# Prefix to Infix Conversion

Infix : An expression is called the Infix expression if the operator appears in between the operands in the expression. Simply of the form (operand1 operator operand2).
Example : (A+B) * (C-D)

Prefix : An expression is called the prefix expression if the operator appears in the expression before the operands. Simply of the form (operator operand1 operand2).
Example : *+AB-CD (Infix : (A+B) * (C-D) )

Given a Prefix expression, convert it into a Infix expression.
Computers usually does the computation in either prefix or postfix (usually postfix). But for humans, its easier to understand an Infix expression rather than a prefix. Hence conversion is need for human understanding.

Examples:

```Input :  Prefix :  *+AB-CD
Output : Infix : ((A+B)*(C-D))

Input :  Prefix :  *-A/BC-/AKL
Output : Infix : ((A-(B/C))*((A/K)-L))

```

Algorithm for Prefix to Infix

• Read the Prefix expression in reverse order (from right to left)
• If the symbol is an operand, then push it onto the Stack
• If the symbol is an operator, then pop two operands from the Stack
Create a string by concatenating the two operands and the operator between them.
string = (operand1 + operator + operand2)
And push the resultant string back to Stack
• Repeat the above steps until end of Prefix expression.

## C++

 `// C++ Program to convert prefix to Infix` `#include ` `#include ` `using` `namespace` `std;`   `// function to check if character is operator or not` `bool` `isOperator(``char` `x) {` `  ``switch` `(x) {` `  ``case` `'+'``:` `  ``case` `'-'``:` `  ``case` `'/'``:` `  ``case` `'*'``:` `    ``return` `true``;` `  ``}` `  ``return` `false``;` `}`   `// Convert prefix to Infix expression` `string preToInfix(string pre_exp) {` `  ``stack s;`   `  ``// length of expression` `  ``int` `length = pre_exp.size();`   `  ``// reading from right to left` `  ``for` `(``int` `i = length - 1; i >= 0; i--) {`   `    ``// check if symbol is operator` `    ``if` `(isOperator(pre_exp[i])) {`   `      ``// pop two operands from stack` `      ``string op1 = s.top();   s.pop();` `      ``string op2 = s.top();   s.pop();`   `      ``// concat the operands and operator` `      ``string temp = ``"("` `+ op1 + pre_exp[i] + op2 + ``")"``;`   `      ``// Push string temp back to stack` `      ``s.push(temp);` `    ``}`   `    ``// if symbol is an operand` `    ``else` `{`   `      ``// push the operand to the stack` `      ``s.push(string(1, pre_exp[i]));` `    ``}` `  ``}`   `  ``// Stack now contains the Infix expression` `  ``return` `s.top();` `}`   `// Driver Code` `int` `main() {` `  ``string pre_exp = ``"*-A/BC-/AKL"``;` `  ``cout << ``"Infix : "` `<< preToInfix(pre_exp);` `  ``return` `0;` `}`

## Java

 `// Java program to convert prefix to Infix ` `import` `java.util.Stack;`   `class` `GFG{`   `// Function to check if character` `// is operator or not     ` `static`    `boolean` `isOperator(``char` `x) ` `{` `    ``switch``(x)` `    ``{` `        ``case` `'+'``:` `        ``case` `'-'``:` `        ``case` `'*'``:` `        ``case` `'/'``:` `            ``return` `true``;` `    ``}` `    ``return` `false``;` `}`   `// Convert prefix to Infix expression ` `public` `static` `String convert(String str)` `{` `    ``Stack stack = ``new` `Stack<>();` `    `  `    ``// Length of expression ` `    ``int` `l = str.length();` `    `  `    ``// Reading from right to left ` `    ``for``(``int` `i = l - ``1``; i >= ``0``; i--)` `    ``{` `        ``char` `c = str.charAt(i);` `        ``if` `(isOperator(c))` `        ``{` `            ``String op1 = stack.pop();` `            ``String op2 = stack.pop();` `            `  `            ``// Concat the operands and operator ` `            ``String temp = ``"("` `+ op1 + c + op2 + ``")"``;` `            ``stack.push(temp);` `        ``} ` `        ``else` `        ``{` `            `  `            ``// To make character to string` `            ``stack.push(c + ``""``); ` `        ``}` `    ``}` `    ``return` `stack.pop();` `}`   `// Driver code` `public` `static` `void` `main(String[] args)` `{` `    ``String exp = ``"*-A/BC-/AKL"``;` `    ``System.out.println(``"Infix : "` `+ convert(exp));` `}` `}`   `// This code is contributed by abbeyme`

## C#

 `// C# program to convert prefix to Infix ` `using` `System;` `using` `System.Collections;`   `class` `GFG{` ` `  `// Function to check if character` `// is operator or not     ` `static` `bool` `isOperator(``char` `x) ` `{` `    ``switch``(x)` `    ``{` `        ``case` `'+'``:` `        ``case` `'-'``:` `        ``case` `'*'``:` `        ``case` `'/'``:` `            ``return` `true``;` `    ``}` `    ``return` `false``;` `}` ` `  `// Convert prefix to Infix expression ` `public` `static` `string` `convert(``string` `str)` `{` `    ``Stack stack = ``new` `Stack();` `     `  `    ``// Length of expression ` `    ``int` `l = str.Length;` `     `  `    ``// Reading from right to left ` `    ``for``(``int` `i = l - 1; i >= 0; i--)` `    ``{` `        ``char` `c = str[i];` `        `  `        ``if` `(isOperator(c))` `        ``{` `            ``string` `op1 = (``string``)stack.Pop();` `            ``string` `op2 = (``string``)stack.Pop();` `             `  `            ``// Concat the operands and operator ` `            ``string` `temp = ``"("` `+ op1 + c + op2 + ``")"``;` `            ``stack.Push(temp);` `        ``} ` `        ``else` `        ``{` `            `  `            ``// To make character to string` `            ``stack.Push(c + ``""``); ` `        ``}` `    ``}` `    ``return` `(``string``)stack.Pop();` `}` ` `  `// Driver code` `public` `static` `void` `Main(``string``[] args)` `{` `    ``string` `exp = ``"*-A/BC-/AKL"``;` `    `  `    ``Console.Write(``"Infix : "` `+ convert(exp));` `}` `}`   `// This code is contributed by rutvik_56`

Output:

```Infix : ((A-(B/C))*((A/K)-L))

```

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.

My Personal Notes arrow_drop_up Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.

Improved By : abhy1209120, rutvik_56