How can you get a "x" element from rand()? - c++

Question

I have a rand number generator.
Now my question is how do I get for instance the first/second/third/fourth digit of the generated random number.
Implementing this so the user can use a hint when guessing the number.
example: result(rand): 9876
print hint 1: second number 8
print hint 2: fourth number 6
Whats the best way to tackle this? I've been thinking to convert the string to an char array in order to print out the certain locations where the values are being kept but that won't work I guess.
Correct me if my way of asking this questions is very bold.
int nummer = 4;
std :: string result = "";
for (int i = 0; i < nummer; i++)
{
result.push_back(rand()%10 + '0');
}

Answer 1

You have two options for solving this problem:
Create one random number between 0 and 9999 and then calculate the individual digits.
Create four random numbers between 0 and 9 which represent the individual digits and then, if necessary, calculate the whole number from the individual digits.
Normally, doing option #1 would be more straightforward. You seem to be going for option #2. Both ways are possible and which one is better probably depends on whether your program works more with the number as a whole or with individual digits.
If you decide to do option #2, then the question arises whether you want to work with ASCII character codes between '0' and '9' (i.e. codes between 48 and 57) or with actual numbers between 0 and 9. Normally, it is a bit easier to work with the actual numbers instead of ASCII character codes, but both ways are feasible.
Personally, I would solve it the following way:
#include <iostream>
#include <cstdlib>
#include <ctime>
int main()
{
//seed random number generator
std::srand( std::time(nullptr) );
//note that NUM_DIGITS should not be set so high
//that MAX_NUMBER is not representable as an `int`
constexpr int NUM_DIGITS = 4;
//set this to the highest possible number that
//corresponds to NUM_DIGITS
constexpr int MAX_NUMBER = 9999;
//this variable holds the entire number
int random;
//this array holds the individual digits
int digits[NUM_DIGITS];
///generate the random number
random = std::rand()%(MAX_NUMBER+1);
//calculate the individual digits of the random number
int remaining = random;
int divisor = (MAX_NUMBER+1) / 10;
for ( int i = 0; i < NUM_DIGITS; i++ )
{
digits[i] = remaining / divisor;
remaining = remaining % divisor;
divisor/= 10;
}
//print the whole random number
std::cout << "Whole random number:\n" << random << "\n\n";
//print the individual digits
std::cout << "Individual digits:\n";
for ( int i = 0; i < NUM_DIGITS; i++ )
{
std::cout << digits[i] << "\n";
}
}
Sample output (actual output depends on random number seed):
Whole random number:
8695
Individual digits:
8
6
9
5
I've been thinking to convert the string to an char array but that won't work I guess.
I see no reason to do this. In your posted code, you can simply write
result[0]
result[1]
result[2]
result[3]
to access the individual digits of the number.
In that respect, converting a std::string to a C-style character array has no advantages.

Answer 2

The code you've written is fine.
Whether you store the characters in an array or a string, you can access the elements using result[i] where i starts at 0.
I've been thinking to convert the string to an char array but that won't work I guess.
Using std::string is usually a better idea - still possible but a little harder to screw them up, and they're more powerful generally, but you could use a char array if you wanted:
char result[] = "0000"; // will have null terminator
for (int i = 0; i < 4; ++i)
result[i] = rand() % 10 + '0';
Letting result be a 5-character array - with a null terminator - means you can still print all four digits easily with std::cout << result.
Alternatively, you could pick a random 4-digit number and convert it to a string of a particular width, using '0's to pad:
#include <iostream>
#include <iomanip>
int main() {
std::ostringstream oss;
oss << std::setw(4) << std::setfill('0') << rand() % 10000;
std::cout << '[' << oss.str() << "]\n";
}