I'm new to C++.
In a part of a simple project, I have to enter a number and verify that it is positive and not an alphanumeric sequence. With the following code I perform the "check for alphanumeric sequence" but in which way I can add the "positive check"?
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
string getline()
{
string str;
getline(cin, str);
return str;
}
int main()
{
int choice;
istringstream iss(getline());
iss >> choice >> ws;
if(iss.fail() || !iss.eof())
{
cout << "Error" << endl;
}
}
Thank you in advance!!
Related
I am working on a project where I have to parse data from user input.
#include <iostream> // for cin and cout
#include <iomanip> // for setw()
#include <cctype> // for toupper()
using namespace std;
int main(){
string playerInput;
cin >> playerInput;
//Player would input strings like C13,C 6, I1, Z 16, etc...
}
return 0;
I've tried something like this, which kinda works but only if the letter proceeds the number in the string.
int myNr = std::stoi(playerInput);
What my end goal is to grab the letter and number from the string, and place them in a char variable and a integer variable respectively. I am stuck on how to proceed from here and could use some help, thanks!
This is the simplest and the shortest way to achieve that (it also ignores spaces and tabs):
int main() {
char ch;
int n;
cin >> ch >> n;
cout << "ch = " << ch << ", n = " << n << endl;
}
I think that other answers are a bit overcomplicated.
You could do like what you had:
char letter = playerInput.front();
playerInput.erase(0);
int number = std::stoi(playerInput);
Of course, that doesn't allow for spaces. Removing spaces can be quite tedious, but it could be done like:
playerInput.erase(
std::remove_if(
begin(playerInput), end(playerInput),
[](uint8_t ch) { return std::isspace(ch); }),
end(playerInput));
Full Demo
Live On Coliru
#include <cctype> // for toupper()
#include <iomanip> // for setw()
#include <iostream> // for cin and cout
#include <algorithm> // for remove_if
static bool ignorable(uint8_t ch) {
return std::isspace(ch)
|| std::ispunct(ch);
}
int main() {
std::string playerInput;
while (getline(std::cin, playerInput)) {
playerInput.erase(
std::remove_if(
begin(playerInput), end(playerInput),
ignorable),
end(playerInput));
if (playerInput.empty())
continue;
char letter = playerInput.front();
playerInput.erase(begin(playerInput));
int number = std::stoi(playerInput);
std::cout << "Got: " << letter << " with " << number << "\n";
}
}
Prints
Got: C with 13
Got: C with 6
Got: I with 1
Got: Z with 16
You have the right idea in using std::stoi. My code expands your approach:
string playerInput;
getline(cin, playerInput);
char c1 = playerInput[0];
int num = stoi(playerInput.substr(1));
The above code receives an input string, then takes out the first character and uses std::stoi on the rest of the string.
Note that I use std::getline to account for the possibility of there being spaces in the input. If you are doing this repeatedly, you will need to add cin.ignore() after each getline() statement. See this link for more info.
std::cin stops reading input when it encounters a space. You can use std::getline() if your input has spaces. To parse your string, you should check out std::stringstream. It allows you to read from a string as if it were a stream like std::cin.
#include <iostream> // for cin and cout
#include <iomanip> // for setw()
#include <cctype> // for toupper()
#include <sstream>
int main(){
std::string playerInput;
int i;
char c;
std::getline(std::cin, playerInput); // Remove trailing newline
std::getline(std::cin, playerInput);
//Player would input strings like C13,C 6, I1, Z 16, etc...
//String Stream
std::stringstream playerInputStream(playerInput);
//Read as if you were reading through cin
playerInputStream >> c; //
playerInputStream >> i;
}
return 0;
I'll say first that sending my code a hardcoded, perfectly formatted string works fine. But when letting user input string, the code parses areaCode but fails during exchange parsing. Here is my .h
// PhoneNumber.h
#ifndef PHONENUMBER_H
#define PHONENUMBER_H
#include <string>
class PhoneNumber {
private:
short areaCode;
short exchange;
short line;
public:
PhoneNumber(std::string number);
void setPhoneNumber(std::string number);
std::string getPhoneNumber() const;
void printPhoneNumber() const;
};
#endif
Here is my .cpp implementation
// PhoneNumber.cpp
#include <iostream>
#include <iomanip>
#include <string>
#include <sstream>
#include <cctype>
#include <stdexcept>
#include "PhoneNumber.h"
PhoneNumber::PhoneNumber(std::string number) {
setPhoneNumber(number);
}
void PhoneNumber::setPhoneNumber(std::string number) {
int length = number.length();
std::istringstream iss(number);
int count = 0;
while (!isdigit(number[count])) {
count += 1;
iss.ignore(1);
}
iss >> std::setw(3) >> areaCode;
count += 3;
while (!isdigit(number[count])) {
count += 1;
iss.ignore(1);
}
iss >> std::setw(3) >> exchange;
count += 3;
while (!isdigit(number[count])) {
count += 1;
iss.ignore(1);
}
if (length - count < 4) {
throw std::invalid_argument("Something wrong with your phone number input");
}
else {
iss >> std::setw(4) >> line;
}
}
void PhoneNumber::printPhoneNumber() const {
std::cout << "(" << areaCode << ") " << exchange << "-" << line;
}
And now my short test code.
// PhoneNumber testing
#include <iostream>
#include <string>
#include "PhoneNumber.h"
int main() {
std::string p1;
std::cout << "Enter phone number in format of (800) 555-1212: ";
std::cin >> p1;
PhoneNumber phone1(p1);
phone1.printPhoneNumber();
std::cout << std::endl;
}
I have tried to write my setPhoneNumber code so that it is user error tolerant. So first question is how do I make this work with user input? Secondary (need not be answered) why does it work with hardcoded telephone number string and not user input?
std::cin >> p1;
will only read to the first space or carriage return. So, if the user inputs (800) 555-0123, you'll only read "(800)".
You need
std::getline(std::cin, p1);
to read the input.
The reason it works with a hardcoded string is that the string assignment operator is not affected by this. When you code p1 = "(800) 555-0123";, p1 gets set to "(800) 555-0123"
I want the user to enter the name of a file, and if the file exists, print out all the contents of the file.
At the moment the uncommented code, takes a name of a file that the user inputs, for example. example.txt and prints out most (not the last word?) of the file. I've tried to implement this instead by using string (commented code is attempt) but clearly its incorrect.
I also wondering if i can automatically add .txt to the end of the user input, so that the console could ask - "which subject should we find more information on" user inputs "math" and it will open "math.txt"
Here is what I´ve tried:
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <string>
using namespace std;
int main() {
char filename[50];
//string getcontent;
ifstream name;
cin.getline(filename, 50);
name.open(filename);
if (!name.is_open()) {
exit(EXIT_FAILURE);
}
char word[50];
name >> word;
while (name.good()) {
cout << word << " ";
name >> word;
}
//if (!name.is_open()) {
//while (! filename).eof())
//{
//getline(name, getcontent)
//cout << getcontent << endl;
//}
//exit(EXIT_FAILURE); //comes from cstdlib
//}
//}
system("pause");
return 0;
}
#include <iostream>
#include <fstream>
#include <cstdlib>
#include <string>
using namespace std;
int main() {
string filename;
string getcontent;
ifstream name;
cin >> filename;
filename.append(".txt"); // add extension.
name.open(filename);
if (!name.is_open()) {
exit(EXIT_FAILURE);
}
while (true)
{
getline(name, getcontent);
if (name.eof()) break;
cout << getcontent << endl;
}
return 0;
}
I found this and it helped me with a somewhat different problem and I also thought that I might be able to help. This is coded in windows. (I'm a beginner so forgive me if I made some obvious mistakes)
#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;
ifstream fin;
int main()
{
//char filename[50],word[50];
string filename,word;
//cin.getline(filename,50);
getline(cin,filename);
//strcat(filename,".txt");
filename.append(".txt");
fin.open(filename);
if(fin.is_open())
while(fin>>word)
cout<<word<<endl;
else
cout<<"No such file"<<endl;
return 0;
}
I'm not able to figure out why the loop in following program is not running exactly testCount times. Please help to make it correct.
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main() {
size_t testCount;
cin >> testCount;
if(testCount < 0 || testCount > 100) return 0;
int input;
while(testCount--) {
string instr;
getline(cin,instr);
istringstream iss(instr);
while(iss >> input) {
cout << input << endl;
}
}
return 0;
}
Thanks. I got it. The problem is with getline(). First loop cycle is getting wasted as getline() is taking first line containing just new line character when I pressed enter key after typing testCount value.
std::ws is an input stream manipulator which ignores all whitespaces to the point where the first non-whitespace character is encountered.
Also, getline leaves whitespaces where they are if they don't fit in the line. cin >> ws will discard those.
Here's the bullet proof code:
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main() {
size_t testCount;
cin >> testCount >> ws;
if(testCount < 0 || testCount > 100) return 0;
int input;
while(testCount--) {
cout << "testCount " << testCount << endl;
string instr;
cin >> ws;
getline(cin,instr);
istringstream iss(instr);
while(iss >> input) {
cout << input << endl;
}
}
return 0;
}
So Lets say this is what the input file contains
12
Hello
45
54
100
Cheese
23
How would I print it out on the screen in that order.
This is what I had but it skips some lines.
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
int number;
string word;
int loop = 0;
ifstream infile;
infile.open("arraynumbers.txt");
while(infile >> number >> word)
{
if( infile >> number)
{
cout << number << endl;
}
if(infile >> word)
{
cout << word << endl;
}
}
return 0;
}
I suggest using www.cplusplus.com to answer these questions.
However, you are on the right track. Since you are just outputting the contents of the file to stdout, I suggest using readline() and a string. If you need to access the numeric strings as ints, use the atoi() function.
Example:
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
string line;
ifstream file("arraynumber.txt");
if (file.is_open()) {
while (getline(file, line)) {
cout << line << endl;
}
file.close();
} else cout << "Error opening arraynumber.txt: File not found in current directory\n";
return 0;