Question

(a) Write a recursive function

int find(const int A[], int n, int x);

which returns the first index i = 0, . . . , n − 1 such that A[i] == x, or n if it is not found.

(b) Write a recursive function

int rfind(const int A[], int n, int x);

which returns the last index i = 0, . . . , n − 1 such that A[i] == x, or n if it is not found.

(c) Write a program search.cc which asks the user to enter the size of an array, the elements of an array, and an element to search for. For each set of input, the program should print the results of find and rfind. You should allocate the array dynamically. The program should be terminated when 0 is entered for the size of the array.

Answer 1

Solution:

#include <stdio.h>
#include <stdlib.h>
int currIndex = 0;
int find(const int A[], int n, int x){
   if(n==currIndex){
return n;
}

if(A[currIndex] == x){
return currIndex;
}
   currIndex++;
return find(A,n,x);
}

int rfind(const int A[], int n, int x){
  
   if(-1==currIndex){
return n;
}

if(A[currIndex] == x){
return currIndex;
}
   currIndex--;
return find(A,n,x);
}

int main(){
  
int x,n,i,*ptr;
printf("Enter the size of an array : ");
scanf("%d",&n);
  
if(n<=0){
   printf("Size can't be negative or zero");
   exit(0);
}

ptr = (int*) malloc(n*sizeof(int));
if(ptr == NULL)   
{
printf("Error! memory not allocated.");
exit(0);
}
  
printf("Enter all %d elements :\n",n);
for(i=0; i<n; i++){
   printf("Enter %d element :",i+1);
   scanf("%d",ptr +i);
}
printf("Enter an element to search : ");
scanf("%d",&x);
  
printf("\nfind() return value = %d \n",find(ptr,n,x));
currIndex = n-1;
printf("rfind() return value = %d \n ",rfind(ptr,n,x));
currIndex = 0;
free(ptr);

}

Output: