Wouldn'tpbuk said:
break instead of continue also exit the loop cleanly in your example?cout << "the first key was: " << userSelection
<< ", the ASCII is " << int(userSelection) << endl;int ascii = 97;, then cout << char(ascii) displays a.Thanks for the program. I think I understand, I just want to confirm one thing.pbuk said:
No, that's not quite right. First of all the code you write does not read into a buffer, this part is done by the operating system. Also,yungman said:
cin is actually a line input buffer cin.get which is why you have to hit enter, rather than a keyboard buffer which reads keys straight away.cin.get(userSelection) waits for a character to appear in the keyboard line input buffer (which will only happen after return has been entered) and then reads one character from the buffer into userSelection which is passed by reference.Does it look like this code reads anything from any input buffer?yungman said:
Yes it would, but breaking out of ajtbell said:
while(true) loop is not a very understandable way to write code. Putting the termination condition up front makes it much easier to see when you want the loop to terminate.Yes this is the way I would normally do it but the OP used two variables so I kept to that. Note that you can also cast usingjtbell said:
(int) userSelection which the compiler treats exactly the same way; I prefer this because int(userSelection) looks like a function call. Note also that when you do ascii = userSelection the compiler is performing an implicit cast. With certain compiler settings, userSelection = ascii will report a warning, @yungman can you think why?And of course yourpbuk said:
cin.ignore() ensures that, if you enter more than one character before pressing 'return', the program processes only the first one and skips over the rest.cin.ignore(), recompile, run, and then enter a word instead of a single character and see what happens.I am sorry, I can't really understand what you are saying. If you want to work out how it works the best thing is just to play with it.yungman said:
Correct, you won't see anything from cin until you hit enter.yungman said:
As many characters as you have typed before hitting enter are in the buffer - it could be 0, 1 or many - as well as the \n (i.e. ENTER) character.yungman said:
Only if it was there - if the first and only character was \n then the buffer is now empty.yungman said:
Nowhere in either your code or mine is one cin.get() followed by another.yungman said:
Not exactly. In order for the buffer to be read, two conditions must be satisfied:yungman said:
char type so it reads exactly one byte from the buffer. If you have only typed \n, that is what you will get and the buffer will be empty so if you immediately try to flush it your program will wait around for another character to flush. That's why I checked straight away to see if ENTER was the character received from the buffer.Yes, I wrote a program with words reading in last name and first, then print out, then as to hit ENTER to quit or any other character to do it again:jtbell said:
// enter multiple data in one cin
#include <iostream>
using namespace std;
int main()
{
char LastName[21] = { '\n' }, FirstName[21] = { '\n' };
char userSelection = 'A';
do
{
cout << endl;
cout << "Enter LastName and FirstName with a space in between, then hit ENTER "<< "\n";
cin >> LastName >> FirstName;
cout << "\n";
cout << "You entered " << LastName << " " << FirstName << endl;
cout << "\n";
cin.ignore(255, '\n');// clear ENTER
cout << " Hit any character to repeat, hit ENTER to quit ";
cout << endl;
cin.get(userSelection);
} while (userSelection != '\n');
return 0;
}std::string. And insted of using cin >>, you use the std::getline() function, which reads from an input stream (e.g. cin) until it encounters a newline. The chars up to (but not including) the newline go into the string, and the newline is discarded. To test whether the user simply pressed <return>, you test the string to see if it's empty.#include <iostream>
#include <string>
int main ()
{
std::string choice = "go";
while (choice != "")
{
std::cout << "Enter a character, or <return> to exit: ";
std::getline (std::cin, choice);
std::cout << "You entered '" << choice << "'." << std::endl;
if (choice != "")
{
std::cout << "'" << choice[0] << "'"
<< " has the ASCII code " << int(choice[0]) << "."
<< std::endl;
}
}
return 0;
}No, there is no problem with reading a newline character from an input stream as you can see from my code in #278(!). The problem with @yungman's code was that after reading one character (which could be a newline) he was callingjtbell said:
ignore() which was waiting around for another newline.Yes,jtbell said:
std::getline() is generally more useful than cin >>. But actually neither of these are very useful - interactive console programs aren't really a thing in C++; if I were @yungman I'd drop it and move on.// Read and write to file
#include<iostream>
#include<fstream>
using namespace std;
int main()
{
ofstream outputFile;
outputFile.open("demofile.txt");
cout << "Now writing data to the demofile.txt" << endl;
outputFile << "Bach\n";
outputFile << "Beethoven\n";
outputFile << "Mozart\n";
outputFile << "Schubert\n";
outputFile.close();
cout << "Done " << endl;
cout << endl;
return 0;
}I don't understand, it is a new file as you see created by the program named "demofile.txt". It only contain 4 words( 4 names). It is less than 50 characters if you count them all including the name of the file.sysprog said:
Please look at the file name in the error message ##-## it's between quotation marks, and it's about 100 characters long. The file name that the message is reporting is the VS-generated name of a debug file. The fully-qualified name includes the path name, which includes everything in the directory structure from the drive letter to the most deeply nested current subdirectory. It also includes the whole of your project name, which lengthily describes the program, instead of just being something like P002. You can also rename directories to something shorter, e.g. abbreviate Microsoft to MS, and Visual Studio to VS. The full path character string from drive letter to current subdirectory doesn't appear in the message, so I can't see all the reductions you could do to reduce its length.yungman said:
I think I copied it correctly here:sysprog said:
It's a good idea to create descriptive names for your projects, but not good to go overboard on the names. I have several hundred projects that I've created over the years, but they're short with no spaces, to remind me what the basic purpose of the program is. Instead of "3.29 read write to file ifstream ofstream open close," I would have called the project "FileOutput."yungman said:
What you describe may or may not be strange. The only other C/C++ compiler I've used was Borland's product, close to 30 years ago.yungman said:
{
ofstream outputFile;
outputFile.open( C:\Users\alanr\Desktop\Alan amp3\SS\OPS\MOSFET\demofile.txt);
}You need double quotes around the path and filename string, and because characters preceded by a backslash (\) are escaped, you need to double them up.yungman said:
outputFile.open( "C:\\Users\\alanr\\Desktop\\Alan amp3\\SS\\OPS\\MOSFET\\demofile.txt");outputFile.open( "C:/Users/alanr/Desktop/Alan amp3/SS/OPS/MOSFET/demofile.txt");// Read and write to file
#include<iostream>
#include<fstream>
using namespace std;
int main()
{
ofstream outputFile;
outputFile.open("C:\Users\alanr\Desktop\C++ exercise\Gaddis\inout files\demofile.txt");
cout << "Now writing data to the demofile.txt" << endl;
outputFile << "Bach\n";
outputFile << "Beethoven\n";
outputFile << "Mozart\n";
outputFile << "Schubert\n";
outputFile.close();
cout << "Done " << endl;
cout << endl;
return 0;
}I explained why it doesn't work in post #303. Please read more carefully the posts where members are trying to help you out.yungman said:
Thanks, got it.Mark44 said:
Here's a different version of what you were trying to do, written purely in C. It usesyungman said:
_getche(), whose declaration is in conio.h. It gets a character from the keyboard, and echoes it to the screen. A slightly different function, _getch(), doesn't echo the character.#include <cstdio> // for printf()
#include <conio.h> // for _getche()
#define CR 13 // <ENTER> key
int main()
{
int userEntry;
do
{
printf("Press any key: ");
userEntry = _getche();
printf("\nYou hit: ");
if (userEntry == CR) printf("<ENTER>\n");
else printf("%c\n", (char) userEntry);
printf("ASCII code: %d\n", userEntry);
} while (userEntry != CR);
}Win uses CR and LF, while *n*x uses LF only, and assumes CR.Mark44 said:
Your string for the filename is broken. You have two options:yungman said:
Already stated in post #303.Timo said:
Mark44 said:
. I actually introduced a bug into our software yesterday that was totally avoidable if I had read the comment around line 4000 (of 27k) in the file I was editing.// setw() setprecision() and fixed do while
#include <iostream>
#include <iomanip>
using namespace std;
int main()
{
double doubleValue = 91.0;
cout << "Enter a double number "; cin >> setw(2)>> doubleValue; cout << endl; cout << endl;
cout << "(" << setw(6)<< setprecision(4) << doubleValue << ")" << endl; cout << endl;
return 0;
}Although the setw() and setprecision() manipulators work with both output streams and input streams, they are most often used to format output streams. This VS documentation -- https://docs.microsoft.com/en-us/cpp/standard-library/input-stream-manipulators?view=vs-2019 -- (with emphasis added) says this.yungman said:
setw() specifies the width of the display field for the next element in the stream. The ios_base class has flags that can be used to left-justify the thing being displayed, or right-justify it, convert lowercase characters to uppercase, display the thing in decimal, hex, or octal, and some othersyungman said: