I am struggling to find a way to break down an input from the user to a location on a chess board. For example (A1). I want to make sure that they have entered a Letter between A and H and a number between 1 and 8. Not sure if comparing ASCII is the best approach?
Using C++ this is a snippet of what I have attempted. startingp is the input from the user
char startChar = startingp[0];
int SCascii = startChar;
int startInt = startingp[1];
if (!(ascii_A <= SCascii >= ascii_H) || !(1 <= startInt >= 8))
{
cout << "Your inputted move, " << startPos << ", is invalid." << endl;
cout << "Enter the coordinates of the piece you want to move. (eg A1) : ";
cin >> startingp;
cout << endl;
}
This condition:
(ascii_A <= SCascii >= ascii_H)
is not correct. Or at least, I don't think it's what you mean. Instead, do:
((ascii_A <= SCascii) && (SCascii >= ascii_H))
Other than that, your logic seems reasonable.
I made a Chess game as well, and this is what I used to get the coordinates:
Position* Interface::askPosition()
{
cout << "position: ";
string inp;
cin >> inp;
while (!(isalpha(inp[0]) && isdigit(inp[1]))) {
cout << "Please press CHAR + DIGIT\n";
cin >> inp;
}
return new Position(inp[0] - 'A', inp[1] - '1');
}
It's a static method of a class called Interface and returned a pointer to a Position object. However, this might be not a C++-clean way
You can just compare it with characters, no need to convert it into an int (ASCII).
char startChar = startingp[0];
int SCascii = startChar;
int startInt = startingp[1];
if (!(startChar>='A' && startChar<='H') || !(startInt>=1 && startInt<=8))
{
cout << "Your inputted move, " << startPos << ", is invalid." << endl;
cout << "Enter the coordinates of the piece you want to move. (eg A1) : ";
cin >> startingp;
cout << endl;
}
Related
I am a rookie coder here and I can't seem to figure out what to add to my code here to get it right. It is supposed to ask the user again if they do not answer the question "Do you want to make another calculation Y or N?" correctly. I want it to repetitively ask the user to enter y or n if they enter something else. I feel like it is obvious I am just missing it. This is for school, to be clear.
I've tried nesting a do while loop and an if statement but only to get run time errors
#include <iostream>
using namespace std;
int main() {
int base, exponent;
long int result = 1;
char choice;
int i;
do
{
cout << "This program raises a number to a specific power." << endl;
cout << "\nEnter a base integer greater than 1: ";
cin >> base;
cout << "\nEnter an exponent integer to raise that number to: ";
cin >> exponent;
for (i = 1; i <= exponent; i++)
{
result = result * base;
}
cout << "\n" << base << " to the power of " << exponent << " = " << result << endl;
result = 1;
// ***** HERE IS WHERE I NEED HELP, WHAT TO
// DO IF THEY DONT ENTER Y OR N.....
cout << "\nWould you like to make another calculation? Y or N: ";
cin >> choice;
cout << endl;
}
while (choice == 'y' || choice == 'Y');
cout << "Good bye, then. Have a good day.\n" << endl;
return 0;
}
When I tried adding a nested do while loop, and entered a character answer other than y or n, it would go to a part of the program it should not have.
*this is my first question so I hope I've done this correctly
You can use another do-while loop to wrap the input section.
do
{
cout << "This program raises a number to a specific power." << endl;
cout << "\nEnter a base integer greater than 1: ";
cin >> base;
cout << "\nEnter an exponent integer to raise that number to: ";
cin >> exponent;
for (i = 1; i <= exponent; i++)
{
result = result * base;
}
cout << "\n" << base << " to the power of " << exponent << " = " << result << endl;
result = 1;
do
{
cout << "\nWould you like to make another calculation? Y or N: ";
cin >> choice;
cout << endl;
} while (choice != 'y' && choice != 'Y' && choice != 'n' && choice != 'N');
}
while (choice == 'y' || choice == 'Y');
Learn to think organically here. Let me do a procedural approach.
We begin by bringing your formulations into a more technical form, until it is syntactically and semantically working. Let's start by transforming it into this:
void process_things()
{
...
while(still_require_answer)
{
ask_for_answer();
}
...
}
This is very close to how you formulate it verbally, yes? Now, let's flesh it out.
string ask_for_answer(bool& still_require_answer);
void process_things()
{
...
string answer = "";
bool still_require_answer = true;
while(still_require_answer)
{
answer = ask_for_answer(still_require_answer);
}
...
}
// hope you understand the concept of a reference here,
// that is what the ampersand (&) does, if not, ask
string ask_for_answer(bool& still_require_answer)
{
string answer = ""; // always initialize
cout << "State answer: ";
cin >> answer;
cout << endl;
if(answer == "Y" or ...)
{
still_require_answer = false;
}
return answer;
}
Hope this helps you. In the long run, you might want to go OOP and use classes here. The code here is a little bit verbose, but orderly.
Note that I have put the routine in a new function process_things. Anything that is more than a few lines which you can name you should think about making a function (or a class method). Your main should be quite small. Cutting things down into smaller units helps you keeping thisng orderly and makes the design of each single unit easy (divide-and-conquer) and allows you to quicker locate problems as you can test every function separately (later, this leads to automated unit tests).
One could also take the while and put it into it's own function string ask_until_valid_answer();, and if we do that, dissolve ask_for_answer and put it's content there. What I want to focus on is to have it organically, that is use self-descriptive names which explain the program while reading it, and to cut the program into understandable units. Here would be this other layout:
string ask_until_valid_answer();
void process_things()
{
...
string answer = ask_until_valid_answer();
...
}
string ask_until_valid_answer()
{
string answer = "";
bool still_require_answer = true;
while(still_require_answer)
{
cout << "State answer: ";
cin >> answer;
cout << endl;
if(answer == "Y" or ...)
{
still_require_answer = false;
}
}
return answer;
}
This is a program that grade user inputs for the questions of Driver's License Exam.
I'm having trouble of validating the user input.
I'd like to accept the [ENTER] key as an invalid input and proceed to my validation rather than just go to an empty line and cannot process to the next question. Purpose is to send out error message and that no input is given and [ENTER] key is not valid input and only accept one more chance to enter valid input which are a/A, b/B, c/C, or d/D. So that is why I'm using if statement here instead of loop.
I tried if (testTakerAnswers[ans] == (or =) '\n') {} but still doesn't solve the problem of newline.
I include curses.h in here hope to use getch() statement from the other post but somehow I can't manage to work in my code with an array instead of regular input.
I'm looking for other methods as well rather than getch()
So should I adjust my bool function, or directly validate input in main() function.
#include <iostream>
#include <iomanip>
#include <string>
#include <cctype>
#include <curses.h>
using namespace std;
const unsigned SIZE = 20; // Number of qns in the test
char testTakerAnswers[SIZE]; //Array to hold test taker's answers
bool validateInput(char);
class TestGrader
{
private:
char answers[SIZE]; // Holds the correct answers // Answer is array
int getNumWrong (char[]);
void missedQuestions (char[]);
public:
void setKey(string); // Initialize object with standard keys
void grade(char[]); // Grades the answers from tester
};
void TestGrader::setKey(string key){
if (key.length()!=SIZE){
cout << "Error in key data.\n";
return;
}
for (unsigned pos = 0; pos < SIZE ; pos ++)
answers [pos] = key [pos];
}
void TestGrader::grade(char test[])
{
int numWrong = getNumWrong(test);
if (numWrong <= 5)
cout << "Congratulations. You passed the exam.\n";
else
cout << "You did not pass the exam. \n";
cout << "You got " << (SIZE-numWrong) << " questions correct. \n";
if (numWrong > 0){
cout << "You missed the following " << numWrong << " questions: \n";
missedQuestions(test);
}
}
int TestGrader::getNumWrong(char test[])
{
int counter = 0;
for (int i = 0; i < SIZE; i++){
if (answers[i] != toupper(testTakerAnswers[i])){
counter++;
}
}
return counter;
}
void TestGrader::missedQuestions(char test[])
{
// cout << testTakerAnswers[i]; This is to print taker's answers
int counter = 0;
for (int i = 0; i < SIZE; i++){
if (answers[i] != toupper(testTakerAnswers[i])){
cout << "\n" << i + 1 << ". Correct answers: " << answers[i];
counter++;
}
}
}
bool validateInput(char ans){ // Only A, B, C, D valid input
if (toupper(ans)!='A' && toupper(ans)!= 'B' && toupper(ans)!='C' && toupper(ans)!= 'D'){
cout << "\n********************WARNING*******************\n";
cout << "Invalid input! Enter only a/A, b/B, c/C, or d/D\n";
return false;
}
if (testTakerAnswers[ans] == '\n'){
return false;
}
return true;
}
int main()
{
const int NUM_QUESTIONS = 20;
string name; //Test taker's name
char doAnother; //Control variable for main processing loop
TestGrader DMVexam; //Create a TestGrader object
DMVexam.setKey("BDAACABACDBCDADCCBDA");
do {
cout << "Applicant Name: ";
getline(cin,name);
cout << "Enter answer for " << name << ".\n";
cout << "Use only letters a/A, b/B, c/C, and d/D. \n\n";
for (int i = 0; i < NUM_QUESTIONS; i++){
// Input and validate it
do{
cout << "Q" << i+1 << ": ";
cin >> testTakerAnswers[i];
if (!validateInput(testTakerAnswers[i])){
cout << "You get one more chance to correct.\nOtherwise, it count as wrong answer.";
cout << "\n*********************************************";
cout << "\nRe-enter: ";
cin >> testTakerAnswers[i];
cout << '\n';
break;
}
}while(!validateInput(testTakerAnswers[i]));
}
//Call class function to grade the exam
cout << "Results for " << name << '\n';
DMVexam.grade(testTakerAnswers);
cout << "\nGrade another exam (Y/N)? ";
cin >> doAnother;
while (doAnother != 'Y' && doAnother != 'N' && doAnother != 'y' && doAnother != 'n'){
cout << doAnother << " is not a valid option. Try Again y/Y or n/N" << endl;
cin >> doAnother;}
cout << endl;
cin.ignore();
}while(doAnother != 'N' && doAnother != 'n');
return 0;
}
Your issue is cin >> testTakerAnswers[i]; cin is whitespace delimited, that means that any whitespace (including '\n') will be discarded. So testTakerAnswers[i] can never be '\n'.
I'm not sure exactly what you want to do, but possibly try
getline(cin,input_string);
then
input_string == "A" | input_string == "B" | ...
So if only the enter key is pressed, input_string will become "".
Pretty new here to programming, and I have an assignment where I need to achieve the following:
ask for total amount of people
get each of their names
allow user to enter up to 5 scores for each person
if there are less than 5 scores for a given person, inputting -100 will stop it
So far I have written this:
#include <iostream>
using namespace std;
int main() {
string personName;
int totalPerson, personScoreCounter;
double personGrade, personGradeTotal;
cout << "Input total amount of people: ";
cin >> totalPerson;
for (int person = 1; person <= totalPerson; person++)
{
cout << "Input name for person " << person << ": ";
getline(cin, personName);
cin.ignore();
while ( (personGrade != -100) && (personScoreCounter <= 5) )
{
cout << "Input up to 5 scores for " << personName << " (-100 to end): ";
cin >> personGrade;
if (personGrade >= 0 && personGrade <= 100) // valid range of scores
{
personGradeTotal += personGrade;
personScoreCounter++;
}
else
{
cout << "Input only scores from 0-100" << endl;
}
cout << "Input up to 5 scores for " << personName << " (-100 to end): ";
cin >> personGrade;
}
}
// calculate averages and other stuff in here.
return 0;
}
After getting their name, only the last cout inside the while loop seems to execute first, then it starts from the top and so on until the for loop hits the end depending on totalPerson. I know I'm missing a few things in here, probably in the order of operations and also the way I am executing my loops, but I just can't see it. Could any of you guys with experience in the language please give me any pointers as to what's happening here and how I can fix it? Thank you.
Inside your while group, you only want to use your cout line once (at the beginning looks good).
Your first check should be for ==-100 or similar, since as it is now, you'll get a "Input only scores from 0 to 100" message if you enter -100.
You should keep a cin.ignore(); call after each use of cin >> VARIABLE, since then you will drop the EoL character.
Example code:
#include <iostream>
using namespace std;
int main() {
int totalPerson;
cout << "Input total number of people: ";
cin >> totalPerson;
cin.ignore();
for (int person = 1; person <= totalPerson; person++)
{
int personScoreCounter=0;
double personGrade = -1, personGradeTotal=0;
string personName;
cout << "Input name for person " << person << ": ";
std::getline(cin, personName);
while ( (personGrade != -100) && (personScoreCounter < 5) )
{
cout << "Input up to 5 scores for " << personName << " (-100 to end): ";
cin >> personGrade;
cin.ignore();
if (personGrade == -100) {
break;
} else if (personGrade >= 0 && personGrade <= 100) {
personGradeTotal += personGrade;
personScoreCounter++;
} else {
cout << "Input only scores from 0-100" << endl;
}
}
// calculate averages and other stuff in here.
double avg = personGradeTotal / personScoreCounter;
cout << "Avg = " << avg << endl;
}
return 0;
}
Some of your variables also needed to move inside the for loop.
Additionally I changed the limits on the personScoreCounter to [0:4] rather than [1:5] - this way you can use it for averaging more easily.
You might also try cin.getline() instead of getline(std::cin , ... ):
int max_length = 30;
std::cin.getline(personName, max_length, '\n'); // \n is option termination.
This allows whitespaces in the input also.
http://www.cplusplus.com/reference/istream/istream/getline/
Using C++ (g++-4.7 on Mint 16).
Code is a unrefined (and unfinished) Tic-Tac-Toe game.
#include <iostream>
using namespace std;
int main()
{
//initial data
char turn='A';
char ttt[] = {'1','2','3','4','5','6','7','8','9'};
int move;
int over=0; //0 is no, 1 is yes
int valid=0;
while ( over == 0)
{
//display
cout << "\n" << ttt[0] << "|" << ttt[1] << "|" << ttt[2] <<"\n-----\n";
cout << ttt[3] << "|" << ttt[4] << "|" << ttt[5] <<"\n-----\n";
cout << ttt[6] << "|" << ttt[7] << "|" << ttt[8] <<"\n\n Choose a number (Player " << turn << "):";
//ask enter for play with turn
cin >> move;
cout << "\n";
valid = 0;
while (valid == 0)
{
//check if input is valid
if (((move > 0) and (move < 10)) and
((ttt[move-1] != 'A') and (ttt[move-1] != 'B')) and
(cin))
{
ttt[move-1] = turn;
valid=1;
}
else
{
cout << "Invalid slot. Choose a number (Player " << turn << "):";
cin >> move;
cout << "\n";
}
}
//check if done if no //change turn then goto //display
if (((ttt[0]==ttt[1]) and (ttt[1]==ttt[2])) or
((ttt[3]==ttt[4]) and (ttt[4]==ttt[5])) or
((ttt[6]==ttt[7]) and (ttt[7]==ttt[8])) or
((ttt[0]==ttt[3]) and (ttt[3]==ttt[6])) or
((ttt[1]==ttt[4]) and (ttt[4]==ttt[7])) or
((ttt[2]==ttt[5]) and (ttt[5]==ttt[8])) or
((ttt[0]==ttt[4]) and (ttt[4]==ttt[8]))or
((ttt[2]==ttt[4]) and (ttt[4]==ttt[6])))
{
//display winner or say draw
cout << "Player " << turn << " wins!\n";
over=1;
}
else
{
//change turn
if (turn=='A')
{ turn='B';
}
else
{ turn='A';
}
}
}
return 0;
}
There seem to be a bug on the code. On the part where check if input is valid the and (cin) seem to be failing.
When entering a character, (Instead of a number) it output continuously stacks of:
Invalid slot. Choose a number (Player A or B):
I tested the rest of condition without it, it was all working well. Is there a problem on the code or is this really "cin" problem? I've also tried out !(!cin) but it's the same scenario.
You must clear the fail bit from the cin stream in your else block.
When you enter a character that isn't an integer, the cin stream sets the fail bit, which you correctly check for in your if statement, but you never clear it afterward. This causes your input validity check to be false forever.
#include <limits>
...
else
{
cin.clear(); // Add this line
cin.ignore(numeric_limits<streamsize>::max(), '\n'); // And this one
cout << "Invalid slot. Choose a number (Player " << turn << "):";
cin >> move;
cout << "\n";
}
For additional information, see the documentation for std::basic_ios::clear
Update: see this question and this question for similar problems.
Essentially, you also need to tell cin to ignore whatever is in the stream or it will continually set the fail bit with its bad contents you haven't cleared yet. I modified the above snippet to work.
I wrote a program for my computer science class that validates and solves sudoku puzzles from .txt files, but I wanted to take it one step further and write a program that made it easy to input and sudoku game. I'm sure you can figure out the format of the files based on this code. My only problem is that the last cin gets skipped, and that option is important to me. Any insight will be appreciated!!
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
struct s {
s();
~s() {/*zzzz*/}
void show_grid();
void set (int &r, int &c, int &v) {g[r][c] = v;}
private:
int g[9][9];
};
//************************************************************************
void s::show_grid() {
//print game out to check it
cout << " | ------------------------------- |" << endl;
for (int k=0; k<81; k++) {
if (k%3 == 0)
cout << " |";
cout << " " << g[k/9][k%9];
if (k%9 == 8) {
cout << " |" << endl;
if ((k/9)%3 == 2)
cout << " | ------------------------------- |" << endl;
}
}
cout << endl;
}
//************************************************************************
s::s() {
//initialize all elements to zero
for (int i=0; i<9; i++) {
for (int j=0; j<9; j++) {
g[i][j] = 0;
}
}
}
//************************************************************************
void create_name (string &name) {
//append .txt extension LIKE IT OR NOT
string ext = name;
ext.erase(ext.begin(), ext.end() - 4);
if (ext.compare(".txt")!=0)
name.append(".txt");
}
//************************************************************************
int main () {
s g;
string name;
string yon("");
int count = 0;
int row, col, val, rcv;
ofstream os;
cout << "Enter game file name: ";
cin >> name;
create_name(name);
//open and do typical checks
os.open(name.c_str());
if (os.fail()) {
cerr << "Could not create " << name << ". Waaaah waaaaaaaaaah...\n\n";
return 0;
}
//useful output (hopefully)
cout << "Enter grid coordinates and value as a 3-digit number,\n"
<< "from left to right, row by row.\n"
<< "(e.g. 2 in first box would be 112)\n";
//take input as one int, to be user friendly
while (cin >> rcv && count < 81) {
row = (rcv / 100) - 1;
col = ((rcv / 10) % 10) - 1;
val = rcv % 10;
os << row << " " << col << " " << val << endl;
g.set (row, col, val);
count++;
}
os.close();
//From here down is broken, but it still compiles, runs, and works
cout << "Show grid input(y/n)?\n";
cin >> yon;
if (yon.compare("y")==0)
g.show_grid();
else if (yon.compare("n")==0)
cout << "Peace!\n";
return 0;
}
The problem is here:
while (cin >> rcv && count < 81)
Consider what happens when count==81: First, rcv will be input from cin, and only then the condition count < 81 will be evaluated to false. The loop will stop, and the value of rcv will be ignored. So effectively you read one input too many.
You should change the order of evaluation, so that count is checked first:
while (count < 81 && cin >> rcv)
Edit:
According to your comment above you are actually expecting to read less than 81 values. In that case, I recommend having the user input a special value (for example, 0) to terminate the loop. You'd just need to add if (rcv==0) break;. If you just input an invalid value as you are apparently doing, the cin stream will be put in a failed state and further input will not succeed.
Try something like:
//useful output (hopefully)
cout << "Enter grid coordinates and value as a 3-digit number,\n"
<< "from left to right, row by row.\n"
<< "(e.g. 2 in first box would be 112)\n"
<< "or Z to end the loop\n"; // 1
//take input as one int, to be user friendly
while (count < 81 && cin >> rcv ) { // 2
row = (rcv / 100) - 1;
col = ((rcv / 10) % 10) - 1;
val = rcv % 10;
os << row << " " << col << " " << val << endl;
g.set (row, col, val);
count++;
}
if(!std::cin) { // 3
std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
1) Let the user know that he can enter in invalid char. It doesn't have to be Z, actually any non-numeric char will work.
2) Fix off-by-one error in the order of the &&.
3) If std::cin is in error state, clear the error and ignore the Z.
cin >> yon
still actually reads in a variable, it just reads in the variable that the while loop found to be false. When the while loop condition returns false rcv is ignored, so the number remains in the input stream waiting for the next cin statement. When yon is called that number meant for rcv is read into yon, giving you some strange errors.
it would be better to use interjay's method:
while (count < 81 && cin >> rcv)