I have tried to list prime numbers using C++ Do-While loop but I have trouble and not found problems inside my code. Can any one help me in this?
I have tried so far:
#include <iostream>
using namespace std;
int main()
{
int num2check = 3, innerCheck;
bool isPrime;
do
{
isPrime = true;
innerCheck = 2;
while ((innerCheck < num2check) && (isPrime == true));
{
if (num2check % innerCheck == 0)
{
isPrime = false;
break;
}
else
{
innerCheck++;
}
}
if (isPrime == true)
{
cout << num2check << " is prime.";
num2check++;
}
else
{
num2check++;
}
}while(num2check < 50);
return 0;
}
You need to remove the semicolon in this line
while ((innerCheck < num2check) && (isPrime == true));
In programming standards, the ; signifies an end of statement, or in this case that it is a null statement, so here the while loop doesn't executes anything and keeps on running in infinite loop as the condition will always holds true
Related
I was wondering what I may have done wrong in writing this simple function which is supposed to return true if the given number is a prime, or false if not a prime.
bool isPrime(int num)
{
if (num <= 1)
{
status = false;
}
else
{
for (int i = 1; i <= num; i++)
{
if (num % i == 0)
{
dividers++;
}
}
if (dividers == 2)
{
status = true;
}
else
{
status = false;
}
}
return status;
}
Obviously, my main looks like this:
bool isPrime(int num);
bool status;
int dividers = 0;
int main() {
isPrime(2);
if (!isPrime)
{
std::cout << "Not prime" << std::endl;
}
else
{
std::cout << "Prime" << std::endl;
}
return 0;
}
I'm a C++ beginner and I'd really appreciate it if someone could help me there and correct my logic.
Have a good day:)
The immediate problem is in this two lines:
isPrime(2);
if (!isPrime)
The first line calls the function and discards the returned value. The second line converts a pointer to the function to bool. The output of your code does not depend on what you actually do in isPrime.
That is not how you call a function and use its result!
Instead you want
if (isPrime(2)) {
or
bool isP = isPrime(2);
if (isP) { ...
As mentioned in comments, there are also problems in the implementation of isPrime, but I hope this is enough to set you back on the right track.
PS: You should get rid of the global variable status. You do not need both, the return value and a global that stores the result, and if you can choose, you should definitely go for the return value.
I have written the following infix to postfix program but it's not working.
My program takes input but doesn't show any result. Can anyone help find the problem in my program.
And also it would be a great help if you tell if my Algorithm for converting infix to postfix is correct or not.
using namespace std;
class Stack
{
private:
int top;
char s[mx];
public:
Stack()
{
top=-1;
}
void push(char c)
{
if(!stackFull())
s[++top]=c;
}
void pop()
{
if(!stackEmpty())
top--;
else cout<<"Stack is empty"<<endl;
}
char topShow()
{
if(!stackEmpty())
return s[top];
}
bool stackEmpty()
{
if(top==-1)
return 1;
else return 0;
}
bool stackFull()
{
if(top == (mx-1))
return 1;
else return 0;
}
};
class Expression
{
private:
char entry2;
int precedence;
char infix[mx];
char postfix[mx];
public:
int prec(char symbol)
{
switch(symbol)
{
case '(':return 0; break;
case '-':return 1; break;
case '+':return 2; break;
case '*':return 3; break;
case '/':return 4; break;
}
}
void Read()
{
cout<<"Enter the infix expression: ";cin>>infix;
for(int i=0;infix[i]!='\0';i++)
{
convertToPostfix(infix[i]);
}
}
void ShowResult()
{
cout<<"Postfix expression"<<endl;
for(int j=0;postfix[j]!='\0';j++)
{
cout<<postfix[j];
}
}
void convertToPostfix(char c)
{
int p=0;
Stack myStack;
precedence=prec(c);
entry2=myStack.topShow();
if(isdigit(c))
{
postfix[++p]=c;
}
if(precedence>prec(entry2))
{
myStack.push(c);
}
if(precedence<prec(entry2))
{
switch(c)
{
case '(': myStack.push(c); break;
case ')': while(myStack.topShow()!= '(')
{
postfix[++p]=myStack.topShow();
myStack.pop();
};myStack.pop();break;
case '+':
case '-':
case '*':
case '/': while(prec(myStack.topShow())>=precedence)
{
postfix[++p]=myStack.topShow();
myStack.pop();
};break;
}
}
}
};
int main()
{
Expression myExp;
myExp.Read();
myExp.ShowResult();
return 0;
}
Here are some issues I found:
Boolean Functions Return true or false
Match return types with return values. The numbers 1 and 0 are not Boolean values.
Precedence table
Add and subtract have same precedence.
Multiply and divide have same precedence.
Multiply and divide have higher precedence than add and subtract.
Stack disappears
Since the stack is declared as a local variable in the function, it will be created fresh when entering the function and destroyed before exiting the function.
Solution: move it to the class as a class member or declare it as static.
Multiple statements per line are not more efficient
Blank lines and newlines do not affect performance, and add negligible time to the build.
However, they make your program more readable which helps when inspecting or debugging. Use them.
And similarly with space before and after operators.
Build the habit now rather than correcting when you get a job.
Call function once and store the value
You call prec(entry2) twice, which is a waste of time. Call it once and save the value in a variable. Similarly with stack.TopShow().
Use std::vector not an array
The std::vector will grow as necessary and reduce the chance of buffer overflow.
With an array, you must check that your indices are always within range. Also, array capacities don't change; you have to declare a new instance and copy the data over.
The variable mx is not declared
The compiler should catch this one. You use mx as the capacity for an array and comparing for full. However, it is never declared, defined nor initialized. Prefer std::vector and you won't have to deal with these issues.
Input is not validated
You input a letter, but don't validate it.
Try these characters: space, #, #, A, B, etc.
Missing default for switch
Crank up your compiler warnings to maximum.
Your switch statements need defaults.
What precedence do numeric characters ('0'..'9') have?
(You check the precedence of numeric characters.)
Check all paths through your functions and program.
Using a debugger (see below) or pen and paper, check your program flow through you functions. Include boundary values and values not within the bounds.
Case statements: break or return
You don't need a break after a return statement. Think about it. Can the program continue executing at the line after a return statement?
Use a debugger or print statements
You can print variables at different points in your program. This is an ancient technique when debuggers are not available.
Learn to use a debugger. Most IDEs come with them. You can single step each statement and print out variable values. Very, very, useful.
class infixToPostfix{
public static void postfix(String str){
Stack<Character> stk = new Stack<Character>();
for(Character c : str.toCharArray()){
// If operands appears just print it
if(c >= 'A' && c <= 'Z' || c >= 'a' && c <= 'z'){
System.out.print(c);
}else{
// Open paranthesis push is
if(c == '('){
stk.push(c);
//Close paranthesis pop until close paranthesis
}else if( c == ')'){
while(stk.peek() != '(')
System.out.print(stk.pop());
stk.pop();
// check the precedence of operator with the top of stack
}else if(c == '+' || c == '-'){
if(!stk.isEmpty()){
char top = stk.peek();
if(top == '*' || top == '/' || top == '+' || top == '-'){
System.out.print(stk.pop());
}
}
stk.push(c);
}else{
if(!stk.isEmpty()){
char top = stk.peek();
if(top == '/' || top == '*'){
System.out.print(stk.pop());
}
}
stk.push(c);
}
}
}
//Print all the remaining operands
while(!stk.isEmpty()) System.out.print(stk.pop());
System.out.println();
}
public static void main(String args[]){
String str = "A+B-(c+d*Z+t)/e";
postfix(str);
}
}
using stack and map u can solve the problem
1) create a map having operator as key and some integer to set priority. operator with same precedence will have same value something like:
map<char,int>oprMap;
oprMap['^'] = 3;
oprMap['*'] = 2;
oprMap['/'] = 2;
oprMap['+'] = 1;
oprMap['-'] = 1;
2) iterate through given expression call these checks
1) if current element
i) is operand add it to result
ii) not operand do following check
a. while not (stack is empty and element is open bracket and found operator with higher precedence.
add top of the stack to the result and pop()
b. push current element to stack
iii) if open brackets push to stack
iv) if closed brackets pop until get closed bracket and add it to result
3) while stack is not empty pop() and add top element to the result.
{
stack<char>S;
for (int i = 0; i < n; i++) {
if(isOperand(exps[i])) {
res = res + exps[i];
} else if(isOperator(exps[i])){
while(!(S.empty() && isOpenParanthesis(S.top()) && isHeigherPrecedence(S.top(),exps[i])){
res = res+S.top();
S.pop();
}
S.push(exps[i]);
} else if(isOpenParanthesis(exps[i])) {
S.push(exps[i]);
} else if(isClosingParanthesis(exps[i])) {
while(!S.empty() && !isOpenParanthesis(S.top())) {
res = res+S.top();
S.pop();
}
S.pop();
}
}
while(!S.empty()) {
res = res + S.top();
S.pop();
}
}
}
#include<bits/stdc++.h>
using namespace std;
// This isHigher function checks the priority of character a over b.
bool isHigher(char a,char b)
{
if(a=='+' || a=='-')
return false;
else if((a=='*' && b=='*') || (a=='*' && b=='/') || (a=='/' && b=='*') ||
(a=='/' && b == '/')|| (a=='^' && b=='^')||(a=='*' && b=='^') || (a=='/' &&
b=='^'))
return false;
return true;
}
int main(){
string s;
cin>>s;
s = s + ")";
//Vector postfix contains the postfix expression.
vector<char>postfix;
stack<char>mid;
mid.push('(');
for(int i=0;i<s.length();i++)
{
if(s[i] == '(')
mid.push(s[i]);
else if(s[i] == '+' || s[i] == '^' || s[i] == '-' || s[i] == '*'||
s[i] == '/')
{
if(mid.top() == '(')
mid.push(s[i]);
else {
if(isHigher(s[i],mid.top()))
mid.push(s[i]);
else
{
while(mid.top()!='(')
{
if(!isHigher(s[i],mid.top()))
{
postfix.push_back(mid.top());
mid.pop();
}
else
break;
}
mid.push(s[i]);
}
}
}
else if(s[i] == ')')
{
while(mid.top() != '(')
{
postfix.push_back(mid.top());
mid.pop();
}
mid.pop();
}
else
postfix.push_back(s[i]);
}
for(int i=0;i<postfix.size();i++)
cout<<postfix[i];
return 0;
}
Suppose I have a while loop that depends on two separate inputs. In situation one, the while loop will take the value 1, and in situation two, it should take !cin.eof(). Is there a way I can do this efficiently? To be more concise:
string hello;
cin >> hello;
if(hello == "one")
{
//make the while loop depend on value 1
}
else if(hello == "two")
{
//make the while loop depend on value !cin.eof()
}
while(/*depends on above conditional*/)
{}
I don't want to do something like:
if(hello == "one)
{
while(1){}
}
else if(hello == "two")
{
while(!cin.eof){}
}
because the while loop essentially does the same thing in each situation.
For readability and in the interest of cohesion, I think you should move the contents of your loop into a separate function:
void DoSomething() { /* ... */ }
// ...
if(hello == "one)
{
while(1){ DoSomething(); }
}
else if(hello == "two")
{
while(!cin.eof){ DoSomething(); }
}
It's easier to see that the different while loops are doing the same thing but their conditions are different.
I believe you're looking for something like this:
while((hello == "one") || (hello == "two" && !cin.eof)) {
}
This code will do what you want, because it checks 'is the variable "one"? If so, keep executing. If it's not, it'll check: Is the variable "two"? If so, it'll check for cin.eof.
If it's neither, the loop won't execute. (the && 1 in the first condition was omitted, because it's always 'true', equalling and infinite loop)
Edit:
To simplify things, you may want to consider this code (as suggested in the comments):
bool HelloIsOne = (strcmp(hello, "one") == 0);
bool HelloIsTwo = (strcmp(hello, "two") == 0);
while(HelloIsOne || HelloIsTwo && !cin.eof) {
}
The brackets, which I placed in the previous example are actually unnecessary, because && binds stronger than ||, but they help the general clarity of the code.
Simply use or (||) as a condition in the while loop. Set the first condition if(hello == "one"). Now you have a while loop that will loop if one of the conditions is true.
bool value = hello == "one";
while (value || !cin.eof) {}
If you're using C++11:
#include <functional>
auto check = (hello == "one") ? []() bool -> { return 1; } :
[]() bool -> { return !cin.eof(); };
while(check) {
};
How about this:
switch(hello)
{
case 'one':
{
for(; 1; );
{
// your loop here
}
break;
}
case 'two':
{
for(;!cin.eof; )
{
// your other loop here
}
break;
}
default:
{
cout << " shouldnt get here unless bad user input" << endl;
break;
}
}
You can do something like this:
#include <iostream>
#include <string>
using namespace std;
int main()
{
string hello;
cin >> hello;
while(hello=="one"?1:(!cin.eof()))
{
//do stuff
}
return 0;
}
It checks if the string hello is "one" and if it's true, the condition of the while is 1, else it is !cin.eof() as you wanted.
I am trying to break out of several nested while loops and I am having trouble. I want this program to break out into the outer loop, which will run only a certain amount of times. I tried doing it with a boolean but my program terminates too early. It is an N-Queens problem where I am solving for 1x1, 2x2, 3x3,...nxn queens.
Here is my code:
bool ok(int *q, int col)
{
for(int i=0; i<col; i++)
if(q[col]==q[i] || (col-i)==abs(q[col]-q[i])) return false;
return true;
};
void print(int q[], int n, int cnt)
{
//static int count =0;
cout<<"There are "<<cnt<<" solutions for "<<n<<" queens." <<endl;
};
int main()
{
int n;
int *q;
cout<<"Please enter the size of the board:"<<endl;
cin>>n;
int static count = 0;
int c = 1;
int a = 1;
bool from_backtrack=false;
while(a!=n){
q= new int[a];
q[0]=0;
bool foundSolution=true;
while(foundSolution)
{
if (c==a){
a++;
}
while(c<a)
{
if(!from_backtrack)
q[c] = -1; //Start at the top
from_backtrack=false;
while(q[c]<a)
{
q[c]++;
if (q[c]==a)
{
c--;
if(c==-1) {
print(q, n, count);
foundSolution=false;
//system("PAUSE"); exit(1);
}
continue;
}
if( ok(q,c) ) break; //get out of the closest while loop
}
c++;
}
count++;
c--;
if(c==-1) {
print(q, n, count);
foundSolution=false;
//system("PAUSE"); exit(1);
}
from_backtrack=true;
}
delete[a] q;
a++;
}
system("PAUSE");
}
The most elegant way would be to wrap some of your inner loops in a function.
It will be easier to read and to control.
At my work, we employ MISRA guidelines which state "... only 1 break per while loop". This has caused me to rewrite my if and while loops:
bool can_continue = true;
if (can_continue)
{
status = Do_Something();
if (status != SUCCESS)
{
can_continue = false;
}
}
if (can_continue)
{
status = Do_Another_Thing();
can_continue = status == SUCCESS;
}
//.. and so on.
The idea is to set a flag to "false" if execution can't continue. Check it after any segment can cause execution to fail.
while( true ){
if( condition == true ){
goto bye;
}
}
:bye
Just don't submit this on your homework...
Think it is as crazy as useless.
However, suppose you want 3 iterations, you'll define an array of bool of 3 elements (all set to true). On each iteration you set the current element to false, until you reach the end of your array.
I have had a similar issue with quite a few projects I have worked on involving classes containing arrays. I have a class that is supposed to handle a 2 dimensional matrix representing a TicTacToe game. There is an enumeration in the class for the status of the current game and one member function that has an enumeration return type. I cant seem to figure out why I can create the class set values in the matrix and as soon as I call the member function with the enumerated return type the whole array is reinitialized to 0. I think it has something to do with the constructor being called again or something along those lines but I have not been able to find anything after searching for the past few hours. Any help would be greatly appreciated.
Here is my header file containing the class information:
#ifndef TTT_H
#define TTT_H
#include <cstdlib>
#include <iostream>
using namespace std;
class TicTacToe
{
private:
enum Status{WinX, WinO, Continue, Draw};
int **board;
public:
TicTacToe();
~TicTacToe();
void PrintBoard();
bool ValidMove(int, int);
bool PlayerMove(int, int, int);
Status GameStatus(); //this one causes the problem
void Debug();
};
#endif
Here is the code for CPP file with the member function definitions:
#include "TicTacToe.h"
#include <iostream>
#include <cstdlib>
#include <iomanip>
#include <cassert>
using namespace std;
TicTacToe::TicTacToe()
{
board = new int*[3];
assert(board != 0);
for(int i=0;i<3;i++)
{
cout << "Constructor Ran again" << endl; //for testing
board[i] = new int[3];
assert(board[i] != 0);
for(int j=0;j<3;j++)
board[i][j] = 9;
}
}
TicTacToe::TicTacToe(TicTacToe ©)
{
board = new int*[3];
assert(board != 0);
}
TicTacToe::~TicTacToe()
{
if(board)
delete[] board;
}
void TicTacToe::PrintBoard()
{
for(int i=0;i<3;++i)
{
for(int j=0;j<3;++j)
{
cout << "| ";
switch(board[i][j]){
case 0:
cout << "O ";
break;
case 1:
cout << "X ";
break;
case 9:
cout << " ";
break;
}
}
cout << "|" << endl;
cout << "------------" << endl;
}
}
bool TicTacToe::ValidMove(int row, int col)
{
bool valid = false;
if(row < 3 && col < 3)
{
if(board[row][col] == 9)
valid = true;
}
return valid;
}
bool TicTacToe::PlayerMove(int player, int row, int col)
{
bool done = false;
if(ValidMove(row,col) == true)
{
if(player == 1)
board[row][col] = 1;
else
board[row][col] = 0;
done = true;
}
return done;
}
TicTacToe::Status TicTacToe::GameStatus() //This function is the problem
{
int check, empty = 0;
bool done = false;
for(int i=0;i<3;++i)
{
for(int j=0;j<3;++j)
{
check += board[i][j];
if(board[i][j] = 9)
empty++;
}
if(check == 0)
return WinO;
else if(check == 3)
return WinX;
check = 0;
}
if(empty == 0)
return Draw;
for(int i=0;i<3;++i)
{
for(int j=0;j<3;++j)
check += board[j][i];
if(check == 0)
return WinO;
else if(check == 3)
return WinX;
check = 0;
}
check = board[0][0] + board[1][1] + board[2][2];
if(check == 0)
return WinO;
else if(check == 3)
return WinX;
check = 0;
check = board[0][2] + board[1][1] + board[2][0];
if(check == 0)
return WinO;
else if(check == 3)
return WinX;
check = 0;
return Continue;
}
void TicTacToe::Debug()
{
//cout << &board[0][0] << endl;
for(int i=0;i<3;++i)
{
for(int j=0;j<3;++j)
cout << board[i][j];
cout << endl;
}
}
Here is the driver file I am using to test:
#include "TicTacToe.h"
#include <iostream>
#include <cassert>
using namespace std;
int main()
{
int row, col;
bool valid;
enum Status{WinX, WinO, Continue, Draw};
TicTacToe * T;
T = new TicTacToe;
assert(T != 0);
cout << "There are 2 players. P1 is x P2 is o" << endl;
do
{
T->PrintBoard();
valid = false;
while(valid == false)
{
cout << "\nP1 choose a cell" ;
cin >> row >> col;
if(T->ValidMove(row, col) == true)
{
T->PlayerMove(1, row, col);
valid = true;
}
else
{
cout << "Not a valid choice" << endl;
valid = false;
}
}
T->PrintBoard();
cout << endl;
T->GameStatus(); //<<<<<this is the pain in my butt
T->PrintBoard();
valid = false;
while(valid == false)
{
cout << "\nP2 choose a cell" ;
cin >> row >> col;
if(T->ValidMove(row, col) == true)
{
T->PlayerMove(2, row, col);
valid = true;
}
else
{
cout << "Not a valid choice" << endl;
valid = false;
}
}
}
while(/*T->GameStatus() == Continue*/ 1==1);
//the call to GameStatus was commented out of the
//while statement for testing
return 0;
}
I know the code inside of the GameStatus function is far from pretty but the array is messed up before any of those lines are processed.
I left all of the other functions just to show that they work properly without issue.
Thanks in advance for any help you may be able to give.
You've got a simple typo in your code..
if(board[i][j] = 9) // will always return true (refp)
empty++;
Other remarks
When looking at your code a bit more thoroughly I see that you have a few other miss-happens, intentional or unintentional.. that I don't know:
int check is not initialized in TicTacToe::GameStatus
You are not freeing the allocated memory properly, you'll
need to free all entries in board, ie. delete board[i])
I don't like bugs, how can I get rid of the operator= vs operator== problem?
A quite common method to circumvent the problem of making a typo and writing = when you mean to compare (==) two variables is to flip the operands around (if one of them is a constant value, such as 9.
if(9 = board[i][j]) will not compile and such a bug would've never appeared in your code.
I'll have to say that I don't like writing my statements that way.. though it's a quite common method, especially in the "beginner" segment.
check is not initialized in GameStatus() .
if (board[i][j] = 9)
Isn't the above line of code resetting the array contents? You probably want to use == here, instead.
You have a serious issue in memory management. Look:
Your constructor performs 4 allocations (an array of pointers and 3 arrays of ints, to emulate a 2D arrray),
Your destructor performs 1 deallocation (= memory leak),
You have a custom destructor but you don't define (or block) operator= (you need to, see What is The Rule of Three?)
Your copy constructor is incomplete and doesn't create a "valid" object.
Basically the above is likely to cause you some memory problems. I suggest to:
Rewrite the destructor to first free all the arrays of ints, then the array of pointers,
Make the class TicTacToe uncopiable by declaring the copy constructor and the operator= as private.
Also some minor details on that matter:
board = new int*[3];
assert(board != 0);
The assertion is unnecessary. If the allocation fails, the operator new will throw an exception.
if(board)
delete[] board;
Operators delete and delete[] don't do anything if their argument is a null pointer, so that condition is redundant. Also you have designed your object with the invariant that the board exists as long as the TicTacToe object exists, so that check is totally unnecessary, right?
Keep it safe and simple!