6.5. Two-dimensional tables

A two-dimensional table is a table where you choose a row and a column and read the value at the intersection. A multiplication table is a good example. Let’s say you wanted to print a multiplication table for the values from 1 to 6.

A good way to start is to write a simple loop that prints the multiples of 2, all on one line.

Run the active code below, which uses a simple loop that prints the multiples of 2, all on one line.

#include <iostream> using namespace std; int main() { int i = 1; while (i <= 6) { cout << 2 * i << " "; i = i + 1; } cout << endl; return 0; }

The first line initializes a variable named i, which is going to act as a counter, or loop variable. As the loop executes, the value of i increases from 1 to 6, and then when i is 7, the loop terminates. Each time through the loop, we print the value 2*i followed by three spaces. By omitting the endl from the first output statement, we get all the output on a single line.

The output of this program is:

2   4   6   8   10   12

So far, so good. The next step is to encapsulate and generalize.

Q-2: What is a good name for the variable x, found in the code block below?

#include <iostream>
using namespace std;

int main() {
  int x = 1;
  while (x <= 6) {
    cout << 3 * x << "   ";
    x = x + 1;
  }
  cout << endl;
  return 0;
}

• counter
• Try again!
• loop variable
• Try again!
• Both a and b
• Correct!
• None of the above
• Try again!

Q-3: Currently, the code below prints all of the multiples of three on one line. How can you change the output so that each multiple prints on its own line?

#include <iostream>
using namespace std;

int main() {
  int x = 1;
  while (x <= 6) {
    cout << 3 * x << "  ";
    x = x + 1;
  }
  cout << endl;
  return 0;
}

• Change the first output statement to say cout << 3 * x << endl;
• The addition of the endl will print the multiples of three on separate lines.
• Change the first output statement to say cout << 3 * x << \n;
• A newline character must be used in conjunction with a string. In this case, we are outputting an integer. To use a newline character in this scenario you must use quotes around it. (ex. "\n")
• Change the second output statement to say cout << endl << endl;
• This would simply print out two new lines after all of the multiples have already printed on one line.
• This code already prints each multiple on its own line.
• This code prints all multiples out on one line.

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