#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int arr[21];

int max(int n)
{
 	int max_value, max_index = 0, i;

  max_value = arr[max_index];
  for (i = 0; i <= n; i++)
    if (arr[i] > max_value) {
      max_value = arr[i];
      max_index = i;
    }
  return max_index;
}

void sort(int n)
{
  int largest, temp;

  if (n <= 1) return;
  largest = max(n - 1);
  temp = arr[largest];
  arr[largest] = arr[n - 1];
  arr[n - 1] = temp;
  sort(n - 1);
}

float powe(float x, int a, int n)
{
	if(a == 0)
		return 1;
	if(n == a)
		return x;
	else
		return x * powe(x,a,n+1);
}

int palin(char str[],int n)
{
	if(n<strlen(str)/2)
	{
		if(str[n] == str[strlen(str)-n-1])
			return palin(str,n+1);
		else
			return 0;
	}
	else
	{
		return 1;
	}
	
}

int fact(int x, int n)
{
	if(n == x)
		return x;
	else
		return n*fact(x,n+1);
}

int search(char arr[], char n, int i)
{
	if(i == strlen(arr))
		return 0;
	else
	{
		if(n == arr[i])
			return 1 + search(arr,n,i+1);
		else
			return 0 + search(arr,n,i+1);
	}
}



int bin(char chh,int first, int last)
{
	int mid;
	if(first <= last)
	{
		mid = (first + last) / 2;
		if(chh == arr[mid])
			return 1;
		else if(chh < arr[mid])
			return bin(chh,first,mid-1);
		else
			return bin(chh,mid+1,last);
	}
	else
		return -1;
}


int main()
{
	float x;
	int a,ch,i;
	char chh;
	while(1)
	{
		printf("Choose one of the following:\n1. Palindrome\n2. x^a\n3. x!\n4. Number of occurrences\n5. Binary Search\n6. Exit\nEnter your choice: ");
		scanf("%d",&ch);
		//fflush(NULL);
		getchar();
		if(ch == 1)
		{
			char tmp[256];
			printf("Enter a string (max 20 char): ");
			gets(tmp);
	
			if(palin(tmp,0))
				printf("This string is a palindrome\n");
			else
				printf("This string is not a palindrome\n");
		}
		else if(ch == 2)
		{
			printf("Enter value for x:");	
			scanf("%f",&x);
			printf("Enter value for a:");
			scanf("%d",&a);
			printf("x^a = %f\n",powe(x,a,1));
		}
		else if(ch == 3)
		{
			printf("Enter value for x:");
			scanf("%f",&x);
			printf("x! = %d\n",fact(x,1));
		}
		else if(ch == 4)
		{
			char temp[256];
			printf("Enter a string (max 20 char): ");
			gets(temp);
			printf("%c occurs %d times in '%s'\n",temp[0],search(temp,temp[0],0),temp);
		}
		else if(ch == 5)
		{
			int index = 0, temp;
		  printf("Enter integers, ending with -1.\n");
		  do 
			{
		    scanf("%d", &temp);
    		if (index >= 20) 
				{	
			  	printf("EXCEEDED ARRAY SIZE of 20\n");
	       break;
   		  } 
				else 
				{
       		arr[index] = temp;
		      index++;
    		 }
		  } while (temp != -1);

			printf("Enter the number to be searched: ");
			scanf("%d",&a);
			sort(index-1);
			a = bin(a,0,index-1);
			if(a==-1)
				printf("Number not found\n");
			else
				printf("Number found\n");
		}
		else if(ch == 6)
		{
			exit(0);
		}
		else
		{
			printf("Invalid choice, choose again\n");
		}
	}
}