Question

Use C++ Language to program evaluation using Prefix and Postfix and use stacks and queues Math expression and converts the same to its forms.

Infix: 3 + 2 - 5 * 8 + 3

Prefix: - + 3 2 + * 5 8 3

Postfix: 3 2 + 5 8 * - 3 +

Answer 1

CODE:

// using ,stack infix to postfix ......
#include <bits/stdc++.h>
using namespace std;

bool isOperator(char c)
{
return (!isalpha(c) && !isdigit(c));
}

int getPriority(char C)
{
if (C == '-' || C == '+')
return 1;
else if (C == '*' || C == '/')
return 2;
else if (C == '^')
return 3;
return 0;
}

string infixToPostfix(string infix)
{
infix = '(' + infix + ')';
int l = infix.size();
stack<char> char_stack;
string output;

for (int i = 0; i < l; i++) {

// If the scanned character is an
// operand, add it to output.
if (isalpha(infix[i]) || isdigit(infix[i]))
output += infix[i];
   // If the scanned character is an
// ‘(‘, push it to the stack.
else if (infix[i] == '(')
char_stack.push('(');

// If the scanned character is an
// ‘)’, pop and output from the stack
// until an ‘(‘ is encountered.
else if (infix[i] == ')') {

while (char_stack.top() != '(') {
output += char_stack.top();
char_stack.pop();
}

// Remove '(' from the stack
char_stack.pop();
}

// Operator found
else {
  
if (isOperator(char_stack.top())) {
while (getPriority(infix[i])
<= getPriority(char_stack.top())) {
output += char_stack.top();
char_stack.pop();
}

// Push current Operator on stack
char_stack.push(infix[i]);
}
}
}
return output;
}

string infixToPrefix(string infix)
{
/* Reverse String
* Replace ( with ) and vice versa
* Get Postfix
* Reverse Postfix * */
int l = infix.size();

// Reverse infix
reverse(infix.begin(), infix.end());

// Replace ( with ) and vice versa
for (int i = 0; i < l; i++) {

if (infix[i] == '(') {
infix[i] = ')';
i++;
}
else if (infix[i] == ')') {
infix[i] = '(';
i++;
}
}

string prefix = infixToPostfix(infix);

// Reverse postfix
reverse(prefix.begin(), prefix.end());

return prefix;
}

// Driver code
int main()
{
string s = "3+2-5*8+3";
cout << infixToPrefix(s) << std::endl;
return 0;
}

Input Snapshots:

2 3 // using ,stack infix to postfix ...... #include <bits/stdc++.h> using namespace std; 5 bool isoperator (char c) 60 7 return (!isalpha (c) && !isdigit(c)); 8L) 10 11 B W int getPriority (char C) { if (c == '-' II C = "+") return 1; else if (C == '*' II C == '/') return 2; else if (c == "") return 3; return 0; loco Join 20 21 22 23 string infixTo Postfix (string infix) { infix = '( + infix + ''; int i = infix.size(); stack<char> char_stack; string output; 24 25 26 28 for (int i = 0; i < l; i++) { // If the scanned character is an // operand, add it to output. if (isalpha (infix[i]) 11 isdigit (infix[i]))

output += infix[i]; // If the scanned character is an // 'C', push it to the stack. else if (infix[i] == '(') char_stack.push(' '); // If the scanned character is an // ', pop and output from the stack // until an 'i' is encountered. else if (infix[i] == ')') { while (char_stack.top() != '(') { output += char_stack.top(); char_stack.pop(); POCO OWNPO ocoon WMO cani w // Remove 'l' from the stack char_stack.pop(); // Operator found else { if (isOperator (char_stack.top())) { while (getPriority (infix[i]) <= getPriority (char_stack.top())) { output += char_stack.top(); char_stack.pop();

// Push current Operator on stack char_stack.push(infix[i]); un o return output; 69 L) 71 72 73 string infixTo Prefix (string infix) { /* Reverse String * Replace (with) and vice versa * Get Postfix * Reverse Postfix * */ int i = infix.size(); // Reverse infix reverse (infix.begin(), infix.end()); // Replace ( with ) and vice versa for (int i = 0; i < 1; i++) { Nocojon WN O Cow 85 if (infix[i] == '() { infix[i] = '); i++; 0 else if (infix[i] == '') { infix[i] = ''; i++; 0

string prefix = infixto Postfix (infix); // Reverse postfix reverse (prefix.begin(), prefix.end()); 100 return prefix 101 L) 102 103 // Driver code 104 int main() 105 { string s = "3+2-5*8+3"; 107 cout << infixTo Prefix (s) << std::endl; 108 return 0; 109 L 106

Output Snapshots:

- O X C:\Program Files (x86)\Dev-Cpp\ConsolePauser.exe +3-2+*583 Process exited normally. Press any key to continue ...