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Replace all occurrences of pi with 3.14 in a given string
• Difficulty Level : Medium
• Last Updated : 11 Jun, 2021

Given a string, the task is to replace all occurrences of pi with 3.14 in the given string.
Examples

```Input : str = "2 * pi + 3 * pi = 5 * pi"
Output : 2 * 3.14 + 3 * 3.14 = 5 * 3.14

Input : str = "pippppiiiipi"
Output : 3.14ppp3.14iii3.14

Input : str = "xpix"
Output : x3.14x```

Approach 1:

1. Create an empty output string.
2. Traverse the string from the 0th index till second last index since length of pi is 2.
3. If the alphabets at the current and (current+1)th index form the word “pi”, append “3.14” to the output string.
4. Else append the alphabet at the current index.

Below is the implementation of the above approach:

## C++

 `// C++ program to replace all``// pi in a given string with 3.14` `#include ``using` `namespace` `std;` `// Function to replace all occurrences``// of pi in a given with 3.14``string replacePi(string input)``{``    ``string output;` `    ``int` `size = input.length();` `    ``// Iterate through second last``    ``// element of the string``    ``for` `(``int` `i = 0; i < size; ++i) {` `        ``// If current and current +1 alphabets``        ``// form the word 'pi'``        ``// append 3.14 to output``        ``if` `(i + 1 < size and input[i] == ``'p'` `and input[i + 1] == ``'i'``) {``            ``output += ``"3.14"``;``            ``i++;``        ``}` `        ``// Append the current letter``        ``else` `{``            ``output += input[i];``        ``}``    ``}` `    ``// Return the output string``    ``return` `output;``}` `// Driver Code``int` `main()``{``    ``string input = ``"2 * pi + 3 * pi = 5 * pi"``;``    ``cout << replacePi(input);``    ``return` `0;``}`

## Java

 `// Java program to replace all``// pi in a given String with 3.14` `class` `GFG {` `    ``// Function to replace all occurrences``    ``// of pi in a given with 3.14``    ``public` `String replacePi(String input)``    ``{``        ``String output = ``""``;` `        ``int` `size = input.length();` `        ``// Iterate through second last``        ``// element of the String``        ``for` `(``int` `i = ``0``; i < size; ++i) {``            ``// If current and current +1 alphabets``            ``// form the word 'pi'``            ``// append 3.14 to output``            ``if` `(i + ``1` `< size && input.charAt(i) == ``'p'` `&& input.charAt(i + ``1``) == ``'i'``) {``                ``output += ``"3.14"``;``                ``i++;``            ``}` `            ``// Append the current letter``            ``else` `{``                ``output += input.charAt(i);``            ``}``        ``}` `        ``// Return the output String``        ``return` `output;``    ``}` `    ``// Driver Code``    ``public` `static` `void` `main(String args[])``    ``{``        ``GFG g = ``new` `GFG();``        ``String input = ``"2 * pi + 3 * pi = 5 * pi"``;``        ``System.out.println(g.replacePi(input));``    ``}``}` `// This code has been contributed by 29AjayKumar`

## Python3

 `# Python program to replace all``# pi in a given string with 3.14` `# Function to replace all occurrences``# of pi in a given with 3.14``def` `replacePi(``input``):``    ``output ``=``"";` `    ``size ``=` `len``(``input``);` `    ``# Iterate through second last``    ``# element of the string``    ``for` `i ``in` `range``(size):` `        ``# If current and current + 1 alphabets``        ``# form the word 'pi'``        ``# append 3.14 to output``        ``if` `(i ``+` `1` `< size ``and` `input``[i] ``=``=` `'p'` `and``                            ``input``[i ``+` `1``] ``=``=` `'i'``):``            ``output ``+``=` `"3.14"``;``            ``i``+``=` `1``;` `        ``# Append the current letter``        ``else``:``            ``output ``+``=` `input``[i];``    ``# Return the output string``    ``return` `output;` `# Driver Code``input` `=` `"2 * pi + 3 * pi = 5 * pi"``;``print``(replacePi(``input``));` `# This code contributed by PrinciRaj1992`

## C#

 `// C# program to replace all``// pi in a given string with 3.14` `using` `System;``// Function to replace all occurrences``// of pi in a given with 3.14``class` `gfg {``    ``public` `string` `replacePi(``string` `input)``    ``{``        ``string` `output = ``""``;` `        ``int` `size = input.Length;` `        ``// Iterate through second last``        ``// element of the string``        ``for` `(``int` `i = 0; i < size; ++i) {``            ``// If current and current +1 alphabets``            ``// form the word 'pi'``            ``// append 3.14 to output``            ``if` `(i + 1 < size && input[i] == ``'p'` `&& input[i + 1] == ``'i'``) {``                ``output += ``"3.14"``;``                ``i++;``            ``}` `            ``// Append the current letter``            ``else` `{``                ``output += input[i];``            ``}``        ``}` `        ``// Return the output string``        ``return` `output;``    ``}``}` `// Driver Code``class` `geek {``    ``public` `static` `int` `Main()``    ``{``        ``gfg g = ``new` `gfg();``        ``string` `input = ``"2 * pi + 3 * pi = 5 * pi"``;``        ``Console.WriteLine(g.replacePi(input));``        ``return` `0;``    ``}``}``// This code is contributed by Soumik`

## Javascript

 ``
Output:

`2 * 3.14 + 3 * 3.14 = 5 * 3.14`

Time Complexity: O(N), where N is the length of the given string.
Approach 2: (In Java)
To replace all the PI occurrences to 3.14, use replaceAll() method of Java String Class.

## Java

 `public` `class` `ReplacePI {``    ``public` `static` `void` `main(String[] args)``    ``{``        ``// Declare a String``        ``String expression = ``"2 * pi + 3 * pi = 5 * pi"``;` `        ``// Call replaceAll() method to replace PI to 3.14``        ``expression = expression.replaceAll(``"pi"``, ``"3.14"``);` `        ``// Print the result``        ``System.out.println(expression);``    ``}``}`
Output:
`2 * 3.14 + 3 * 3.14 = 5 * 3.14`

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