c++ newb inquiry

[de_mystiX]

I've been searching these forums and trying to figure this out on my own but am having problems.

int x;
cin >> x;

if a noninteger value is entered the program goes into an endless loop - is there anything that can be done about this? :confused:

thanks - if you can help elucidate this i would appreciate it as i'm trying to get a firm grasp on c++ and this is throwin off my game

[de_mystiX]

so it looks like it loops because of a condition i had set - but if it is passed a noninteger value it just ignores every condition and falls through the code till it returns

any suggestions?

[Banfa]

Not unless you post the code that is causing the problem

[de_mystiX]

#include <cstdlib>
#include <iostream>
#include <string>
#include <vector>

/*This program takes two int, one coefficient, and one exponent to calculate the
power of the coefficient - it stores each multiplication in a vector and displays
the progression from 1 through...*/

using namespace std;

//function declaration

int powervec(int coef, int expo, vector<int> &chamber);

int main(int argc, char *argv[])
{
int x = 0, y = 0;

char s; //input character for y/n response
int cnt = 1; //counter for exponential count
int check = 1;//control variable to control loop through process

while(check == 1)//repeat loop while response 'y'
do
{

cnt = 1; //reset counter to 1

cout << "\nEnter two values - One Coefficient & One Exponent\n\n\n";
cout << "Enter Coefficient: ";

while(!(cin >> x))
{cout << "\n!!!invalid input received!!!\n\nTry again...\n\n"; break;}
cout << "\nEnter Exponent: ";
while(!(cin >> y))
{cout << "\n!!!invalid input received!!!\n\nTry again...\n\n"; break;}
cout << endl;
if(y == 1 && x == 1)
{cout << "\n1 multiplied by 1 is 1\n\n";
cout << "do you want to try again?(y or n):"; cin >> s;
if(s == 'y'){break;}
else {check = 0; break;}
}
vector<int> powvector(y);

powervec(x,y,powvector);

for(vector<int>::iterator iter = powvector.begin(); iter != powvector.end(); iter++, cnt++)
{
cout << x << " to the power of " << cnt << " is: " << *iter << endl;
}

cout << "\nCalculate another power??? (y or n):";

cin >> s;

if(s == 'n'){check = 0;} //escape loop

}while (s == 'y' || s == 'Y');

cout << "\nThank you for calculating powers with my program!!!\n" << endl;

system("PAUSE");
return EXIT_SUCCESS;

}

int powervec(int coef, int expo, vector<int> &chamber)
{
int total = 1;

for(int num = 0; num != expo; num++)
{
total *= coef;
chamber[num] = total;
}

return total;

}

------------------------------------------------------------------------

Again, when ever you enter a noninteger value into x or y, the program loops endlessly.

[Banfa]

My Comments embedded in the code in bold

// MethodTest.cpp : Defines the entry point for the console application.
//
 
#include <cstdlib>
#include <iostream>
#include <string>
#include <vector>
 
/*This program takes two int, one coefficient, and one exponent to calculate the
power of the coefficient - it stores each multiplication in a vector and displays
the progression from 1 through...*/
 
using namespace std;
 
//function declaration
 
int powervec(int coef, int expo, vector<int> &chamber);
 /* Since this is in the same module as the place it is 
   called from you could prefix this with static */
 
int main(int argc, char *argv[])
{
    int x = 0, y = 0;
 
    char s; //input character for y/n response
    int cnt = 1; //counter for exponential count
    int check = 1;//control variable to control loop through process
 /* You seem to be using check as a boolean control variable so why 
   not use the typer bool?  Also check is not very descriptive of what 
   this variable does a name like bContinueRunning might be better */
 
    while(check == 1)//repeat loop while response 'y'
 /* This loop is a bit unnecessary, you could just add the 
   condition to the conditions of the do loop like so
 
        }while ((s == 'y' || s == 'Y') && check == 1); 
 
   Although you would also need to change some of your 
   breaks to continues. */
 
        do
        {
 
            cnt = 1; //reset counter to 1
 
            cout << "\nEnter two values - One Coefficient & One Exponent\n\n\n";
            cout << "Enter Coefficient: ";
 
            while(!(cin >> x))
            {cout << "\n!!!invalid input received!!!\n\nTry again...\n\n"; break;}
 /* This line is part of your problem, you detect the error and output a
   message (cout statement) but instead of re-requesting input you 
   then break out of the loop this code is equivilent to 
 
    if(!(cin >> x))
    {
        cout << "\n!!!invalid input received!!!\n\nTry again...\n\n"; 
    }
 
    this means that if the input value is invalid the program just goes ahead and tries to use it.
*/
 
 /* Your source format is very poor and makes the code less readable, 
   which in turn makes it harder to maintain the 2 normal ways of laying
   out the braces of a loop or if statement would be 
 
    while(!(cin >> x)) {
        cout << "\n!!!invalid input received!!!\n\nTry again...\n\n"; 
        break;
    }
 
   or
 
    while(!(cin >> x))
    {
        cout << "\n!!!invalid input received!!!\n\nTry again...\n\n"; 
        break;
    }
 
   personally I prefer the second.  Formated like this you might have 
   spotted the break error.
*/
            cout << "\nEnter Exponent: ";
            while(!(cin >> y))
            {cout << "\n!!!invalid input received!!!\n\nTry again...\n\n"; break;}
 /* Again the same break problem and source code formating.*/
            cout << endl;
            if(y == 1 && x == 1)
            {cout << "\n1 multiplied by 1 is 1\n\n";
 /* Source code formating. */
            cout << "do you want to try again?(y or n):"; cin >> s;
            if(s == 'y'){break;}
 /* Source code formating and here you only check for y but later 
   on you check for y and Y, you should keep these checks consistent.
   Additionally you are actually repeating the code to ask if the user 
   wants to perform another calculation.  This is bad form as it introduces 
   a maintence issue (if you want to change the method you have to 
   change it in 2 places).  By reorganising the if with an else clause 
   you can have the code that checks for a repeat calculation once at 
   the end of the loop removing this issue. This would also allow you to 
   remove the outer while loop entirely and the variable check. */
            else {check = 0; break;}
 /* Source code formating. */
            }
            vector<int> powvector(y);
 
            powervec(x,y,powvector);
 
            for(vector<int>::iterator iter = powvector.begin(); iter != powvector.end(); iter++, cnt++)
            {
                cout << x << " to the power of " << cnt << " is: " << *iter << endl;
            }
 
            cout << "\nCalculate another power??? (y or n):";
 
            cin >> s;
 
            if(s == 'n'){check = 0;} //escape loop
 /* Source code formating and below you check for y and Y, but here 
   you ar checking for n you should keep your checks */
 
        }while (s == 'y' || s == 'Y');
 
        cout << "\nThank you for calculating powers with my program!!!\n" << endl;
 
        system("PAUSE");
        return EXIT_SUCCESS;
 
}
 
int powervec(int coef, int expo, vector<int> &chamber)
 /* Since this function clearly does not cope with negative exponents 
   it might be better to have expo as an unsigned or at least 
   check that it is >= 0 */
{
    int total = 1;
 
    for(int num = 0; num != expo; num++)
    {
        total *= coef;
        chamber[num] = total;
    }
 
    return total;
 
}
 

[Banfa]

After a bit of research I find that rather than

    int x;
 
    while(!(cin >> x))
    {
        cout << "\n!!!invalid input received!!!\n\nTry again...\n\n";
    }
 

you may find this more reliable

    char input[100];
    int x;
    char *pEnd;
 
    do
    {
        cin.getline( input, sizeof input );
 
        x = (int)strtol(input, &pEnd, 10);
 
        if (!x)
            cout << "\n!!!invalid input received!!!\n\nTry again...\n\n";
    }
    while(!x);
 

[de_mystiX]

Oi Bantfa!

That rocks...thanks a lot, bro :)

My programming style has totally been impacted in a very positive way

I'm more proficient with selective execution

The way I go about planning is more practical

dude, thank you thank you thank you

just what i needed to here :D