How to cin to a vector

Question

I m trying to ask the user to enter numbers that are put into a vector  then using a function call to count the numbers  why is this not working   I am only able to count the first number   template  lt typename T gt  void write vector const vector lt T gt  amp  V       cout  lt  lt   The numbers in the vector are     lt  lt  endl    for int i 0  i  lt  V size    i        cout  lt  lt  V i   lt  lt          int main       int input    vector lt int gt  V    cout  lt  lt   Enter your numbers to be evaluated     lt  lt  endl    cin  gt  gt  input    V push back input     write vector V     return 0

User · Answer

would be easier if you specify the size of vector by taking an input    int main       int input n    vector lt int gt  V    cout lt  lt  Enter the number of inputs       cin gt  gt n    cout  lt  lt   Enter your numbers to be evaluated     lt  lt  endl    for int i 0 i lt n i       cin  gt  gt  input    V push back input         write vector V     return 0

User · Answer

You need a loop for that  So do this   while  cin  gt  gt  input    enter any non-integer to end the loop       V push back input       Or use this idiomatic version    include  lt iterator gt    for std  istream iterator   std  istream iterator lt int gt  begin std  cin   end  std  vector lt int gt  v begin  end   write vector v     You could also improve your write vector as     include  lt algorithm gt    for std  copy  template  lt typename T gt  void write vector const vector lt T gt  amp  v       cout  lt  lt   The numbers in the vector are     lt  lt  endl     std  copy v begin    v end    std  ostream iterator lt int gt  std  cout

User · Answer

include lt bits stdc   h gt  using namespace std   int main     int x n  cin gt  gt x  vector lt int gt  v   cout lt  lt  Enter numbers  n    for int i 0 i lt x i         cin gt  gt n    v push back n          displaying vector contents   for int p   v   cout lt  lt p lt  lt          A simple way to take input in vector

User · Answer

In this case your while loop will look like    int i   0  int a   0  while  i  lt  n     cin  gt  gt  a    V push back a       i

User · Answer

include lt iostream gt   include lt vector gt   include lt sstream gt  using namespace std   int main         vector lt string gt  v      string line t      getline cin line       istringstream iss line       while iss gt  gt t          v push back t        vector lt string gt   iterator it      for it v begin   it  v end   it            cout lt  lt  it lt  lt endl      return 0

User · Answer

You can simply do this with the help of for loop - Ask on runtime from a user   how many inputs he want to enter  and the treat same like arrays   int main             int sizz input          std  vector lt int gt  vc1           cout lt  lt   How many Numbers you want to enter              cin  gt  gt  sizz          cout  lt  lt   Input Data      lt  lt  endl          for  int i   0  i  lt  sizz  i       for taking input form the user             cin  gt  gt  input              vc1 push back input                     cout  lt  lt   print data of vector      lt  lt  endl          for  int i   0  i  lt  sizz  i                  cout  lt  lt  vc1 i   lt  lt  endl

User · Answer

If you know the size of the vector you can do it like this    include  lt bits stdc   h gt  using namespace std   int main         int n      cin  gt  gt  n      vector lt int gt  v n       for  auto  amp it   v            cin  gt  gt  it

User · Answer

Other answers would have you disallow a particular number  or tell the user to enter something non-numeric in order to terminate input  Perhaps a better solution is to use std  getline   to read a line of input  then use std  istringstream to read all of the numbers from that line into the vector    include  lt iostream gt   include  lt sstream gt   include  lt vector gt   int main int argc  char   argv         std  string line      int number      std  vector lt int gt  numbers       std  cout  lt  lt   Enter numbers separated by spaces         std  getline std  cin  line       std  istringstream stream line       while  stream  gt  gt  number          numbers push back number        write vector numbers        Also  your write vector   implementation can be replaced with a more idiomatic call to the std  copy   algorithm to copy the elements to an std  ostream iterator to std  cout    include  lt algorithm gt   include  lt iterator gt   template lt class T gt  void write vector const std  vector lt T gt  amp  vector        std  cout  lt  lt   Numbers you entered         std  copy vector begin    vector end            std  ostream iterator lt T gt  std  cout             std  cout  lt  lt    n       You can also use std  copy   and a couple of handy iterators to get the values into the vector without an explicit loop   std  copy std  istream iterator lt int gt  stream       std  istream iterator lt int gt         std  back inserter numbers      But that   s probably overkill

User · Answer

cin is delimited on space  so if you try to cin  1 2 3 4 5  into a single integer  your only going to be assigning 1 to the integer  a better option is to wrap your input and push back in a loop  and have it test for a sentinel value  and on that sentinel value  call your write function  such as  int input  cout  lt  lt   Enter your numbers to be evaluated  and 10000 to quit     lt  lt  endl  while input    10000        cin  gt  gt  input     V push back input     write vector V

User · Answer

These were two methods I tried  Both are fine to use  int main                     int size temp          cin gt  gt size          vector lt int gt  ar size         method 1        for auto i 0 i lt size i                  cin gt  gt temp                ar insert ar begin   i temp                         for  auto i ar               cout  lt  lt i lt  lt  quot   quot                        method 2      for int i 0 i lt size i                   cin gt  gt ar i                     for  auto i ar               cout  lt  lt i lt  lt  quot   quot            return 0

User · Answer

I ran into a similar problem and this is how I did it  Using  amp modifying your code appropriately     int main           int input     vector lt int gt  V     cout  lt  lt   quot Enter your numbers to be evaluated   quot       lt  lt    n   lt  lt   quot type  quot done quot   amp  keyboard Enter to stop entry quot       lt  lt      n      while    cin  gt  gt  input   amp  amp  input     quot done quot        V push back input            write vector V      return 0

User · Answer

You probably want to read in more numbers  not only one  For this  you need a loop  int main       int input   0    while input    -1       vector lt int gt  V      cout  lt  lt   Enter your numbers to be evaluated     lt  lt  endl      cin  gt  gt  input      V push back input       write vector V         return 0      Note  with this version  it is not possible to add the number -1 as it is the  end signal   Type numbers as long as you like  it will be aborted when you type -1

User · Answer

Just add another variable   int temp  while  cin  gt  gt  temp  amp  amp  V size    lt  n       V push back temp

User · Answer

you have 2 options   If you know the size of vector will be  in your case example it s seems you know it    vector lt int gt  V size  for int i  0 i lt size i         cin gt  gt V i        if you don t and you can t get it in you r program flow then   int helper  while cin gt  gt helper       V push back helper

User · Answer

The initial size   of V will be 0  while int n contains any random value because you don t initialize it    V size    lt  n is probably false   Silly me missed the  Enter the amount of numbers you want to evaluate     If you enter a n that s smaller than V size   at that time  the loop will terminate

User · Answer

include lt iostream gt   include lt vector gt   include lt string gt  using namespace std  int main         vector lt string gt V      int num      cin gt  gt num      string input      while  cin gt  gt input  amp  amp  num    0    enter any non-integer to end the loop          cin gt  gt input     V push back input      num--     if num  0          vector lt string gt   iterator it      for it V begin   it  V end   it            cout lt  lt  it lt  lt endl           return 0

User · Answer

One-liner to read a fixed amount of numbers into a vector  C  11     include  lt algorithm gt   include  lt iterator gt   include  lt iostream gt   include  lt vector gt   include  lt cstddef gt   int main         const std  size t LIMIT 5       std  vector lt int gt  collection       std  generate n std  back inserter collection   LIMIT                                     return   std  istream iterator lt int gt  std  cin                          return 0

User · Answer

If you know the size use this  No temporary variable used just to store user input  int main         cout  lt  lt   Hello World  n        int n   input size     cin  gt  gt  n      vector lt int gt a n       for  int i   0  i  lt  n  i              cin  gt  gt  a i            to verify output user input printed below      for  auto x   a            cout  lt  lt  x  lt  lt                 return 0

User · Answer

As is  you re only reading in a single integer and pushing it into your vector  Since you probably want to store several integers  you need a loop  E g   replace  cin  gt  gt  input  V push back input     with  while  cin  gt  gt  input      V push back input     What this does is continually pull in ints from cin for as long as there is input to grab  the loop continues until cin finds EOF or tries to input a non-integer value  The alternative is to use a sentinel value  though this prevents you from actually inputting that value  Ex   while   cin  gt  gt  input   amp  amp  input    9999      V push back input     will read until you try to input 9999  or any of the other states that render cin invalid   at which point the loop will terminate

User · Answer

You need a second integer   int i n  vector lt int gt  V  cout  lt  lt   Enter the amount of numbers you want to evaluate     cin  gt  gt  i  cout  lt  lt   Enter your numbers to be evaluated     lt  lt  endl  while  V size    lt  i  amp  amp  cin  gt  gt  n     V push back n     write vector V   return 0

[c++] How to cin to a vector

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