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I'm new to time complexity in algorithms.
This is the code for counting the number of words in a text file.
My problem is that every time my program prints one more than the actual count of words in the file, like if I have 11 words in my file it prints 12.
#include<fstream>
#include<iostream>
#include<string>
using namespace std;
/* main function */
void main()
{
ifstream inFile; //file file name
string fileName;
string word;
int count = 0;
inFile.open("example.txt");
while(!inFile.eof())
{
inFile >> word;
++count;
}
cout << "Number of words in file is " << count<<endl;
inFile.close();
}
//this file is for counting the number of words in a text file**
First thing first : Why is iostream::eof inside a loop condition considered wrong? This will answer your extra count problem.
Then, coming to complexity, since it will go though every N words till it reaches end of file, it will be done in O( N ) time
Also, void main() is not legal c++, main should return int
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I'm sick and tired of solving why my ch[0] is of value "Thomas EdisonÇ#", when it should be "Thomas Edison"
int main(){
using namespace std;
ifstream in("U2.txt");
int n;
in>>n; //n=rows, so in every line there will be "name surname", time, money
char ch[n][21]; //I'm trying to get Name+Surname which must be 20 char long
in.read(ch[0], 20);
cout << ch[0]; //but getting Thomas EdisonÇ#
return 0;}
It works on one dimentional ch[21], but there's gonna be lots of values so I want to use ch[n][21]
Any other out of my box solution is welcome, I'm tired
You are forgetting that C strings need to be nul terminated
in.read(ch[0], 20);
ch[0][20] = '\0'; // add the nul terminator
cout << ch[0]; // now correct output
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I need to organize infinite loop with symbol analysis in it. In C I used fgets(buf, N, stdin), suppose buf is buf[10]. User could type string of any length and I could analyze it by breaking down the input and examining parts of length 10. How can I implement this in C++ without using C libraries. Sorry for my English if you can't understand what I mean
In C++ you should std::cin to read from standard input.
// #include <iostream>
do
{
char buf[10]{}; // create array of 10 bytes filled with zeros.
std::cin.read(buf, 10); // read 10 bytes
// at this point you should check if std::cin.read succeeded.
// otherwise you will be reading zeros.
std::streamsize numRead = std::cin.gcount(); // obtain number of read bytes.
std::cout << numRead << " " << buf << std::endl; // some printing.
}while(std::cin);
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I have read these two questions already:
Remove spaces from std::string in C++
remove whitespace in std::string
For some reason, I can never get the solutions to work correctly. In my program, I collect input from the user and pass it to an std::string. From there, I want to remove all of the spaces in it. For example, if the user inputs "3 + 2", I would like it to change to "3+2".
What happens is, whatever is before the first string is kept. Here is my program:
#include <iostream>
std::string GetUserInput() {
std::cout << "Please enter what you would like to calculate: ";
std::string UserInput;
std::cin >> UserInput;
return UserInput;
}
int PerformCalculation(std::string Input) {
Input.erase(std::remove_if(Input.begin(), Input.end(), ::isspace), Input.end());
std::cout << Input;
return 0;
}
int main() {
std::string CalculationToBePerformed = GetUserInput();
int Solution = PerformCalculation(CalculationToBePerformed);
return 0;
}
So when I run this program and type in "3 + 2", the output is "3".
Here is my console:
Please enter what you would like to calculate: 3 + 2
3
Process finished with exit code 0
I cannot figure out how to resolve this. I even tried using a solution that involved using a regex to remove all the \s characters, and that gave me the same issue.
To read the complete line (up to terminating \n), you need to use e.g. std::getline(std::cin, UserInput);. Otherwise, you're currently reading text up to first whitespace character.
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I'm trying to get the number 001 from the string UID001 (The user will always enter "UIDnnn"). I tried using cin.get and cin.ignore with delimiters but with no results. What is the most effective way to extract the integers from a string?
Well, the simplest c++ standard compliant solution seems to be as mentioned in my comment.
Read the ID value as a std:string:
std::string ID;
std::cin >> ID;
Get the substring with the number part:
std::string numpart = ID.substr(3);
Convert it to a numerical value:
int idnum = std::stoi(numpart);
This is one of those places that scanf and company really work well:
scanf("UID%d", &number);
With iostreams it's a bit uglier, but I'd consider something like:
for (int i=0; i<3; i++) {
char ch;
cin.get(ch);
}
cin >> number;
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A user had posted a similar question earlier this day which was very soon closed due to its vagueness. Thus re-posting the question in detail with a solution as I didn't find a specific article dealing with it on the internet.
The requirement is to read and print all lines of a file except the last K.
Suppose a file contains text as:
Hello there!
My name is
Mr. XYZ
I like playing football
And if K is 2, then it should print all the lines except the last 2. i.e.:
Hello there!
My name is
Why not simply put lines into a std::deque and dump one element when its size is greater k ?
#include<iostream>
#include<fstream>
#include<deque>
int main()
{
std::fstream fs;
fs.open("output.txt",std::ios::in);
std::deque<std::string> deq;
std::string str;
int k=2;
while(std::getline(fs,str))
{
deq.push_back(str);
if(deq.size() > k)
{
std::cout <<deq.front()<<std::endl;
deq.pop_front();
}
}
}
This can easily be solved by creating a window of size K and then traversing the file till the right end of the window reaches the end of the file. The basic steps being:
Traverse the first K lines of the file without printing it.
Open the same file using another stream object.
Now simultaneously traverse both the streams so that fisrt stream is always K lines ahead of the second stream.
Run a loop while the second first stream is valid. In the loop, read through the first stream as well and keep print the lines.
The code would be
#include<iostream>
#include<fstream>
#include<string>
int main()
{
fstream fs;
fs.open("abc.txt",ios::in);
string str;
int K = 2;
while(getline(fs,str) && K>1)
{
K--;
}
if(K==1)
{
fstream fsNew;
fsNew.open("abc.txt",ios::in);
while(getline(fs,str))
{
getline(fsNew,str);
cout<<str;
}
}
cin.ignore();
}