Program crashing in C++

Question

I am just starting to learn C++ and this is a program I'm writing for an exercise:

#include <iostream>
#include <string>
using namespace std;

int main ()
{
    int uppercase=0, lowercase=0, digits=0, other=0, i=0;
    int character;
    char* string;
    cout << "Enter a string!\n";
    cin.getline(string, 20); 

    while(true)
        {
        character = int(*(string+i));
        if (character==0)
            {
            break;
            }
        if (character > 64 && character < 91)
            {
            uppercase++;
            }
        if (character > 96 && character < 122)
            {
            lowercase++;
            }
        if (character > 47 && character <58)
            {
            digits++;
            }
        else
            {
            other++;
            }
        i++;
        }

    cout << "Upper case " << uppercase << "\n";
    cout << "Lower case " << lowercase << "\n";
    cout << "Digits " << digits << "\n";
    cout << "Others " << other << "\n";

    return 0;
}

The program crashes after it finishes printing the results. Am I missing something really obvious here?

Side question: The variable 'other' is always increased even if it shouldn't be. Am I using the else statement wrong?

Answer 1

You have not allocated memory for string

Try this (allocate on stack):

char string[256];

or (allocate on heap):

char* string = new char[256];

delete[] string;

UPDATE

Using std and predefined isdigit(), isalpha(), etc, the code can be rewritten as follows:

#include <iostream>
#include <string>

int main ()
{
    int uppercase=0, lowercase=0, digits=0, other=0;

    std::cout << "Enter a string!\n";

    std::string myline;
    std::getline(std::cin, myline);

    for (std::string::iterator i = myline.begin(); i != myline.end(); ++i)
    {
        if (isdigit(*i))
        {
            digits++;
        }
        else if (isalpha(*i))
        {
            isupper(*i) ? uppercase++
                        : lowercase++;
        }
        else
        {
            other++;
        }
    }

    std::cout << "Upper case " << uppercase << "\n";
    std::cout << "Lower case " << lowercase << "\n";
    std::cout << "Digits " << digits << "\n";
    std::cout << "Others " << other << "\n";

    return 0;
}