Re: playing with vectors
"arnuld" <geek.arnuld@gmail.com> wrote in message
news:pan.2007.08.03.11.57.56.192993@gmail.com...
/* C++ Primer 4/e
* STATEMENT
* given 2 vectors of integers, write a programme to determine
whether one vector * is the prefix of the other vector e.g. if 1st vector
has elements (0,1,1,2) and 2nd * vecotr has elements (0,1,1,2,3,5,8) then
programme should say "TRUE" and if 2nd * vector is smaller then too it
should say "TRUE", else it should say "FALSE". *
*/
#include<iostream>
#include<vector>
int main()
{
std::vector<int> ivec1, ivec2;
int ival;
/* creation of 1st vector */
std::cout << "Enter elements for 1st vector" << std::endl;
while(std::cin >> ival)
{
ivec1.push_back(ival);
}
At this point std::cin is in a bad state.
std::cout << "1st vector is created with elements: ";
for(std::vector<int>::const_iterator iter=ivec1.begin();
iter != ivec1.end(); ++iter)
{
std::cout << *iter << " ";
}
std::cout << "\n-------------------" << std::endl;
/* creation od 2nd vector */
ival = 1; /* because ival had EOF value since used last time */
std::cout << "Now enter elements for 2nd vector" << std::endl;
while(std::cin >> ival)
std::cin is still in a bad state, so it won't accept any more input. You
have to reset std::cin
You should read the FAQ 15 entirely.
http://www.parashift.com/c++-faq-lite/input-output.html#faq-15 or at least
until 15.6
std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
should reset std::cin to a good state.
You'll want to
#include <limits>
{
ivec2.push_back(ival);
}
std::cout << "2st vector is created with elements: ";
for(std::vector<int>::const_iterator iter=ivec2.begin();
iter != ivec2.end(); ++iter)
{
std::cout << *iter << " ";
}
std::cout << std::endl << std::endl;
unsigned sizeSmaller;
int size1 = ivec1.size();
int size2 = ivec2.size();
/* this "if-else" clause will make the next "for" loop a generalise one
and the "else clause" will work even for vectors of same length */
if(size1 < size2)
{
sizeSmaller = size1;
}
else
{
sizeSmaller = size2;
}
bool prefix_test = true;
for(std::vector<int>::size_type ix=0;
(ix != sizeSmaller) && prefix_test;
++ix)
/* notice the test-condition:
1st, "ix" is an unsigned int and that is why we made sizeSmaller an
unsigned int. 2nd condition will break the loop as soon as we will
meet with 1st false test :) */
{
if(ivec1[ix] != ivec2[ix])
{
prefix_test = false;
}
}
/* print the result */
if(prefix_test)
{
std::cout << "--> TRUE" << std::endl;
}
else
{
std::cout << "--> FALSE" << std::endl;
}
return 0;
}
this programme compiles and runs but it has a semantic bug. i intended
that it will ask me to input elements for both vectors but it only askes
me to input elements for the 1st vector. it seems like the 2nd while loop
never runs. here is the ouput:
[arnuld@arch cpp] $ g++ -ansi -pedantic -Wall -Wextra ex_06-15.cpp
[arnuld@arch cpp] $ ./a.out
Enter elements for 1st vector
1
2
3
1st vector is created with elements: 1 2 3 -------------------
Now enter elements for 2nd vector
2st vector is created with elements:
--> TRUE
[arnuld@arch cpp] $
--
http://arnuld.blogspot.com