need help to enhence this program

[lucan74]

Hi,
the code below is a simple program. this is my question and problem
1: how to disallow the user to input char or string?
2: disallow the user to enter a neg number.

Thanks in advance.

#include <iostream>
#include <math.h>

using namespace std;

float apple;
float orange;
float pear;
float choice;

float cost ()
{
    //to calculate the ammo needed
    apple = choice * 16;
    orange = choice * 40;
    pear = choice *6;
    cout << endl;
    cout << "You will need\n" << apple << " to buy apple.\n" << endl;
    cout << "You will need\n" << orange << " to buy orange.\n" << endl;
    cout << "You will need\n" << pear << " to buy pear.\n" << endl;
    return 0;
}

int main()
{
    //title for the user.
    //also telling the user how to end the program.
    cout << "\n\tThis is a program that calculate numbers" << endl;
    cout << "\n\tEnter 0 to exit." << endl;
    while (1)
    {
        cout << "\nEnter a number? : ";
        cin >> choice;
        if (choice != 0)
        {
            cost ();
        }
        else
        {
            cout << "You are ending this session." << endl;
            break;
        }
    }
    return 0;
}

[condor]

Please see the functions: int isdigit ( int c ), int isalpha ( int c ) and change the test in line 34.

[keskiverto]

Where do we start?

First, do not use global variables. It is a bad habit.

Second, comparing a float against 0 is risky, because floats are internally stored as discrete binary values. Weird things will bite you, if you think that floats behave as in math.

Why does cost() return a float? void is a valid return type.

Why floats in general?


isdigit() can tell you whether a character that you have is a digit. cin >> into a float stores nothing, if user types something else. However, cin will have failbit set.

if ( cin.good() && 0.0f < choice ) ...
else break;

Now the loop continues as long as the user types positive numbers. Remember, that if !cin.good(), then cin remains in non-good state after the loop, and should be cleared before next use.

[lucan74]

#include <iostream>
#include <math.h>

using namespace std;

float cost ()
{
    //to calculate the ammo needed
    float apple;
    float orange;
    float pear;
    apple = choice * 16;
    orange = choice * 40;
    pear = choice *6;
    cout << endl;
    cout << "You will need\n" << apple << " to buy apple.\n" << endl;
    cout << "You will need\n" << orange << " to buy orange.\n" << endl;
    cout << "You will need\n" << pear << " to buy pear.\n" << endl;
    return 0;
}

int main()
{
    //title for the user.
    //also telling the user how to end the program.
    cout << "\n\tThis is a program that calculate numbers" << endl;
    cout << "\n\tEnter 0 to exit." << endl;
    float choice;
    while (1)
    {
        cout << "\nEnter a number? : ";
        cin >> choice;
        if (choice != 0)
        {
            cost ();
        }
        else
        {
            cout << "You are ending this session." << endl;
            break;
        }
    }
    return 0;
}

i have change the code and remove all global variables. and when i run the code, i this what i get

Compiling: main.cpp
D:\programming\C++\test1\main.cpp: In function 'float cost()':
D:\programming\C++\test1\main.cpp:12: error: 'choice' was not declared in this scope
Process terminated with status 1 (0 minutes, 0 seconds)
1 errors, 0 warnings

in this case where should i place "choice"?
thanks.

[condor]

change line 6:

float cost (float choice)

and line 35 as follows:

cost(choice);