The application of infix expression and computing stack

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#include <iostream>#include<cstdio>#include<queue>#include<stack>using namespacestd;structPostfixexpre {stringinfix; Postfixexpre (string_infix) {infix=_infix; }    intGetpri (Charc) {Switch(c) { Case '(':                return 1;  Case '+': Case '-':                return 2;  Case '*': Case '/':                return 3;  Case ')':                return 4; default://Number returned 0                return 0; }    }    stringGetpostfix () {BOOLFrist =true; Stack<Char>s; stringPost; intn =infix.size ();  for(intI=0; i<N;) {            intPRI =Getpri (Infix[i]); Switch(PRI) { Case 0://if it is a number, add consecutive digits to the suffix                if(!frist)//used to go out the first spacePost + =" "; ElseFrist=false;  while(I<n &&!)Getpri (Infix[i])) Post+ = infix[i++];  Break;  Case 1://if yes (directly into the stackS.push (infix[i++]);  Break;  Case 2://if it is +-need to popup operator precedence in the stack than Infix[i], and add the prefix, and then infix[i] into the stack                 while(!s.empty () && Getpri (S.top ()) >=2) {Post+=" "; Post+=S.top ();                S.pop (); } s.push (Infix[i++]);  Break;  Case 3://if it is an operator with a higher or equal operator precedence than infix[i] in the */pop-up stack, and adds a prefix, then infix[i] into the stack                 while(!s.empty () && Getpri (S.top ()) >=3) {Post+=" "; Post+=S.top ();                S.pop (); } s.push (Infix[i++]);  Break;  Case 4://if yes) POPs all in the nearest (previous operator, and joins the suffix                 while(S.top ()! ='(') {Post+=" "; Post+=S.top ();                S.pop (); } s.pop (); //Eject (i++; }        }         while(!S.empty ()) {Post+=" "; Post+= +S.top ();        S.pop (); }        returnPost; }    voidPrintstack (stack<int>s) { while(!S.empty ()) {cout<<s.top () <<" ";        S.pop (); } cout<<Endl; }    BOOLIssinnum (intch) {        returnCH >=0&& CH <=9; }    //calculation of result by suffix expression requires a space between the suffix expression format number and the symbol, symbol, and symbol    intGetValue (stringPost) {Stack<int>s; intn =post.size ();  for(intI=0; i<N;) {            intres =0; Charc =Post[i]; if(c>='0'&& c<='9'){//if it is a number, extract all consecutive digits and put that number into the stack                 while(I<n && C! =' ') {res= res*Ten+c-'0'; C= post[++i]; } s.push (res);//Printstack (s);}Else{//is the symbol that pops up the stack in front of the two numbers and calculates and then results into the stack                intb =s.top (); S.pop (); intA =s.top (); S.pop (); Switch(c) { Case '+': res = a+b; Break;  Case '-': res = a-B; Break;  Case '*': res = a*b; Break;  Case '/': res = A/b; Break; } s.push (res);//Printstack (s);i++; } I++;//Skip Spaces        }        returnS.top (); }};intMain () {Postfixexpre P ("121+10* (53-49+20)/((35-25) *2+10) +11"); cout<<p.getpostfix () <<Endl; cout<<p.getvalue ("121 49-20 + * 25-2 * +/+ +");// $GetChar (); return 0;}

The application of infix expression and computing stack