CODEWITHSUNDEEP
carrays
Bobby
Bobby

Reputation: 223

Index value won't change

I'm trying to implement a linear search function to search for a particular number in which the user "inputs" however, say for example the user wants to search for the number 3 in the given array. The function should return an index value of 2. But my code returns 6 no matter what input I enter. I suspect there is something wrong in my main function (maybe while I am using a for loop, the value of i gets fixed to 6?). Any ideas?

#include <stdio.h>
#include <stdlib.h>
#include <time.h>


#define numberOfElements 6
#define NOT_FOUND -1

int linearSearch (int *myArray, int key, int i);

int main (int argc, char *argv[]){

   int i, key, myArray[] = {1, 2, 3, 4, 5, 6};
   printf("Input: ");
   for (i = 0; i < numberOfElements; i++){
      printf("%d ", myArray[i]);
   }
   printf("\n");
   printf("Please enter a number you wish to search for: ");
   scanf("%d", &key);
   linearSearch (myArray, key, i);
   printf("The number %d is at index %d\n", key, i);

   return 0;
} 


int linearSearch (int *myArray, int key, int i) {

   for (i = 0; i < numberOfElements; i++){
      printf("Checking index %d\n", i);
      if (myArray[i] == key){
         printf("%d\n", i);
         return i;
         break;
      }
      printf("It's certainly not here!\n");
   }

   return NOT_FOUND;
}

Upvotes: 0

Views: 156

Answers (6)

isayme
isayme

Reputation: 319

After you first do the for loop to list your input array, the i value is 6.

Then you reuse the i as a parameter of linearSearch.

You should know that when you call linearSearch with parameter i, you just put the value of i to the stack, and in the dinner of the function, any change to i will not affect the value of outside i. So you always get a 6.

To correct this, you can change function call from
linearSearch (myArray, key, i);
to
i = linearSearch (myArray, key, i);

Then i will be changed to the return value.

Upvotes: 0

Dancrumb
Dancrumb

Reputation: 27549

You are not capturing the returned value of linearSearch.

You are passing it the value of i, but not a reference to i. Therefore, it doesn't matter what value you assign to it, it will not be available in linearSearch's calling context.

As a result, you are ignoring anything linearSearch does.

I'd suggest removing the third parameter from linearSearch and just capturing its return value in a new variable and printing that.

Make the i inside linearSearch a local variable instead of an input parameter.

int linearSearch (int *myArray, int key) {

   for (int i = 0; i < numberOfElements; i++){
      printf("Checking index %d\n", i);
      if (myArray[i] == key){
         printf("%d\n", i);
         return i;
         break;
      }
      printf("It's certainly not here!\n");
   }

   return NOT_FOUND;
}

/* ... */

int index = linearSearch (myArray, key);
printf("The number %d is at index %d\n", key, index);

Upvotes: 4

Attitude
Attitude

Reputation: 1

//It can work well if you correct it like this.

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define numberOfElements 6
#define NOT_FOUND -1

int linearSearch (int *myArray, int key, int& i); **//"int i" changed to "int& i"**

int main (int argc, char *argv[]){

   int i, key, myArray[] = {1, 2, 3, 4, 5, 6};
   printf("Input: ");
   for (i = 0; i < numberOfElements; i++){
      printf("%d ", myArray[i]);
   }
   printf("\n");
   printf("Please enter a number you wish to search for: ");
   scanf("%d", &key);
   linearSearch (myArray, key, i);
   if(i != numberOfElements)
   printf("The number %d is at index %d\n", key, i);

   return 0;
}


int linearSearch (int *myArray, int key, int& i) { //**"int i" changed to "int& i"**

   for (i = 0; i < numberOfElements; i++){
      printf("Checking index %d\n", i);
      if (myArray[i] == key){
         printf("%d\n", i);
         //return i; **//delete this statement**
         break;
      }
      printf("It's certainly not here!\n");
   }

   return NOT_FOUND;
}

Upvotes: -1

Amit009
Amit009

Reputation: 51

You need to take care of the following things.

  1. There is no use of passing the parameter i in function linearSearch. As you are not using the value passed.

  2. linearSearch function returns the value i.

    k= linearSearch (myArray, key);

then u can print the value like this.

 printf("The number %d is at index %d\n", key, k);

Upvotes: 0

monty_oso
monty_oso

Reputation: 29

Make this changes to your code:

    int linearSearch (int *myArray, int key);

    i = linearSearch (myArray, key);

    int linearSearch (int *myArray, int key, int i) {
      int i;

Upvotes: 0

William Morris
William Morris

Reputation: 3684

You ignore the return value from the linearSearch function. Hence you don't print the answer.

Note that you should not pass i into the function but instead declare it within the loop:

for (int i=0; i<... etc

Upvotes: 5

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