Question

in C programming

Assume that we have a series that is find as follows:

K1=1

K2=2

K3=3

K4=K1+K2+K3   

...

K(n) = K (n-1) + K(n-2) + K(n-3)

Here is the sequence:

1, 2, 3, 6, 11, 20, 37, ...

Write a code to print the Kth number in this sequence (not greater than 50) that is collected from the input (user will input a number smaller or equal to 50 and the program produce the entry in the series for that number).

Ex:

Inter an integer less than 50: 6

Output: 20

Answer 1

Please look at my code and in case of indentation issues check the screenshots.

------------main.c----------------

#include <stdio.h>

int main()
{
   int k;
   long int k1 = 1, k2 = 2, k3 = 3;   //initialize first 3 numbers of the series

   printf("Enter an integer less than 50: ");
   scanf("%d", &k);                   //read the value of k

   long int kthNumber;                   //we have to find kth number
   if(k == 1)                           //if k == 1, kth number is k1
       kthNumber = k1;
   else if(k == 2)                       //if k == 2, kth number is k2
       kthNumber = k2;
   else if(k == 3)                       //if k == 3, kth number is k3
       kthNumber = k3;  
   else if (k > 3){                  
       long int temp;
       for(int i = 4; i <= k; i++){   //loop from i = 4 to k
           temp = k1 + k2 + k3;       //keep adding previous three numbers
           k1 = k2;                   // (k1, k2, k3) ---> (k2, k3, k1+k2+k3)
           k2 = k3;
           k3 = temp;
       }
       kthNumber = k3;                   //kth number will be in k3
   }
   printf("Output: %ld\n", kthNumber);   //print output
   return 0;
}

--------------Screenshots-------------------

----------------------Output------------------------------------

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Note: We have used long int to store kth number, because for kthNumber is very large for k > 35, and int cannot hold all the digits. We need long int data type which can hold larger integers.

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