The **count-and-say sequence**, also known as the **look-and-say sequence**, is the following sequence of numbers:

$1, 11, 21, 1211, 111221, 312211, ...$

Starting from $1$, the best way to generate the next number in the sequence is to read the digits of the previous number, and then count​ the number of digits in groups of the same digit. For example:

# Implementation

- The `countAndSay` function takes a member of the count-and-say sequence as an argument and returns the ***next*** member in the sequence.
- The outer loop iterates over the argument string, `curr`. The inner loop counts the number of times the current digit is repeated; this is stored in the variable `count`. 
- Once a different digit is encountered, the count and the current digit itself are appended to `result`. For example, if $3$ **one's** were counted before the function came across a $2$, then "$31$" will be attached to `result`.

# Given a value 'curr', this function returns the value
# that comes after 'curr' in the look-and-say seq.
def countAndSay(curr):
    result = "" # to store the term after 'curr'
    i = 0 # to iterate over 'curr'
    # Need to iterate over 'curr', and also count the 
    # number of digits that occur in the same group 
    while i < len(curr):
        count = 1 # To store how many times a digit occured
        # Inner while loop compares current digit and the next digit
        while i + 1 < len(curr) and curr[i] == curr[i+1]:
            i += 1
            count += 1
        result += (str(count) + curr[i])
        i += 1
    return result

# Driver code
number = "1" # First member is always 1.
n = 6 # Number of members in the sequence
for i in range(n):
    print(number)
    number = countAndSay(number)

Python3

#include <iostream>
#include <sstream> // for int to string conversion

using namespace std;

// Utility function for integer to string conversion
string IntToString(int num)
{
    stringstream temp;
    temp << num;
    return temp.str();
}

// Given a value 'curr', this function returns the value
// that comes after 'curr' in the look-and-say seq.

string countAndSay(string curr)
{
  string result = ""; // To store the term after 'curr'
  int i = 0; // to iterate over 'curr'
  // Need to iterate over 'curr', and also count the 
  // number of digits that occur in the same group 
  
  while (i < curr.length())
  {
    int count = 1; // To store how many times a digit occured

    // inner while loop compares current digit and the next digit
    while ((i + 1 < curr.length()) && curr[i] == curr[i+1])
    {
      i++;
      count++;
    }
    // to append count to result, convert count to a string.
    string stringCount = IntToString(count);
    result += (stringCount + curr[i]);
    i++;
  }
  return result;

}

// driver code
int main()
{
  string number = "1"; // first member is always 1
  int n = 6; // number of members to print in the sequence
  for (int i = 0; i < n; i++)
  {
    cout << number << endl;
    number = countAndSay(number);
  }  
  return 0;
}

using System;

class CountAndSay
{
    static string CountNSay(string curr)
    {
      string result = "";
      int i = 0;
      while (i < curr.Length)
      {
        int count = 1;
        while ((i + 1 < curr.Length) && (curr[i] == curr[i+1]))
        {
          i += 1;
          count += 1;
        }
        result += (count.ToString() + curr[i]);
        i += 1;
      }
      return result;
    }
    public static void Main()
    {
        string number = "1"; // The first member is always 1
        int n = 6; // Number of members to print in the sequence
        for (int i = 0; i < n; i++)
        {
          Console.WriteLine(number);
          number = CountNSay(number);
        }  
    }
}

What is the count-and-say sequence algorithm?

The count-and-say sequence generates the next number by counting consecutive digits in the previous number.