I want to reverse the string array result but when i run this code in online compiler it says "strrev was not declared". I don't understand this.
for(j=1;j<=test;j++)
{
cin >> input;
strcpy(result,input);
length = strlen(result);
strrev(result);
cout<<"Case "<<j<<": ";
for(i = 0;i<=length;i++)
{
if(result[i]==input[i])
p=0;
else
{
p=1;
break;
}
}
if(p==0)
cout<<"Yes"<<endl;
else
cout<<"No"<<endl;
}
Where does strrev come from? It's not part of the Standard library. You will have to include the header file that defines it, and include that.
You are using C++ (cout) so don't use char arrays and strlen, but use std::string instead. (You will need #include <string> at the top of your file)
for(int j=0;j<test;j++) // Life is easier if you get in the habit of writing loops like this
{
std::string input; // Don't declare variables until you need them.
std::cin >> input;
// Initialize 'result' as the reverse of input directly.
const std::string result(input.crbegin(), input.crend());
const char* const answer = (input == result) ? "Yes" : "No";
std::cout << "Case " << (j+1) << ": " answer << std::endl; // Offset test case for output.
}
You'll notice that my code is a LOT shorter than yours - I'm getting the library to do nearly all the heavy lifting. I've also avoided using namespace std. In the long term, it makes your code clearer if you leave it out.
I'm also tempted to write a function fromCin, which returns the string. Then I would write const std::string input = fromCin(); which has the lovely result that all my variables in the loop are constants.
Related
I've been trying to take a .txt document with three number entries, read those entries as strings and convert those entries in ints, then put them into an int array, but had no success in doing so and i have no clue as to why. Note that the entries as well as some variable names are pre determined by the assignment, additionally we have to use the std::stoi("string") command, which i am not familiar with nor has any syntax been provided to us (which is especially strange since we are usually not allowed to stray to far from the lecture material)
What I excpected to happen is that the numbers from the .txt file were converted into an array, however what actually happened is that an "unhandled exception" (my apologies if that term does not make sanes we have to programm in our native language) occured and the string library opened itself, marking the error on line 107. The problematic line in my code seems to be "auftraegearray[i++] = std::stoi(MengeanAuftraegen);"
int main()
{
std::fstream Auftraege;
Auftraege.open("Auftraege37.txt", std::ios::out);
Auftraege << "10" << std::endl;
Auftraege << "1" << std::endl;
Auftraege << "20" << std::endl;
Auftraege.close();
int i = 0;
int auftraegearray[4];
std::string MengeanAuftraegen;
Auftraege.open("Auftraege37.txt", std::ios::in);
while (!Auftraege.eof())
{
getline(Auftraege, MengeanAuftraegen);
std::cout << MengeanAuftraegen << std::endl;
auftraegearray[i++] = std::stoi(MengeanAuftraegen);
}
Auftraege.close();
Sorry to ask, but I been looking everywhere to find a way to extract the integers from this set of strings:
{(1,2),(1,5),(2,1),(2,3),(3,2),(3,4),(4,3),(4,5),(5,1),(5,4)}
I don't really need the homework done, if you could link me to an example, I'll appreciate it.
thank you in advanced.
If you just want to access the integers from a line like that, one way is to simply continue reading integers while you can.
If, for some reason, you find an integer read failing (because there's a { in the input stream, for example), just skip over that single character and keep going.
Sample code for this is:
#include <iostream>
int main() {
int intVal; // for getting int
char charVal; // for skipping chars
while (true) {
while (! (std::cin >> intVal)) { // while no integer available
std::cin.clear(); // clear fail bit and
if (! (std::cin >> charVal)) { // skip the offending char.
return 0; // if no char left, end of file.
}
}
std::cout << intVal << '\n'; // print int and carry on
}
return 0;
}
A transcript follows:
pax> echo '{(314159,271828),(42,-1)}' | ./testprog
314159
271828
42
-1
I've just started using boost in c++ and I just wanted to ask a couple of questions relating to uuids.
I am loading in a file which requires I know the uuids so I can link some objects together. For this reason, I'm trying to write my own uuids but I'm not sure if there's any special conditions for the strings etc as the strings I've been using (usually something basic) are not working. Can anyone point me in the right direction? I've tried using a string generator, but to no avail thus far so I'm assuming there's something wrong with my strings (which have currently just been random words).
Here's a short example kind of thing, can't give the real code:
void loadFiles(std::string xmlFile);
void linkObjects(custObj network)
{
for (int i = 0; i < network->getLength(); i++)
{
network[i]->setId([boost::uuid]);
if (i > 0)
network[i]->addObj(network[i-1]->getId());
}
}
I took your question as "I need a sample". Here's a sample that shows
reading
writing
generating
comparing
uuids with Boost Uuid.
#include <boost/uuid/uuid.hpp>
#include <boost/uuid/uuid_io.hpp>
#include <boost/uuid/random_generator.hpp>
#include <boost/lexical_cast.hpp>
using namespace boost::uuids;
int main()
{
random_generator gen;
for (int i = 0; i < 10; ++i)
{
uuid new_one = gen(); // here's how you generate one
std::cout << "You can just print it: " << new_one << "; ";
// or assign it to a string
std::string as_text = boost::lexical_cast<std::string>(new_one);
std::cout << "as_text: '" << as_text << "'\n";
// now, read it back in:
uuid roundtrip = boost::lexical_cast<uuid>(as_text);
assert(roundtrip == new_one);
}
}
See it Live On Coliru
I am getting all kinds of errors when passing my array to this function. The function is suppose to have the user enter a name and a score and store them in 2 seperate arrays, one for the names, one for the scores. I believe I have to use pointers but have no idea on how to use them. I don't want the answer, just a push in the right direction. Here is the code:
#include <iostream>
int InputData(int &, char, int);
using namespace std;
int main()
{
char playerName[100][20];
int score[100];
int numPlayers = 0;
InputData(numPlayers, playerName, score);
return 0;
}
int InputData(int &numPlayers, char playerName[][20], int score[])
{
while (numPlayers <= 100)
{
cout << "Enter Player Name (Q to quit): ";
cin.getline(playerName, 100, ‘\n’);
if ((playerName[numPlayers] = 'Q') || (playerName[numPlayers] = 'q'))
return 0;
cout << "Enter score for " << playerName[numPlayers] <<": ";
cin >> score[numPlayers];
numPlayers++;
}
}
Ok, I made some more changes and the errors are less, must be getting close, Lol!
This looks like a school assignment and I applaud you for not asking for the answer. There are several ways to do it, but you are already fairly close in the approach that you are using. When you pass an array reference, you do not want to include the length of the array. For example, the parameter int score[100] should be int score[]. The exception, especially in your scenario, is with multidimensional arrays. In this case, you want to use char playerName[][20]. Your function declaration also needs to change to match. Don't forget InputData returns an int. Your declarations and function call are correct; you just need to adjust your function signature.
Keeping the errors aside -
InputData(numPlayers, playerName, score, size);
// ^^^^ size is no where declared
// resulting Undeclared indentifier error
Prototype mentions of taking 3 arguments but calling the function passing 4 parameters.
Hint regarding errors:
An 1D array decays to a pointer pointing to first element in the array while passing to a function.
A 2D array decays to a pointer pointing to the 1D array ( i.e., T[][size] ) while passing to a function.
Return type of main() should be int.
It seems with the given hints you corrected most of the errors. But you forgot to change the prototype. So, change -
int InputData(int &, char, int);
to
int InputData(int &, char[][20], int[]);
Why aren't you using std::string array for player names ? Use it and remove rest of the errors. Good luck.
I have code such as this. I use
pvalueholder is class that is polymorphic , it can hold all sort of types, string..etc..
It also can have a type undefined.
typedef hash_map<pvalueholder,pvalueholder,pvaluehasher > hashtype;
hashtype h;
pvalueholder v;
v="c";
h[v]=5; // h has one element
pvalueholder v2=h[v]; // here h gets a new key/value how is that possible?
cout << (string) (h[v]) << endl; // here h gets another new key/value how is that possible?
int i =0;
for (hashtype::iterator h1=h.begin(); h1!=h.end();h1++)
{
cout << "no: " << i++ << endl;
} // this prints three lines, it should print one...
Two values are undefined here, the third one is 5 as expected.
size_t pvaluehasher::operator() (const pvalueholder& p) const
{
cout << "hashvalue:" << p.value->hashvalue() << endl;
return p.value->hashvalue();
}
returns
Here is what is printed:
hashvalue:84696444
hashvalue:84696444
hashvalue:84696444
returns:1
hashvalue:84696444
returns:1
hashvalue:84696444
returns:1
returns:1
hashvalue:84696444
Do you have any ideas what it may be?
Thank you.
Solution:
the function operator()(parameter1,parameter2) needs to be different in case of Microsoft STL.
For microsoft, it needs to return less than relationship between parameter1 and parameter2.
For gcc, it needs to return equality. I returned equality.
The comparison function for the keys was not correct...
The function returned true for equality while it has to return less than in case of Microsoft STL.
My guess would be that your hash function is incorrect - meaning it produces different hash values given the same key "c".
Show the declaration for pvalueholder and full code for pvaluehasher.
It's almost impossible to comment on hash_map, because it's never been standardized, and the existing implementations aren't entirely consistent. Worse, your code doesn't seem to be correct or compilable as it stands -- some places the value associated with the key seems to be an int, and other places a string.
Using std::tr1::unordered_map and fixing the rest of the code to compile and seem reasonable, like this:
#include <unordered_map>
#include <iostream>
#include <string>
using namespace std;
typedef std::tr1::unordered_map<std::string, int> hashtype;
std::ostream &operator<<(std::ostream &os, std::pair<std::string, int> const &d) {
return os << d.first << ": " << d.second;
}
int main() {
hashtype h;
std::string v = "c";
h[v]=5; // h has one element
int v2=h[v];
cout << h[v] << endl;
int i =0;
for (hashtype::iterator h1=h.begin(); h1!=h.end();h1++)
{
cout << *h1 << endl;
} // this prints three lines, it should print one...
return 0;
}
The output I get is:
5
c: 5
This seems quite reasonable -- we've inserted only one item, as expected.
Solution: the function operator()(parameter1,parameter2) needs to be different in case of Microsoft STL. For microsoft, it needs to return less than relationship between parameter1 and parameter2. For gcc, it needs to return equality. I returned equality. The comparison function for the keys was not correct... The function returned true for equality while it has to return less than in case of Microsoft STL.