Data Structure Stack: Infix to Postfix

http://geeksquiz.com/stack-set-2-infix-to-postfix/

 1 #include <iostream>

 2 #include <vector>

 3 #include <algorithm>

 4 #include <queue>

 5 #include <stack>

 6 #include <string>

 7 #include <fstream>

 8 #include <map>

 9 #include <set>

10 using namespace std;

11 

12 bool isoprand(char x) {

13     return x >= 'A' && x <= 'Z' || x >= 'a' && x <= 'z';

14 }

15 

16 int prec(char x) {

17     if (x == '+' || x == '-') return 1;

18     if (x == '*' || x == '/') return 2;

19     if (x == '^') return 3;

20     return -1;

21 }

22 

23 int infixtopostfix(string s) {

24     string ans;

25     stack<char> T;

26     for (int i = 0; i < s.size(); i++) {

27         if (isoprand(s[i])) ans += s[i];

28         else if (s[i] == '(') T.push(s[i]);

29         else if (s[i] == ')') {

30             while (!T.empty() && T.top() != '(') {

31                 ans += T.top();

32                 T.pop();

33             }

34             if (!T.empty() && T.top() != '(') return -1;

35             T.pop();

36         }

37         else {

38             while (!T.empty() && prec(s[i]) <= prec(T.top())) {

39                 ans += T.top();

40                 T.pop();

41             }

42             T.push(s[i]);

43         }

44     }

45     while (!T.empty()) {

46         ans += T.top();

47         T.pop();

48     }

49     cout << ans << endl;

50 }

51 

52 int main() {

53     string s = "a+b*(c^d-e)^(f+g*h)-i";

54     infixtopostfix(s);

55     return 0;

56 }