Second largest array element in C

Finding the second largest value in an array is a classic C array program. This program gives you an insight of iteration, array and conditional operators. We iteratively check each element to determine the largest and second largest element.

Algorithm

Let's first see what should be the step-by-step procedure of this program −

START
   Step 1 → Take an array A and define its values
   Step 2 → Declare largest and second as integer
   Step 3 → Assign first two values of array A to largest and second
   Step 4 → Assign the large value to largest and second largest to second
   Step 5 → Iterate for Array A
   Step 6 → If A[n] > largest, Assign largest.value to second and Assign A[n] to largest
   Step 7 → Else If A[n] > second, Assign A[n] to second
   Step 8 → Loop Terminates
   Step 9 → Display largest and second
STOP

Pseudocode

Let's now see the pseudocode of this algorithm −

procedure largest_array(A)

   Declare largest and second as integer

   IF A[0] is greater than A[1] THEN 
      largest ← A[0]
      second ← A[1]
   ELSE
      largest ← A[1]
      second ← A[0]
   ENDIF

   FOR EACH value in A DO
      IF A[n] is greater than largest THEN
         second ← largest
         largest ← A[n]
      ELSE IF second is less than A[n] THEN
         second ← A[n]
      END IF

   END FOR
   Display largest and second

end procedure

Implementation

This pseudocode can now be implemented in the C program as follows −

#include <stdio.h>

int main() {
   int array[10] = {101, 11, 3, 4, 50, 69, 7, 8, 9, 0};
   int loop, largest, second;

   if(array[0] > array[1]) {
      largest = array[0];
      second  = array[1];
   } else {
      largest = array[1];
      second  = array[0];
   }

   for(loop = 2; loop < 10; loop++) {
      if( largest < array[loop] ) {
         second = largest;
         largest = array[loop];
      } else if( second < array[loop] ) {
         second =  array[loop];
      }
   }

   printf("Largest - %d \nSecond - %d \n", largest, second);   

   return 0;
}

The output should look like this −

Largest - 101
Second - 69