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C program to find two largest elements in a one dimensional array

Here, we are implementing a C program that finds the two largest numbers from a one dimensional array.
Submitted by Radib Kar, on December 05, 2018

Problem statement

Write a C program to find two largest elements in a one dimensional array.

Examples

Example: Type1: (all the elements are not same & no of element is more than two)

Input:
Array size: 4
Elements: 32 54 -6 43
    
Output: 
54 43

Example: Type2: (second maximum doesn’t exist as size of array < 2)

Input:
Array size : 1
Elements: 4

Output: 
4

Example: Type3: (all elements are same, thus only one largest element)

Input:
Array size : 4
Elements: 12 12 12 12
    
Output: 
12

Steps to find two largest elements in a an array

1. Define two variable max & sec_max
2. Initialize max to array[0] & sec_max to INT_MIN
3. Scan the entire array

a. For(int i=0;i<n;i++)
    if array[i]>max
    then update max to array[i]&sec_max to previous max value
    else if array[i] is greater than sec_max but less than max
        then update sec_max to array value
        do nothing to max
End for loop

4. If still sec_max has the value INT_MIN
   Only one largest value exists, print it
   Else
   Print max & sec_max

C program to find two largest elements in a one dimensional array

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

void findTwoMax(int* a, int n) {
  // initialize max to first array element
  int max = a[0];
  // initialize max to first array element
  int sec_max = INT_MIN, temp = 0;

  for (int i = 0; i < n; i++) {  // scan the entire array
    // if a[i]> max then update max to array value &
    // second max to previous max value
    if (a[i] > max) {
      sec_max = max;
      max = a[i];
    }
    // else if a[i] is greater than second max but less
    // than max then update second max to array value
    else if (a[i] > sec_max && a[i] < max)
      sec_max = a[i];
    // do nothing to max
  }
  // if second max is still at its initialized value
  // then no second maximum exists at all
  if (sec_max == INT_MIN)
    printf("only one large element: %d ", max);
  else
    printf("First largest element: %d  & second largest element : %d", max,
           sec_max);
}

int main() {
  int n;
  printf("enter no of elements\n");
  scanf("%d", &n);

  // dynamic array created
  int* a = (int*) malloc(sizeof(int) * n);

  printf("enter the elements........\n");
  // taking input
  for (int i = 0; i < n; i++) scanf("%d", &a[i]);

  // find two largest no
  findTwoMax(a, n);

  return 0;
}

Output

First run:
enter no of elements
4
enter the elements........
32 54 -6 43
First largest element: 54  & second largest element : 43

Second run:
enter no of elements
1
enter the elements........
4
only one large element: 4

Third run:
enter no of elements
4
enter the elements........
12 12 12 12
only one large element: 12

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