Printing out a diceplot histogram - c++

Question

When I complie and run my code I get the same output everytime despite having a random function. It defaults to the trial output shown on the assignment guide. I've tried to alter what's inside the print_histogram however each time I get the message in terminal that says I haven't declared "blank".
// ============================================================================
// diceplot.cpp
//
//
// ============================================================================
#include <iostream>
#include <cstdlib>
using namespace std;
// Prototype/define functions anywhere below
//loop that rolls dice and returns the dice number
int roll() {
int dice = rand() % 6 + 1;
return dice;
}
//loop that arranges the numbers and prints it out starting from index
void print_histogram(int list[], const int number_rolls){
for (int count = 0; count < number_rolls; count++){
cout << "\n" << count + 4 << ": ";
for (int index = 0; index < list[count]; index++){
cout << "X";
}
}
}
//given code
int main() {
int seed, n;
cout << "Enter a positive interger: " << endl;
cin >> seed >> n;
// Seed the pseudo-random number generator for repeatable results
srand(seed);
// Your code here
// keeps track of the outputs from the rolls
int list[21];
for (int count = 0; count < 21; count ++){
list[count] = count / 2;
}
//adds the roll of each experiment
int sum = 0;
for(int count = 0; count < n; count++) {
int dice_1 = roll();
int dice_2 = roll();
int dice_3 = roll();
int dice_4 = roll();
sum = dice_1 + dice_2 + dice_3 + dice_4;
if (sum == 21){
list[25 - 4]++;
break;
}
}
// prints out the histogram
print_histogram(list, 21);
return 0;
}

Answer 1

I copied the code you posted, formatted it, removed all of the comments, and then added my own comments:
#include <iostream>
#include <cstdlib>
using namespace std;
int roll() {
int dice = rand() % 6 + 1;
return dice;
}
void print_histogram(int list[], const int number_rolls) {
for (int count = 0; count < number_rolls; count++) {
cout << "\n" << count + 4 << ": ";
for (int index = 0; index < list[count]; index++) {
cout << "X";
}
}
}
int main() {
int seed, n;
cout << "Enter a positive interger: " << endl;
cin >> seed >> n;
// Here srand is called which does indeed seed the calls to rand. However,
// that doesn't change your output because your output is not showing
// anything that has to do with rand being called
srand(seed);
// This has exactly 21 elements, not n elements. Not sure if that was
// something you wrote or a default from your assignment
int list[21];
for (int count = 0; count < 21; count++) {
// This right here is what your histogram is currently showing. There
// is nothing random here, the value is the same every time
list[count] = count / 2;
}
int sum = 0;
for (int count = 0; count < n; count++) {
int dice_1 = roll();
int dice_2 = roll();
int dice_3 = roll();
int dice_4 = roll();
sum = dice_1 + dice_2 + dice_3 + dice_4;
// I don't know why the condition exists. As the code is currently
// written the dice rolls essentially have a chance to add up to 21 and
// cause the code inside the if statement to be executed
if (sum == 21) {
// 25 minus 4 is 21. Writting to index 21 is out of bounds because
// list only has 21 elements. This is undefined behavior
list[25 - 4]++;
break;
}
}
print_histogram(list, 21);
return 0;
}
I would suggest removing this section:
for (int count = 0; count < 21; count++) {
// This right here is what your histogram is currently showing. There
// is nothing random here, the value is the same every time
list[count] = count / 2;
}
... and replacing it with code that sets all elements of list to 0. Later on in the for loop responsible for rolling the four dice you can increment elements of list based on what the sum of the rolls are
Get rid of this:
if (sum == 21) {
// 25 minus 4 is 21. Writting to index 21 is out of bounds because
// list only has 21 elements. This is undefined behavior
list[25 - 4]++;
break;
}
... and replace it with code that increments the appropriate element of list regardless of what the value of sum is