Check if element found in array c

Question

How can I check if my array has an element I m looking for   In Java  I would do something like this   Foo someObject   new Foo someParameter   Foo foo    search through Foo   arr for int i   0  i  lt  arr length  i       if arr i  equals someObject      foo   arr i     if  foo    null    System out println  Not found     else   System out println  Found       But in C   I don t think I m allowed to search if an Object is null so what would be the C   solution

User · Answer

You would just do the same thing  looping through the array to search for the term you want  Of course if it s a sorted array this would be much faster  so something similar to prehaps   for int i   0  i  lt  arraySize  i          if array i     itemToFind            break

User · Answer

You can use old C-style programming to do the job  This will require little knowledge about C     Good for beginners   For modern C   language you usually accomplish this through lambda  function objects      or algorithm  find  find if  any of  for each  or the new for  auto amp  v   container      syntax   find class algorithm takes more lines of code  You may also write you own template find function for your particular need   Here is my sample code   include  lt iostream gt   include  lt functional gt   include  lt algorithm gt   include  lt vector gt   using namespace std          This is old C-like style   It is mostly gong from     modern C   programming   You can still use this    since you need to know very little about C        param storeSize you have to know the size of store       How many elements are in the array      return the index of the element in the array       if not found return -1     int in array const int store    const int storeSize  const int query       for  size t i 0  i lt storeSize    i          if  store i     query             return i                  return -1     void testfind        int iarr       3  6  8  33  77  63  7  11           for beginners  it is good to practice a looping method    int query   7     if  in array iarr  8  query     -1          cout  lt  lt  query  lt  lt    is in the array n               using vector or list      any container in C      vector lt int gt  vecint  3  6  8  33  77  63  7  11       auto it find vecint begin    vecint end    query      cout  lt  lt   using find   n      if  it    vecint end            cout  lt  lt   found    lt  lt  query  lt  lt    in the container n           else         cout  lt  lt   your query     lt  lt  query  lt  lt    is not inside the container n            using namespace std  placeholders        here the query variable is bound to the  equal to  function        object  defined in std     cout  lt  lt   using any of n      if  any of vecint begin    vecint end    bind equal to lt int gt      1  query            cout  lt  lt   found    lt  lt  query  lt  lt    in the container n           else         cout  lt  lt   your query     lt  lt  query  lt  lt    is not inside the container n               using lambda  here I am capturing the query variable       into the lambda function    cout  lt  lt   using any of with lambda  n      if  any of vecint begin    vecint end                 query  int val - gt bool  return val  query              cout  lt  lt   found    lt  lt  query  lt  lt    in the container n           else         cout  lt  lt   your query     lt  lt  query  lt  lt    is not inside the container n           int main int argc  char  argv         testfind        return 0      Say this file is named  testalgorithm cpp  you need to compile it with  g   -std c  11 -o testalgorithm testalgorithm cpp   Hope this will help  Please update or add if I have made any mistake

User · Answer

There are many ways   one is to use the std  find   algorithm  e g    include  lt algorithm gt   int myArray       3  2  1  0  1  2  3    size t myArraySize   sizeof myArray    sizeof int   int  end   myArray   myArraySize     find the value 0  int  result   std  find myArray  end  0   if  result    end         found value at  result  pointer location

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If you were originally looking for the answer to this question  int value in sorted  Ascending  int array   then you can use the following code that performs a binary search  fastest result    static inline bool exists int ints    int size  int k     array  array s size  searched value       if  size  lt   0          check that array size is not null or negative          return false         sort ints  ints   size      uncomment this line if array wasn t previously sorted     return  std  binary search ints  ints   size  k        edit  Also works for unsorted int array if uncommenting sort

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You can do it in a beginners style by using control statements and loops    include  lt iostream gt  using namespace std  int main        int arr      10 20 30 40 50   toFind  10  notFound   -1      for int i   0  i lt  sizeof arr   i             if arr i     toFind                  cout lt  lt   quot Element is found at  quot   lt  lt i  lt  lt  quot  index quot   lt  lt endl              return 0                         cout lt  lt notFound lt  lt endl

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Using Newton C    bool exists linear  INPUT ITERATOR first  INPUT ITERATOR last  const T amp  value    bool exists binary  INPUT ITERATOR first  INPUT ITERATOR last  const T amp  value     the code will be something like this   if   newton  exists linear arr begin    arr end    value       std  cout  lt  lt   found   lt  lt  std  endl  else    std  cout  lt  lt   not found   lt  lt  std  endl    both exists linear and exists binary use std implementations  binary use std  binary search  and linear use std  find  but return directly a bool  not an iterator

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One wants this to be done tersely  Nothing makes code more unreadable then spending 10 lines to achieve something elementary  In C    and other languages  we have all and any which help us to achieve terseness in this case  I want to check whether a function parameter is valid  meaning equal to one of a number of values  Naively and wrongly  I would first write  if   any of   DNS TYPE A  DNS TYPE MX    wtype  return false    a second attempt could be  if   any of   DNS TYPE A  DNS TYPE MX      amp wtype  const int elem    return elem    wtype      return false    Less incorrect  but looses some terseness  However  this is still not correct because C   insists in this case  and many others  that I specify both start and end iterators and cannot use the whole container as a default for both  So  in the end   const vector validvalues  DNS TYPE A  DNS TYPE MX    if   any of validvalues cbegin     validvalues cend      amp wtype  const int elem    return elem    wtype      return false    which sort of defeats the terseness  but I don t know a better alternative    Thank you for not pointing out that in the case of 2 values I could just have just if         The best approach here  if possible  is to use a case structure with a default where not only the values are checked  but also the appropriate actions are done  The default case can be used for signalling an invalid value

User · Answer

In C   you would use std  find  and check if the resultant pointer points to the end of the range  like this   Foo array 10          Init the array here Foo  foo   std  find std  begin array   std  end array   someObject      When the element is not found  std  find returns the end of the range if  foo    std  end array         cerr  lt  lt   Found at position    lt  lt  std  distance array  foo   lt  lt  endl    else       cerr  lt  lt   Not found   lt  lt  endl

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C   has NULL as well  often the same as 0  pointer to address 0x00000000    Do you use NULL or 0  zero  for pointers in C     So in C   that null check would be    if   foo      cout  lt  lt   not found

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Here is a simple generic C  11 function contains which works for both arrays and containers  using namespace std   template lt class C  typename T gt  bool contains C amp  amp  c  T e    return find begin c   end c   e     end c       Simple usage contains arr  el  is somewhat similar to in keyword semantics in Python  Here is a complete demo   include  lt algorithm gt   include  lt array gt   include  lt string gt   include  lt vector gt   include  lt iostream gt   template lt typename C  typename T gt  bool contains C amp  amp  c  T e         return std  find std  begin c   std  end c   e     std  end c       template lt typename C  typename T gt  void check C amp  amp  c  T e        std  cout  lt  lt  e  lt  lt   contains c e     quot  quot     quot  not quot    lt  lt    quot  found n quot      int main         int a       10  15  20        std  array lt int  3 gt  b   10  10  10        std  vector lt int gt  v   10  20  30        std  string s    quot Hello  Stack Overflow quot              check a  10       check b  15       check v  20       check s   Z         return 0     Output  10 found 15 not found 20 found Z not found

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