Tracing a asterisks triangle program

This is a discussion on Tracing a asterisks triangle program within the C Programming forums, part of the General Programming Boards category; Code: # include <stdio.h> void printTriangle(int num_rows) { int currentRow; int currentStar; for(currentRow = 0; currentRow < num_rows; currentRow++) { ...

  1. #1
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    Tracing a asterisks triangle program

    Code:
    # include <stdio.h>
    
    void printTriangle(int num_rows)
            {
                    int currentRow;
                    int currentStar;
                    for(currentRow = 0; currentRow < num_rows; currentRow++)
                    {
                            for(currentStar = 0; currentStar <= currentRow + (currentRow / 3 ); currentStar++)
                            {
                                    printf("*");
                            }
    
                            printf("\n");
                    }
            }
    
    int main()
    {
        printTriangle(5);
    
        return 0;
    }
    On Line 9, Why must there be an integer division of current_row and 3? Can anyone elaborate on this concept please?

  2. #2
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    Learning to follow a program step by step is a vital skill when you're trying to master the concepts.

    Let's look at the inner loop.

    Code:
    /* loop 1 */
    currentRow = 0
    
    currentStar <= currentRow + (currentRow / 3 )
    
    This is how many stars you want to print on the first loop.
    currentRow + (currentRow / 3 ) = 0 + 0/3 = 0 + 0 = 0
    Because of the "<=", you will print one star.
    
    /* loop 2 */
    currentRow = 1
    
    currentStar <= currentRow + (currentRow / 3 )
    
    currentRow + (currentRow / 3 ) = 1 + 1/3 = 1 + 0 = 1
    Two stars will be printed.
    
    /* loop 3 */
    currentRow = 2
    
    currentStar <= currentRow + (currentRow / 3 )
    
    currentRow + (currentRow / 3 ) = 2 + 2/3 = 2 + 0 = 2
    Three stars will be printed.
    
    /* loop 4 */
    currentRow = 3
    
    currentStar <= currentRow + (currentRow / 3 )
    
    currentRow + (currentRow / 3 ) = 3 + 3/3 = 3 + 1 = 4
    Five stars will be printed.
    
    etc...
    Notice that this is not a perfectly stepped printout, as dictated by the logic.

    Also remember that integer division truncates the result, which is why "currentRow/3" produces zero when "currentRow" is 0, 1, and 2.
    Last edited by Matticus; 12-06-2012 at 08:39 PM.

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    Matticus strikes again! Thank you!

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    You're very welcome! And I just correct an error in my post - for the last case, I accidentally had "Four stars will be printed."

  5. #5
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    > On Line 9, Why must there be an integer division of current_row and 3? Can anyone elaborate on this concept please?
    You could
    change it to /2, run the code and observe the changes to the output.
    change it to /4, run the code and observe the changes to the output.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    You could also note that the number of stars to be printed on each row, equals the current row number + 1.

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