C + + implements Infix expression pre-and suffix

#include <iostream> #include <string> #include <stack>using namespace std;bool isint (char ch) {if (ch    >= ' 0 ' &&ch<= ' 9 ') return true; return false;} BOOL Isoperator (char ch) {if (ch== ' + ' | | ch== '-' | | ch== ' * ' | |    ch== '/') return true; return false;}    int oplevel (char ch) {int level;        Switch (CH) {case ' + ': Case '-': level=1;    Break    Case ' * ': level=2;    Case '/': break;        default:level=0;    Break } return level; /* infix-to-prefix algorithm 1) to reverse the input string. 2) Check the next element of the input. 3) If it is an operand, add it to the output string. 4) If it is closed parenthesis, press it on the stack.    5) If the operator, then I) if the stack is empty, this operator into the stack.    II) If the top of the stack is a closing parenthesis, this operator is in the stack.    III) if its precedence is greater than or equal to the top of the stack operator, this operator is placed on the stack. IV) Otherwise, the stack top operator is out of the stack and added to the output string, repeating step 5. 6) In the case of open brackets, the operators in the stack stack and output until the closing brackets are encountered. Close the parentheses out of the stack and discard. 7) If the input is not complete, skip to step 2. 8) If the input is complete, all remaining operators in the stack are stacked and added to the output string. 9) The reverse of the output string.    */string Priorder (String mystr) {stack<char> opstack;    string result;        for (int i=mystr.length ()-1; i>=0; i--) {char ch=mystr[i]; if (Isint (ch)) {ResulT.push_back (CH);        } else if (') ' ==ch) {opstack.push (CH); } else if (Isoperator (CH))//operator {while (true) {if (Opstack.empty () | | | Opstack.top () = = ') ' | |                (Oplevel (CH) >=oplevel (Opstack.top ())))                    {Opstack.push (CH);                Break                    } else {Result.push_back (opstack.top ());                Opstack.pop ();                }}} and else if (' (' ==ch) {while (Opstack.top ()! = ') ') {                Result.push_back (Opstack.top ());            Opstack.pop ();        } opstack.pop ();        }} while (!opstack.empty ()) {Result.push_back (Opstack.top ());    Opstack.pop (); } return result;    /* infix-to-suffix algorithm */string postorder (String mystr) {string result;    Stack<char> Opstack; for (int i=0; i<mystr.length (); I+ +) {char ch=mystr[i];        if (Isint (ch)) {result.push_back (CH);        } else if (' (' ==ch) {opstack.push (CH); } else if (Isoperator (CH)) {while (true) {if (Opstack.empty () | | | Opstack.top () = = ' (' | |                    Oplevel (CH) >=oplevel (Opstack.top ())) {Opstack.push (CH);                Break                    } else {Result.push_back (opstack.top ());                Opstack.pop ();                }}}} else if (') ' ==ch) {while (Opstack.top ()! = ' (') {                Result.push_back (Opstack.top ());            Opstack.pop ();        } opstack.pop ();        }} while (!opstack.empty ()) {Result.push_back (Opstack.top ());    Opstack.pop (); } return result;    int main () {string mystr;    cin>>mystr; string RESult;    Result=priorder (MYSTR);    for (int i=result.length ()-1; i>=0; i--) {cout<<result[i];    } cout<<endl;    Result=postorder (MYSTR);    for (int i=0; i<=result.length (); i++) {cout<<result[i]; } return 0;}

　　

C + + implements Infix expression pre-and suffix