c++ string.length() and casting string to char arrays not working properly?

Question

I'm writing a program that takes in a user's string and prints out the occurrences of each letter. For some reason when I try to take the length of the string, it cuts out whatever is after a white space.

For example: you enter "hello world" and the length is 5, but if you entered "hello_world" the length is 11.

Also when trying to store the string to an int array it only stores whatever is before a white space. Anyone know what I'm doing wrong?

#include <iostream>
#include <string>
#include <sstream>
#include <algorithm>
#include <cstdlib>
#include <cstring>

using namespace std;

int main()
{
    //prototypes
    void display_results(int a[]);
    void compute_letter_count(int a[], string s);

    //get user input for string
    string usr_string;
    cout << "Enter string: ";
    cin >> usr_string;

    //delete all non letter characters?

    //get length of string
    int length_string = usr_string.length();
    cout << "the length is: " << length_string << endl;

    //sort string in alphabetical order
    sort(usr_string.begin(), usr_string.end());

    //cout << usr_string;
    //convert string to array of chars
    const char *s = usr_string.c_str();

    //create in array to convert char array to int array
    int array[length_string];

    //loop to change each index in usr_string to int in array
    for (int i = 0; i < length_string; i++)
    {
        static_cast <int> (usr_string[i]);
        array[i] = usr_string[i];
        cout << array[i];
    }

    //cout << (int) usr_string[1];
    return 0;
}

void display_results(int a[])
{
    //for (int i = 0; i < 26; )

}

void compute_letter_count(int a[], string s)
{

    //
}