Program not running with Array during Initialization

Question

I'm just practicing using arrays. So my program consist of inputting numbers of data type double into the array and have them print out. Simple.

I only limited the numbers down to 4. So the array, num_List[3] is in the code. I've made sure to use the for loops properly for reading and printing out the result.

The first few times I tested the code. I realized that the 4th number in the array was in scientific notation, telling me that I forgot to initialize the array to 0, in this case 0.0, since I'm using double. So I put in this code.

for (index = 0; index <= 3; index++)
    num_List[index] = 0.0;

This code should have initialized the arrays of num_List to 0.0. However, when I tested this, nothing came up, after I inputted the 4 numbers. So I made a logical error here or it's something else with the for loop that's causing it to be trapped and not continue the execution.

I've read in the books about this particular way to initialize.

#include <iostream>
using namespace std;

int main() {
double num_List[3]; // These are my variables
int index;
//double num; // Ignore these two for now, for they are to be modified later on.
//double result;

cout << "This program will summarize the numbers you've inputted print out the result. \n";
cout << "And also print out the address of the 1st and 4th address in the array." << endl;
cout << "Please enter the four numbers to be summarized.";

for (index = 0; index <= 3; index++) { // I put this in after I realized my mistake of not initializing my arrays to 0.0.
    num_List[index] = 0.0;} // This is where the problem is, I think. 

for (index = 0; index <= 3; index++) // This reads in the user the input
    cin >> num_List[index];

cout << "The numbers you have inputted is:\n";

for (index = 0; index <= 3; index++) // This prints out the array.
    cout << num_List[index] << ", " << endl;

return 0;
}

If you focus on the aforementioned code, and try to compile it, you'll see that my code unfortunately doesn't continue on from there after you input 4 numbers, regardless of whether or type a number and space it up to 4 numbers, or input a number, press the enter key for those numbers. Most likely I've made a obvious mistake, but I'm having some trouble seeing it.

I use Code Blocks, so things are a little different compared to the Bloodshed C++ compiler I used to use to practice codes on.

Answer 1

double num_List[3];

This declares an array with 3 elements, indexed 0 through 2.

for (index = 0; index <= 3; index++)

This loops through 4 indices, 0 through 3. When you do something with num_List[3], you get undefined behavior. In your trial, the undefined behavior fortunately resulted in just some garbage output.