I got a task from my teacher. I try some code but it confuses me a lot. So here's my code :
#include <iostream>
using namespace std;
char inputChecker [1000];
string source = "10110111000111001101110";
string detected;
int main(){
cout <<"Input:";
cin >> inputChecker;
for (int i=0;i<source.size();i++){
if (source[i]==inputChecker[0]){
cout <<"Data " <<inputChecker <<"is exist" <<endl;
}
else if (source[i]==inputChecker[i]){
cout <<"Data " <<inputChecker <<" isn't exist'" <<endl;
}
}
}
So ,my expectation output is ,when i input 10,it will result "Data 10 is exist". Without looping. I think it needed 2 kind of looping but i dont know where to loop.
My expectation output :
Input : 10
Data 10 is exist
Input : 25
Data 25 isn't exist
Thanks in advance :))
No need for loop
#include <iostream>
using namespace std;
int main() {
string source = "10110111000111001101110";
string input;
cin >> input;
if (source.find(input) != string::npos)
cout << input << " exists\n";
else
cout << input <<" doesn't exist\n";
}
Have a look at other useful std::string methods like find_first_of, find_last_of, etc.
Related
I just started learning C++ and I'm currently following a tutorial on YouTube.
I thought it was fun to make a very simple 'access' program. If I type in my name it says, "Welcome!" If I type in another name it says, "access denied". It worked perfectly fine, but then I wanted the program to say "Welcome!" to two different names. So, I wanted to add a second name in the string, but I couldn't figure out how to do that. I googled a lot but I couldn't find anything. In the end, I came to string name = ("Joe", "Sean");, but here, it was only valid for Sean. I just can't figure out how to put multiple names in one string and make them both work. I hope you can help me, here is my code:
#include <iostream>
#include <cmath>
#include <string>
using namespace std;
int main()
{
string name = ("Joe", "Sean");
string input;
cout << "What is your name?\nMy name is: ";
cin >> input;
if(input == name){
cout << "Welcome, "<< input <<"! ";
} else {
cout << "Access denied";
}
return 0;
}
This is a way to do it using a vector of strings, so you can adapt easily with more names :
#include <iostream>
#include <vector>
using namespace std;
void printMessage(string message)
{
std::cout << message << std::endl;
}
int main()
{
vector<string> names{"Joe", "Sean", "Paul"};
string input;
cout << "What is your name? " << endl;
cin >> input;
for (string name : names)
{
if (name == input)
{
printMessage("Welcome!");
return 0;
}
}
printMessage("Access Denied!");
return 0;
}
The problem is in the string variable "name". You need an array of strings, not a single string.
This is an example implementation:
#include <iostream>
#include <cmath>
#include <string>
using namespace std;
int main()
{
string names[] = {"Joe", "Sean"};
string input;
cout << "What is your name?\nMy name is: ";
cin >> input;
for (int i = 0; i < end(names) - begin(names); i++) {
if(input == names[i]){
cout << "Welcome, "<< input <<"! " << endl;
return 0;
}
}
cout << "Access denied" << endl;
return 0;
}
You encountered some quirky features of C++ in the approach you are using to initialize your string variable:
string s1 = ("Joe"); // creates a string "Joe"
string s2 = ("Joe", "Sean"); // creates 2 strings, "Joe" and "Sean", and the variable s2 stores only the latter!
For more details on the different methods for initializing variables there has been an interesting discussion in this previous question.
I have been struggling with a certain error that doesn't make sense to me. Whenever I try to compile this program, it tells me that I'm missing a semicolon when I am not.
It seems the error is linked to a specific block of code, that being the if statement that checks stock. Since I know c++ can be platform specific, I'm running debian 9 and the atom ide if that's any help.
Here is the specifc error:
error: expected primary-expression before ',' token
getline(string,line);//gets string`
and the code:
#include <iostream>
#include <fstream>
using namespace std;
int main ()
{
cout << "store stocking system: \n"; // yadda yadda yadda UX
cout << "commands: \n";
cout << " help: shows available commands\n check stock: checks store stock\n enter stock: enter new stock items\n";
cout << " exit: terminates the program\n clean house: deletes all stock\n";
home: // main loop in program
string output;
output = ">> ";
cout << output;
string stock;
string item; // this whole block just defines things and gets input
int itemNumber;
string userInput;
getline(cin,userInput);
if (userInput == "exit")
{
return 0;
}
if (userInput == "enter stock")
{ // enters new stock
cout << "enter item\n>> "; //item name
cin >> item;
cout << "enter amount\n>> "; //amount of item
cin >> itemNumber;
ofstream myfile; //makes file
myfile.open("stock.txt"); //opens myfile
myfile << "\n" << item << "," << itemNumber << "\n"; //writes to file
myfile.close();// closes file
cout << "done";
goto home; //finishes and goes to main loop
}
if (userInput == "check stock") // where the problem is
{
string line;
ifstream file("stock.txt");//checks fo file
file.open("stock.txt");//opens file
getline(string,line);//gets string
file.close();//closes it
cout << line << "\n";
goto home;
}
if (userInput == ""){
goto home;
}
else
{
cout << "\033[1;31mplease use a proper command:\033[0m\n";
goto home;
}
return 0;
}
Are you missing this by any chance?
#include <string>
I believe it simply needs to be getline(file,line) rather than getline(string,line) and then you should be sorted.
string is recognized as a type name, of type std::string which you generously exposed by line using namespace std;. This particular error message is caused by fact that string isn't an expression which can be evaluated . In context of your code it should be
getline(file,line);
PS. Standard would say that you have to include <string> header to use component std::string. Your code compiles thanks to an implementation-defined feature, was imported with <iostream> in this version of header.
My goal is to prompt user to enter a message / sentence and then print it out on the screen, using getline(). The following is two different attempts I have tried out.
First Attempt:
#include <iostream>
#include <iomanip>
#include <cstring>
using namespace std;
int main(){
chat message[80];
cout << "\n what is your message today?" << endl;
cin.getline( message, 80); // Enter a line with a max of 79 characters.
if( strlen( message) > 0) // If string length is longer than 0.
{
for( int i=0; message[i] != '\0'; ++i)
cout << message[i] << ' ';
cout << endl;
}
}
Second Attempt:
#include <iostream>
#include <iomanip>
#include <cstring>
using namespace std;
int main(){
string a = "a string";
cout << "\n what is your message today?" << endl;
while(getline(cin,a))
cout << a;
cout<<endl
}
}
For the fist attempt, the code simply print out "what is your message today?" and quit. I do not have a chance to enter any string at all. For the second attempt, it keeps asking me enter the message. Each time, when I enter something with the "\n", it would display what I entered on the screen. I use control + c to interrupt the running process to make it stop.
EDIT: To clarify and explain on my side, I extract the first attempt from a longer code, which is as the following.
#include <iostream>
#include <iomanip>
#include <cstring>
using namespace std;
char header[] = "\n *** C Strings ***\n\n"; // define a c string
int main()
{
char hello[30] = "Hello ", name[20], message[80]; // define a c string hello, declare two other c strings name and message
string a="fivelength";
cout << header << "Your first name: ";
cin >> setw(20) >> name; // Enter a word.
strcat( hello, name); // Append the name.
cout << hello << endl;
cin.sync(); // No previous input.
cout << "\nWhat is the message for today?"
<< endl;
cin.getline( message, 80); // Enter a line with a max of 79 characters.
if( strlen( message) > 0) // If string length is longer than 0.
{
for( int i=0; message[i] != '\0'; ++i)
cout << message[i] << ' ';
cout << endl;
}
return 0;
}
For the above code, it does not give me a chance to enter a message on the screen. I will put it as another question.
You are overcomplicating this, you can simply use std::string, which is the de-facto C++ string, and call the method, without using a loop.
You don't need a loop, since you are not going to repeatedly read lines, but only want to read one line, so no loop is needed.
#include <iostream>
#include <string> // not cstring, which is the C string library
using namespace std;
int main(void)
{
string message; // it can be an empty string, no need to initialize it
cout << "What is your message today?" << endl;
getline(cin, message);
cout << message;
cout<<endl;
return 0;
}
Output (Input: "Hello Stack Overflow!"):
What is your message today?
Message: Hello Stack Overflow!
PS: As #fredLarson commented, if you change chat to char in your first example, it should work. However, that code has a lot of commonalities with C.
I'm a newbie with c++, and I tried googling a solution but every one I came across was so different from the issue I was facing so I couldn't figure it out. The problem I'm having is my "if" statements are completely ignored when I run the .exe from powershell.
https://pastebin.com/aE6MiQig
#include <iostream>
#include <string>
using namespace std;
int main()
{
string q;
string w;
string Bob;
string Emily;
{
cout << "Who is this? ";
cin >> q;
if (q == Bob)
{
cout << "Hey there bro. ";
}
if (q == Emily)
{
cout << "Hi friend :) ";
}
else
{
cout << "Oh hey " << q << ", how are you? ";
}
cin >> w;
cout << "Hey, that's " << w;
}
return 0;
}
When I input my name as "Bob" I should be seeing the message from the if statement "Hey there bro." but I am instead seeing the else statement, "Oh hey Bob, how are you?". Same goes when I input Emily. Only seeing the else statement.
I'm not getting any errors (running this in visual studio) so where am I messing this up?
Why not just compare directly to strings?
#include <iostream>
#include <string>
int main()
{
std::string q;
std::string w;
std::cout << "Who is this? ";
std::cin >> q;
if (q == "Bob") // note the quotation marks around Bob
{
std::cout << "Hey there bro. " << std::endl;
}
else if (q == "Emily") // note the quotation marks around Emily
{
std::cout << "Hi friend :) " << std::endl;
}
else
{
std::cout << "Oh hey " << q << ", how are you? ";
std::cin >> w;
std::cout << "Hey, that's " << w << std::endl;
}
return 0;
}
Also, you should avoid using namespace std because it leads to namespace pollution. Instead, you can just put std:: in front of string, cin, cout, and endl as I've done above, or include a using statement for each of those specifically, like this:
using std::string;
using std::cin;
using std::cout;
using std::endl;
std::string comes with its own operator==, comparing the string's contents.
string Bob;
string Emily;
Well, now you have created two strings, both using the default constructor, and so both are empty strings (i. e. they both would compare equal to "").
You need to assign them a value:
string Bob("Emily");
string Emily("Bob");
I deliberately assigned them inverse! Try this piece of code and you'll discover yourself that it is the content that is relevant for comparison, not the variable's name...
You obtain the value for string q from the user and compare it to string Emily or string Bob , neither of which have any values assigned.
The problem I'm having is my "if" statements are completely ignored when I run the .exe from powershell.
Your if statements are not being ignored instead you're comparing string q to "".
You can give string Bob and string Emily initial values:
#include <iostream>
#include <string>
int main()
{
std::string Bob = "Bob";
std::string Emily = "Emily";
std::string q;
}
This way you have something to compare the values you're getting from cin to:
#include <iostream>
#include <string>
int main()
{
std::string Bob = "Bob";
std::string Emily = "Emily";
std::string q;
std::cout<<"What is your name? ";
std::cin>>q; //Obtain value from cin
if(q == Emily){}//If q is Emily, then do something
}
You can read more about default variable values here and here.
I want to be able to loop this file opening and closing to continually search for names.
The first time is no problem and output is what is expected then, when choosing y for yes, an output loop occurs.
Any ideas as to why this would happen? The logic seems more than correct.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
string boys, girls, name;
int rank;
char end = 'n';
while (end != 'y' || end != 'Y')
{
cout << "Enter a name to search";
cin >> name;
ifstream input;
input.open("Names2016");
if (input.fail())
cout << "Failed to open file.\n";
while (!input.eof())
{
input >> rank >> boys >> girls;
if (boys == name)
cout << name << " ranks " << rank << " among boys.\n";
if (girls == name)
cout << name << " ranks " << rank << " among girls.\n";
}
input.close();
cout << "Would you like to search another name?\n"
<< "Enter Y for yes or N for no.\n";
cin >> end;
}
return 0;
}
There are a some of things you can do to make this code better,
The first is to use ifstreams and do file input/output the proper idiomatic way in a loop, don't use .eof() to check for end of file in a loop condition (the answer linked in the comments is a good place to start if you want to know why),
The second thing you want to check for validity of the file with a simple if (!file) its much cleaner IMO.
The third thing is, when you have a local file handle like you do in your code, then you can just let it go out of scope and let the destructor cleanup the file and close() it, it's the C++ RAII way of doing things (notice that I have removed the open() method to the constructor call (which does the same thing)
Use cerr instead of cout to report errors
Use char instead of int to represent characters
Not a big change, but using std::toupper like advised in the other answer's comments is a good readable way to check for uppercase and lowercase values at the same time
#include <iostream>
#include <fstream>
#include <string>
#include <cctype>
using namespace std;
int main()
{
string boys, girls, name;
int rank;
char end = 'n';
while (std::toupper(end) == 'Y')
{
cout << "Enter a name to search";
cin >> name;
ifstream input{"Names2016"};
// change here
if (!input) {
cerr << "Failed to open file.\n";
}
while (input >> rank >> boys >> girls)
{
if (boys == name)
cout << name << " ranks " << rank << " among boys.\n";
if (girls == name)
cout << name << " ranks " << rank << " among girls.\n";
}
// change below, just let the file handle go out of scope and close
// input.close();
cout << "Would you like to search another name?\n"
<< "Enter Y for yes or N for no.\n";
cin >> end;
}
return 0;
}
But you can do better on the I/O if your file isn't guaranteed to change over different iterations (in which case you probably need to make sure that there is no race anyway, so I am assuming the file does not change much). Read in the file once and save that information to be used later
#include <iostream>
#include <fstream>
#include <string>
#include <cctype>
#include <unordered_map>
#include <vector>
using namespace std;
int main()
{
string boys_name, girls_name, name;
int rank;
char end = 'n';
ifstream input{"Names2016"};
if (!input) {
cerr << "Failed to open file" << endl;
}
// preprocess the information and store it in a map
// making a map from string to vector because it is unclear whether
// there is a 1-1 mapping from the name to the rank for each name
unordered_map<string, vector<int>> boys;
unordered_map<string, vector<int>> girls;
while (input >> rank >> boys_name >> girls_name) {
boys[boys_name].push_back(rank);
girls[girls_name].push_back(rank);
}
while (std::toupper(end) == 'Y')
{
cout << "Enter a name to search";
cin >> name;
// use the map to do the lookup, much faster than reading
// the entire file over and over again
}
return 0;
}
First of all, what is this supposed to mean int end = 'n'; Are you assigning an integer with a character value?!
And why are you opening the same file inside the loop. You should probably open it only once at the beginning of the program.
And the eof doesn't have what to check for, because you have to read from a file to reach its end.