Program to find largest and second largest number in array

Question

I have searched many websites for this question  They are doing it by some different approach  This code is just not giving output if I input first element of array as largest i e  a 0   I think some minor change is required  can anyone please tell me    include  lt stdio h gt   int main         int a 10   n      int largest1  largest2  i       printf  enter number of elements you want in array        scanf   d    amp n       printf  enter elements        for  i   0  i  lt  n  i              scanf   d    amp a i              largest1   a 0       for  i   0  i  lt  n  i              if  a i   gt  largest1                largest1   a i                       largest2   a 0       for  i   1  i  lt  n  i              if  a i   gt  largest2  amp  amp  a i   lt  largest1              largest2   a i             printf  First and second largest number is  d and  d    largest1  largest2

User · Answer

The problem with your code is a logic problem (which is what most coding is about). If the largest number is first then it gets the second largest number wrong ... why?

Well, look at your logic for deciding on the second largest number. You first set it to be equal to the first element in the array and then you go through the array and change the index if the element is greater than the current second largest number (which will never be true because we already set it to be the largest number!).

To solve it you can special case this: check if the largest number was the first and if so then set it to the second element (and then special case the issue of someone asking to find the highest two elements in a one element array, without reading past the end of an array.)

I think the method given in chqrlie's answer to do this all in one pass is best. And logical too: write a program to find the largest number. Second largest number, well that's just the one which was previously the largest!

User · Answer

If you ever need to find the largest or smallest element in an array  try with bubble sort  Bubble Sort works on simple concept of shifting the biggest element at the end in every pass it does  in case of increasing order   Since you need the first and second largest element in an array  2 passes of bubble sort will do the trick  The last element will be the largest and the second last element will be second largest  I m providing you with the link that ll help you understand the bubble sort concept   http   www codeido com 2010 10 bubblesort-written-in-c-with-example-step-by-step   Hope it helps

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Here is an answer with a single for loop   int array       10  15  13  20  21  8  6  7  9  21  23    const int count   sizeof a    sizeof a 0    int lastMaxNumber   0  int maxNumber   0   for  int i   0  i  lt  count  i              Current number     int num   array i           Find the minimum and maximum from  num  max      int maxValue    num  gt  maxNumber    num   maxNumber      int minValue    num  lt  maxNumber    num   maxNumber          If minValue is greater than lastMaxNumber  update the lastMaxNumber     if minValue  gt  lastMaxNumber           lastMaxNumber   minValue                Updating maxNumber     maxNumber   maxValue     printf   d   lastMaxNumber

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There is no need to use the Third loop to check the second largest number in the array  You can only use two loops one for insertion and another is for checking   Refer this code    include  lt stdio h gt   int main      int a 10   n   int i   printf  enter number of elements you want in array     scanf   d    amp n    printf  enter elements     for  i   0  i  lt  n  i          scanf   d    amp a i       int largest1   a 0  largest2   a 0    for  i   0  i  lt  n  i           if  a i   gt  largest1                  largest2 largest1           largest1   a i            printf  First and second largest number is  d and  d    largest1  largest2       Hope this code will work for you   Enjoy Coding

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Try Out with this       firstMax   arr 0        for  int i   0  i lt n  i               if  firstMax  lt  arr i                   secondMax   firstMax              firstMax   arr i

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The question is ambiguous  if the array may contain duplicate values  are you supposed to find the 2 largest distinct values or the two largest possibly identical values   Your code seems to indicate you want the first approach  but you have a problem if the largest value is a 0    You should use an extra boolean to keep track of whether you have found a different value yet   You should also test the return value of the different scanf   calls and return 0 from main     Here is a modified version    include  lt stdio h gt   int main void        int a 10   n  i      int largest1  largest2  has largest2       printf  enter number of elements you want in array          if  scanf   d    amp n     1          return 1      if  n  lt  2            printf  need at least 2 elements n            return 1            printf  enter elements          for  i   0  i  lt  n  i              if  scanf   d    amp a i      1                printf  input error n                return 1                      largest1   a 0       for  i   1  i  lt  n  i              if  a i   gt  largest1                largest1   a i                       has largest2   largest2   0      for  i   0  i  lt  n  i              if  a i   lt  largest1                if   has largest2                    has largest2   1                  largest2   a i                 else             if  a i   gt  largest2                    largest2   a i                                     if  has largest2            printf  First and second largest number is  d and  d n                  largest1  largest2         else           printf  All values are identical to  d n   largest1             return 0

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Try this   public static void main String   args  throws IndexOutOfBoundsException        int   a     12  19  10  3  9  8        int n   a length      int larg   a 0       int larg2   a 0        for  int i   0  i  lt  n  i              if  larg  lt  a i                 larg   a i                      if  a i   gt  larg2  amp  amp  larg  lt  a i                 larg2   a i                         System out println  largest     larg       System out println  largest2     larg2

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Getting the second largest number from an array is pretty easy in python  I have done with simple steps and put various ways of test cases and it gave the right answer every time  PS  I know it s for c but I just gave a simple solution to the question if done in python  n   int input     taking number of elements in array arr   map int  input   split     taking differet elements l    s set   for i in arr   putting all the elemnents in set to remove any duplicate number     s add i  for j in s    putting all element from the set in the list to sort and get the second largest number     l append j  l sort   c len l  print l c-2    printing second largest number

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If you need to find the largest and second largest element in an existing array  see the answers above  Schwern s answer contains the approach I would ve used    However  needing to find the largest and second largest element in an existing array typically indicates a design flaw  Entire arrays don t magically appear - they come from somewhere  which means that the most efficient approach is to keep track of  current largest and current second largest  while the array is being created   For example  for your original code the data is coming from the user  and by keeping track of  largest and second largest value that the user entered  inside of the loop that gets values from the user the overhead of tracking the information will be hidden by the time spent waiting for the user to press key s  you no longer need to do a search afterwards while the user is waiting for results  and you no longer need an array at all   It d be like this   int main         int largest1   0  largest2   0  i  temp       printf  enter number of elements you want in array        scanf   d    amp n       printf  enter elements        for  i   0  i  lt  n  i              scanf   d    amp temp           if temp  gt   largest1                largest2   largest1              largest1   temp            else if temp  gt  largest2                largest2   temp                      printf  First and second largest number is  d and  d    largest1  largest2

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Find your second largest number without using any String function   int array     Input array int firstLargest  secondLargest  int minNumber   -1   whatever smallest you want to add here   There should be more than two elements   if  array size  lt  2        printf  Array is too small        return     firstLargest   secondLargest   minNumber  for  index   0  index  lt  array size     index          Largest number check     if  array index   gt  first                secondLargest   firstLargest          firstLargest   array index                It may not larger than first but can be larger than second number     else if  array index   gt  secondLargest  amp  amp  array index     firstLargest            secondLargest   array index        Finally you got your answer if  secondLargest    minNumber        printf  No Second largest number      else       printf  Second Largest Number is  d   secondLargest

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You need to preserve the index of array members better as they are unique Here is a working code with few changes    include lt stdio h gt  int main         int a 10  n      int largest1 largest2 i       printf  enter number of elements you want in array        scanf   d   amp n       printf  enter elements        for i 0 i lt n i                  scanf   d   amp a i              largest1 0      for i 0 i lt n i                  if a i  gt a largest1                         largest1 i                      if largest1  0     this condition to select another index than the largest         largest2 0      else         largest2 n-1      for i 0 i lt n  amp  amp  i    largest1  i                  if a i  gt a largest2               largest2 i            printf  First and second largest number is  d and  d   a largest1  a largest2        Note that when the array is of size 1 values will be the same

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I m going to ignore handling input  its just a distraction    The easy way is to sort it    include  lt stdlib h gt   include  lt stdio h gt   int cmp int  const void  a  const void  b         return   int  a -   int  b     int main         int a       1  5  3  2  0  5  7  6        const int n   sizeof a    sizeof a 0         qsort a  n  sizeof a 0    cmp int       printf   d  d n   a n-1   a n-2        But that isn t the most efficient because it s O n log n   meaning as the array gets bigger the number of comparisons gets bigger faster  Not too fast  slower than exponential  but we can do better   We can do it in O n  or  linear time  meaning as the array gets bigger the number of comparisons grows at the same rate   Loop through the array tracking the max  that s the usual way to find the max  When you find a new max  the old max becomes the 2nd highest number   Instead of having a second loop to find the 2nd highest number  throw in a special case for running into the 2nd highest number    include  lt stdio h gt   include  lt limits h gt   int main         int a       1  5  3  2  0  5  7  6           This trick to get the size of an array only works on stack allocated arrays      const int n   sizeof a    sizeof a 0            Initialize them to the smallest possible integer         This avoids having to special case the first elements      int max   INT MIN      int second max   INT MIN       for  int i   0  i  lt  n  i                  Is it the max          if  a i   gt  max                    Make the old max the new 2nd max              second max   max                 This is the new max              max   a i                        It s not the max  is it the 2nd max          else if  a i   gt  second max                 second max   a i                        printf  max   d  second max   d n   max  second max       There might be a more elegant way to do it  but that will do  at most  2n comparisons  At best it will do n   Note that there s an open question of what to do with   1  2  3  3    Should that return 3  3 or 2  3  I ll leave that to you to decide and adjust accordingly

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You can do it best in one pass   largest and largest2 are set to INT MIN on entry  Then step through the array  If largest is smaller than the number  largest2 becomes largest  then largest becomes the new number  or smaller than or equal if you want to allow duplicates   If largest is greater then the new number  test largest2   Note that this algorithm scales to finding the top three or four in an array  before it become too cumbersome and it s better to just sort

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Although it can be done in one scan but to correct your own code   you must declare largest2 as int Min as it prevents the largest2 holding the largest value intially

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include lt stdio h gt   int main         int a 10       int i b c       printf  Enter ten values    n        for i 0  i lt 10  i                  scanf   d   amp a i               b a 0        for i 0  i lt 10  i                  if a i  gt b                        b a i                      else                       b b                       if b  a 1                 c a 2             else                c a 1              for i 0  i lt 10  i                  if a i  gt c  amp  amp  a i   b                        c a i                      else if  b gt c                        c c                           printf  Largest number is  d nSecond largest number is  d  b c

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I think its simple like   include lt stdio h gt  int main      int a1 100  a2 100  i t l1 l2 n  printf  Enter the number of elements  n    scanf   d   amp n   printf  Enter the elements  n    for i 0 i lt n i          scanf   d   amp a1 i      l1 a1 0   for i 0 i lt n i          if a1 i  gt  l1                l1 a1 i           t i          for i 0 i lt  n-1  i          if i  t                continue            else               a2 i  a1 i           l2 a2 0   for i 1 i lt  n-1  i          if a2 i  gt  l2  amp  amp  a2 i  lt l1                l2 a2 i           printf  Second highest number is  d  l2   return 0

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package secondhighestno   import java util Scanner              author Laxman     public class SecondHighestno                    param args the command line arguments             public static void main String   args               TODO code application logic here         Scanner sc new Scanner System in           int n  sc nextInt            int a   new int n           for int i 0 i lt n i                 a i  sc nextInt                      int max1 a 0  max2 a 0           for int j 0 j lt n j                 if a j  gt max1                   max1 a j                                   for int k 0 k lt n k                 if a k  gt max2  amp  amp  max1 gt a k                    max2 a k                                   System out println max1     max2

[c] Program to find largest and second largest number in array

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