j,falg=0; double a,b,sum,s; char theta,x; InitStack(OPND); InitStack(OPTR); Push(OPTR,'#'); if(str[0]=='-') { Push(OPND,0); } while(str[i] !='#' || GetTop(OPTR)!='#') { if(str[i]>='0' && str[i]<='9') { sum=0; while(str[i]>='0' && str[i]<='9') //将整数保存到sum中 { sum=sum*10+str[i++]-'0'; } if(str[i]=='.') //如果有小数点，将j移动下一个运算符之前的字符，从那个字符开始往后依次除10，直到小数点之后的那一位字符，与sum相加 { s=0; j=i+1; while(str[j]>='0' && str[j]<='9') { j++; } for(t=j-1;t>i;t--) { s=s/10+str[t]-'0'; } s=s/10; //printf("%lf\n",s); sum=sum+s; i=j; } Push(OPND,sum); } else { if(str[i]=='-' && str[i-1]=='(') { Push(OPND,0); } switch(Precede(GetTop(OPTR),str[i])) { case '<': Push(OPTR,str[i]); i++; break; case '>': Pop(OPTR,theta); Pop(OPND,b);Pop(OPND,a); Push(OPND,Operate(a,theta,b)); break; case '=': Pop(OPTR,x); i++; break; } } } return GetTop(OPND); } char Precede(char a, char b) { int i,j; char Ns[7]={'+','-','*','/','(',')','#'}; char str[7][7]={'>','>','<','<','<','>','>', '>','>','<','<','<','>','>', '>','>','>','>','<','>','>', '>','>','>','>','<','>','>', '<','<','<','<','<','=',' ', '>','>','>','>',' ','>','>', '<','<','<','<','<',' ',' '}; for(i=0;i<7;i++) { if(Ns[i]==a) break; } for(j=0;j<7;j++) { if(Ns[j]==b) break; } return str[i][j]; } double Operate(double a,char op,double b) { switch(op) { case '+':return a+b;break; case '-':return a-b;break; case '*':return a*b;break; case '/':return a/b;break; } }