So this is my main method:
#include <iostream>
#include "TextFileToArray.h"
#include <vector>
using namespace std;
int main()
{
cout << "Hello world!" << endl;
TextFileToArray myobject("C:/bunz.txt");
vector<string> v[10];
myobject.vectorfiller(*v);
for(int i =0; i<10; i++){
cout << v;
}
}
It calls upon an object known as myobject and it calls upon a method/function. Here is the method/function:
int TextFileToArray::vectorfiller(vector<string>& givenpointer) {
vector<string> *innervec = &givenpointer;
const char * constantcharversion = path.c_str();
ifstream filler(constantcharversion);
string bunz;
string lineoutliner = "Line ";
string equalssign = " = ";
int numbercounter = 1;
while (!filler.eof()) {
std::getline(filler, bunz, ';');
if (bunz.empty()) {
lineoutliner = "";
numbercounter = 0;
equalssign = "";
}
cout << lineoutliner << numbercounter << equalssign << bunz <<endl;
cout << "" << endl;
innervec->push_back(bunz);
numbercounter++;
}
filler.close();
return 0;
}
So far it displays the text from the textfile, but for some reason it pushes memory addresses into the vector, so when main() displays the vector, it shows memory locations:
vector<string> v[10]; creates an array of 10 vectors, which is probably not what you want.
Create a single vector, pass that as parameter, and output its contents:
vector<string> v;
myobject.vectorfiller(v);
for(int i =0; i < v.size(); i++){
cout << v[i];
}
Agree, size should not be 10, should be size(), and count<
The problem is that you're printing the array of vectors, not the elements in the first vector. Instead, you want this in your main:
for (int i = 0; i < v[0].size(); i++) {
cout << v[0][i] << endl;
}
PS: As Luchian said, you are creating 10 vectors, not one vector with 10 slots. To get just one vector do this:
vector<string> v;
You also don't need to mention 10; vectors grow when you push elements on them. If you happen to know how much space you want to be reserved ahead of time, you can use the reserve member function like so:
vector<string> v;
v.reserve(some_number);
reserve doesn't change the size of v; it only makes the vector ready to accept that many elements, so that it doesn't have to reallocate memory, and copy things around as much. It is purely an optimization; if you were to simply comment out reserve calls in your program, it will behave exactly the same. The only thing that might change is performance, and memory usage.
Related
This kind of explains it all I really don't know why this is happening, can you guys help? I even made the length constant because I though that could be the problem, but it still happens so I really don't know.
So the problem is that I define length1 as 4, but then after a few times in the for loop, the value just randomly changes...
#include <iostream>
#include <string>
using namespace std;
int uppercase[26] = {65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90};
int lowercase[26] = {97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122};
string test;
int entered_text[] = {};
int length = 0;
int length1 = 0;
int main() {
cout << "Enter Text:" << endl;
getline (cin, test);
length = test.size();
length1 = 4;
cout << test<< endl;
for (int i = 0; i < length1; i++){
entered_text[i] = test[i];
}
cout << entered_text[0] << endl;
return 0;
}
By looking at your code, it seems you're approaching this problem as if you were coding in JavaScript and using objects. Obviously, C++ does not approach objects the same way as JavaScript (nowhere near the same).
Here is a rough example of what you could do instead. I don't understand what you're trying to do, but I believe you can implement dynamic arrays and pointers to tackle the problem you have. Read up on using C++ pointers and C++ dynamic arrays. Here is some "rough" code that will hopefully get you on your way:
int main() {
cout << "Enter Text:" << endl;
getline (cin, test);
cout << test<< endl;
length = test.size();
// Create dynamic array and have this array the size of your string.
// Also, initialize a pointer to point to the address of your new array
int *enteredText;
enteredText = new char [length];
int *save = enteredText;
// Iterate over the array “entered_text” and assign it values
for (int i = 0; i < length; i++){
*entered_text = test[i];
entered_text++;
}
// now print chars
for (int i = 0; i < length; i++){
cout << *save << endl;
save++;
}
return 0;
don't make every variable you use global, its better to keep them local if there's no strong reason to do otherwise, and in c++ you have to tell your compiler the size of your array, or use allocation, but I would suggest to use std::vector<int>
My goal is to try and create a program that takes in grades in percents and multiply it with their weight value (either in decimal form or percent form). The equation is basically:
Overall grade = (grade1*weightInDecimal1)+(grade2*weightInDecimal2)+(grade3*weightInDecimal3)+...
or
Overall grade = (grade1*weight%1)+(grade2*weight%2)+(grade3*weight%3)+...
Is there a way to store the inputs and then recall it later in the code? Or possibly a more efficient way?
I also want to try and make a dynamic array. I want to make a program that asks the user for how many assignments they have and makes an array based on that. That way it's not stuck at 4 assignments
#include <string>
#include <iostream>
using namespace std;
int main() {
int numbers[4][2];
for(int i=0;i<4;i++)
{
cout<<"Grade #"<<i<<endl;
cin>>numbers[i][0];
cout<<"Weight for grade #"<<i<<":"<<endl;
cin>>numbers[i][1];
}
for (int i = 0; i<4; i++)
{
cout << "|" << numbers[i][0]*numbers[i][1]<< "|";
}
system ("PAUSE");
return 0;
}
This is what structs are for
#include <string>
#include <iostream>
#include <array>
using namespace std;
struct entry {
int grade;
int weight;
int gradeWeight; //grade*weight
};
int main() {
array<entry,4> numbers;
for(int i=0;i<numbers.max_size();i++)
{
cout<<"Grade #"<<i<<endl;
cin>>numbers[i].grade;
cout<<"Weight for grade #"<<i<<":"<<endl;
cin>>numbers[i].weight;
}
for (int i = 0; i<numbers.max_size(); i++)
{
numbers[i].gradeWeight = numbers[i].grade*numbers[i].weight;
cout << "|" << numbers[i].gradeWeight << "|";
}
system ("PAUSE");
return 0;
}
This way you can also increase the amount of numbers by just increasing the array size.
As pointed by others, if you ask the user for how many assignments they have, std::array is a wrong container because it's dimension is fixed at compile time.
As others, I discurage the use of direct memory allocation but the use of std::vector to manage it.
I just suggest the use of reserve() (method of std::vector), when you know how many assignments.
The following is a full example using, instead a couple of std::vector of int, a single std::vector of std::pair<int, int>
#include <utility>
#include <vector>
#include <iostream>
int main()
{
int valG, valW;
std::size_t dim;
std::vector<std::pair<int, int>> vec;
std::cout << "How many grade/weight couples? ";
std::cin >> dim;
vec.reserve(dim);
for ( auto i = 0U ; i < dim ; ++i )
{
std::cout << "Grade #" << i << "? " << std::endl;
std::cin >> valG;
std::cout << "Weight for grade #" << i << "? " << std::endl;
std::cin >> valW;
vec.emplace_back(valG, valW);
}
for ( auto const & p : vec )
std::cout << '|' << (p.first * p.second) << '|';
std::cout << std::endl;
return 0;
}
There are many reasons to avoid using arrays (dynamic or otherwise). See for example Stroustrup's FAQ entry What's wrong with arrays? As Greg suggests in the comments you will most likely write better quality code if you use a container like std::vector.
If you can calculate or input the size of your container before allocating it you can (if you wish) pass that size to the constructor ...
auto syze{ 0 };
auto initialValue{ 0 };
// calculate or input syze
. . .
// dynamically allocate an "array"
// of ints and an "array" of floats
std::vector<int> grades(syze, initialValue);
std::vector<float> weights(syze, initialValue);
On the other hand if you prefer to use a container that dynamically grows to hold data as it arrives you can do that too...
// dynamically allocate an empty "array"
// of ints and an empty "array" of floats
std::vector<int> grades;
std::vector<float> weights;
while (...condition...)
{
std::cin >> g; // input a grade ...
std::cin >> w; // ... and a weight
// grow the containers by adding
// one item at the end of each
grades.emplace_back(g);
weights.emplace_back(w);
}
Update
I should have pointed out how to calculate the result from the two vectors. You can calculate your overall grade with just one more line of code by using std::inner_product from the STL's <numeric> header. Note that in the code below the last argument is 0.0 (rather than just 0) so that std::inner_product returns a double rather than an int. That avoids any risk of float values being truncated to int (and avoids some pretty ugly warnings from the compiler).
auto overallGrade = std::inner_product(grades.begin(), grades.end(), weights.begin(), 0.0);
I'm doing some exercises with vectors. I created a function that fill a vector with defined size but when I tried to make it n size, the vector apparently is filled with trash memory, it shows: 0x23fe20, and my code crash when I try to use the vector.
#include <iostream>
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
using namespace std;
int cargavn(int vec[]) // fill vector
{
int i, t;
cout << "vector size: ";
cin >> t;
for(i = 0 ; i <= t-1; i++)
{
cout << "v["<< i <<"]=";
cin >> vec[i];
}
return (1);
}
int main()
{
int vec[10]; // the vector, size here wont matter
cargavn(vec); // call fill vector n positions
cout << vec; // to test if the vector is well filled
system("PAUSE");
}
you are exprecting cout << vec to somehow pretty print the vector. It wont, it just prints its address
You need to loop over the contents and print each element
for(int i =0 ; i < 10 ; i++)
{
cout << vec[i];
}
Here's how it would look using modern C++:
#include <iostream>
#include <vector>
using namespace std;
void cargavn(vector<int> &vec)
{
int t;
cout << "vector size: ";
cin >> t;
for(int i = 0; t > 0; ++i, --t)
{
cout << "v["<< i <<"]=";
int v;
cin >> v;
vec.push_back(v);
}
}
ostream &operator<<(ostream &s, vector<int> const &vec)
{
s << '{';
bool first = true;
for (int v : vec)
{
if (!first)
{
s << ", ";
}
s << v;
first = false;
}
return s << '}';
}
int main()
{
vector<int> vec;
cargavn(vec);
cout << vec;
system("PAUSE");
return 0;
}
Things to understand about this version compared to yours:
Unnecessary includes are ommitted.
Prefer C++ containers like vector over C style arrays.
Use dynamically sized containers when they need to hold an arbitrary number of values provided by the user instead of fixed-size containers that break when the user enters too much data. See the rule of 0, 1, infinity.
When all control paths of a function return the same value, then the returned value is pointless and can be omitted. Particularly if none of the callers even bothers to check the return value. I suspect you had the intention of using the return value to indicate some kind of unexpected error. This is a C-style approach to error handling. C++ uses exceptions to deal with unexpected errors.
Overload operator<< to extend the stream insertion operator to decide how containers and your own custom types should be formatted. The standard library doesn't provide any such insertion operator for vector because there isn't any universally agreed upon way to decide how a vector of values should be formatted. So you decide this for yourself.
It is good form for main to return a value, even though this is not technically required.
I am trying to use a function to sort through a char array full of words. The current issue I am having is that in my sortNames function I am getting the error, "expression must be a modifiable lvalue" at the part below
hold = nameArr[ii];
nameArr[ii] = nameArr[jj];
nameArr[jj] = hold;
I am guessing that its because I am trying to pass values through an array for some reason. I am struggling with understanding references and pointers and the such, and I imagine that is hurting me here as well. Any help with this would be fantastic, thank you in advance.
Here is my current code...
#include <iostream>
#include <string>
using namespace std;
char nameArr[20][15]; // array to store the 20 values
int val = 0; // variable to pass values to the array
int x = 0; // loop counter outside functions
//Function prototypes
void getNames(char (&nameArr)[20][15], int &val);
void sortNames( char(&nameArr)[20][15]);
//getNames Function
void getNames(char (&nameArr)[20][15], int &val)
{
int i = 0; // loop counter
cout << "Awesome, now lets input those names...\n" << endl;
for (i = 0; i < val; i++)
{
cout << "\nNAME " << i+1 << ": " << ' ';
cin >> nameArr[i];
}
cout << "\n\n\nThese are the names that you inserted:\n" << endl;
for (i = 0; i < val; i++)
{
cout << nameArr[i] << "\n" << endl;
}
}
// sortNames function
void sortNames( char(&nameArr)[20][15])
{
int n = 15; // max length of word
int ii = 0; // loop counter
int jj = 0; // other counter
string hold; // holding array
for (int ii = 0 ; ii < n ; ii++)
{
for (int jj = ii + 1; jj < n; jj++)
{
if (nameArr[ii] > nameArr[jj])
{
hold = nameArr[ii];
nameArr[ii] = nameArr[jj];
nameArr[jj] = hold;
}
}
}
}
int main()
{
cout << "NAME SORTER!\n\nPlease enter in the amount of names you wish to enter: " << ' ';
cin >> val;
getNames(nameArr, val);
cout << "\n\n\nAlright, lets sort now..." << endl;
sortNames(nameArr);
cout << "\nHere are the results:\n" << endl;
for (x = 0; x < val; x++)
{
cout << nameArr[x] << "\n" << endl;
}
system("pause");
}
Your main problem here is that you are trying to use an assignment operator on two fixed sized arrays, which isn't legal. Consider the following code:
int a[2] = {0, 0};
int b[2] = {1, 1};
a = b;
This gives the same error you are getting. On the lines you mentioned, you are doing the same thing with char[15] arrays.
To fix your problems, you either need to allocate your char array dynamically/work with the pointers, or a simpler solution would be to just change your char[][] array to a string[] array.
That being said, there are a lot of things you can clean up here:
You have a few variables declared globally that can just be defined in main or lower
You can declare loop counters inside the for loop instead of beforehand, as you do in the sortNames function
In sortNames you are declaring a few variables twice
I'll add a few things to dwcanilla's answer.
You will want to change your function prototypes and headers to something more like this:
void getNames(char ** & arr, int val);
void sortNames(char ** & arr);
What this means is that the function accepts a reference to an array of c-strings; that is, when you work with the array within the function you are modifying the actual array you passed and not just a copy. Also I think you'd be fine just passing the integer by value for getNames.
Second, global variables are generally a bad idea. Since you can pass the array reference directly to your functions you may want to declare nameArr and your other global variables inside main instead.
Third, in getNames you won't be able to use cin to assign your c-strings directly.
EDIT: This is a better way --
getting console input for Cstrings
Finally, the < operator doesn't work on c-strings the way you're using it in your sort function. Use strcmp() instead (and be sure to include the cstring header):
if(strcmp(arr[ii], arr[jj]) > 0)
I was practicing on c++ on some tutorials and I encountered on a tutorial that creates matrices, I wanted something more from it and I modified it, I dont know matrices at all cuz I didnt learn them yet at school but this code below sometimes works sometimes not.
When it doesn't work I usually get: Segmentation fault.
why does this happen ?
before it happened everytime but after i gave a 0 value to variable line and member on the beginning it doesnt happen anymore, but still if I type exc
Line: 10
Member: 9
it gives:
1 1 1 1 1 1 1 1 1
1 2 3 4 5 1 7 8 9
Segmentation fault
and stopes.
Can anyone explain me this ?
thank you !
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
int line=0,member=0;
int i,j,matrice[line][member];
cout << "\nLine: ";
cin >> line;
cout << "Member: ";
cin >> member;
cout << "\nCreated Matrice: \n" << endl;
for (i=0;i<line;i++)
{
for (j=0;j<member;j++)
{
matrice[i][j]=i*j+1;
cout << setw(5) << matrice[i][j];
}
cout << "\n\n";
}
return 0;
}
int line=0,member=0;
int i,j,matrice[line][member];
This line shouldn't compile. In standard C++,
arrays of 0 size are not allowed
array sizes must be constant expressions
It appears that your compiler allows these as extensions. In any case when you later input line and member your array size doesn't change. You should define your array after you've input these numbers. But the array must be dynamically allocated (better yet, use vectors)
#include <vector>
//...
int line, member;
cin >> line >> member;
vector<vector<int> > matrix(line, vector<int>(member));
or if you don't want to use vector for educational purposes, do this:
int line, member;
int ** matrix;
cin >> line >> member;
matrix = new int*[line];
for(int i = 0; i < line; ++i)
matrix[i] = new int[member];
Don't forget to free the matrix.
for(int i = 0; i < line; ++i)
delete [] matrix[i];
delete [] matrix;
I suggest that you should read a good C++ book
HTH
The matrice array is initialized with a size of [0][0], which are the values of line and member. Since you override the values with the inputted values, the bounds used in the for loops are invalid.
i.e. You are accessing items out of the array's bounds.
You may want to use new to dynamically create arrays, or just use std::vector which resizes itself.
Also, it is not standard, but if your compiler supports it, you can use variable-length arrays. They behave like regular arrays but are allocated using a runtime-computed value :
int line=0,member=0;
int i,j;
cout << "\nLine: ";
cin >> line;
cout << "Member: ";
cin >> member;
int matrice[line][member];
You should also check for the inputted values, since C++ does not allows zero-size arrays (And it wouldn't make sense in your program anyway.)
You are using dynamic array without allocating memory using malloc or similar. That is in your line int i,j,matrice[line][member]; is not an array with constant size thus memory should be dynamically allocated. Or use a constant matix size as poster above suggested.
I agree with other comments that using vectors is a much safer way to solve your problem: using arrays directly is definitely error-prone. Of course, if your exercise requires using arrays, then you should use arrays.
Regarding the performance, I have written a small test using g++ on Ubuntu 10.04. Running
g++ --version
I get
g++ (Ubuntu 4.4.3-4ubuntu5) 4.4.3
My test program creates a 100x100 matrix and sets each element to some value. It first has a few declarations:
#include <vector>
#include <iostream>
#include "util.h" // Timer utilities.
#define LINE_COUNT (100) // The number of lines.
#define COL_COUNT (100) // The number of columns.
#define REPETITIONS (100000) // Number of repetitions for each test.
using namespace std;
Then I have the test using vectors:
void use_vectors()
{
int line = LINE_COUNT;
int member = COL_COUNT;
vector<vector<int> > matrix(line, vector<int>(member));
// Set data.
for (int i = 0; i < line; i++)
{
for (int j = 0; j < member; j++)
{
matrix[i][j] = -5;
}
}
}
Then I have a function to perform the same test (create matrix and set values) using arrays:
void use_arrays()
{
int line = LINE_COUNT;
int member = COL_COUNT;
int **matrix;
matrix = new int * [line];
for (int i = 0; i < line; i++)
{
matrix[i] = new int[member];
}
// Set data.
for (int i = 0; i < line; i++)
{
for (int j = 0; j < member; j++)
{
matrix[i][j] = -5;
}
}
for (int i = 0; i < line; ++i)
{
delete [] matrix[i];
}
delete [] matrix;
}
The main program repeats both tests, and records the time needed for each of them. Here is the main program:
main()
{
long int es = 0;
long int eu = 0;
start_timer();
for (int i = 0; i < REPETITIONS; i++)
{
use_vectors();
}
stop_timer();
es = elapsed_sec();
eu = elapsed_usec();
cout << "Vectors needed: " << es << " sec, " << eu << " usec" << endl;
start_timer();
for (int i = 0; i < REPETITIONS; i++)
{
use_arrays();
}
stop_timer();
es = elapsed_sec();
eu = elapsed_usec();
cout << "Arrays needed: " << es << " sec, " << eu << " usec" << endl;
}
The timer functions are based on the library function gettimeofday() (see e.g. http://linux.die.net/man/2/gettimeofday).
The result is the following:
Vectors needed: 24 sec, 624416 usec
Arrays needed: 10 sec, 16970 usec
So it seems that vectors do have some overhead wrt to arrays. Or can I do something to improve the performance of vectors? I checked my benchmark code a few times and it seems to me I got it right.
Anyway, I would by no means advise using arrays just to gain performance unless it really makes a big difference in your application.
You want to allocate memory dynamically.
Then, Use Dynamic allocation like this:
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
int line=0,member=0;
int i,j;
int **matrice; //Define matrice as a 2D array(a Matrix)
cout << "\nLine: ";
cin >> line;
cout << "Member: ";
cin >> member;
//start of dynamic allocation
matrice=new int*[line];
for (i=0;i<line;i++)
matrice[i]=new int[member];
//End of dynamic allocation
cout << "\nCreated Matrice: \n" << endl;
for (i=0;i<line;i++)
{
for (j=0;j<member;j++)
{
matrice[i][j]=i*j+1;
cout << setw(5) << matrice[i][j];
}
cout << "\n\n";
}
delete[] matrice; //Releasing allocated memory
return 0;
}