Question

include 4 using name… # (What Does this Program Do?) What does the following program print? 1 // Exercise 4.22: ex04_22.cpp 2 // What does this program print? 3 #include 4 using namespace std; 5 6 int main() 7 { 8 int row = 10; // initialize row 9 int column; // declare column 10 11 while ( row >= 1 ) // loop until row < 1 12 { 13 column = 1; // set column to 1 as iteration begins 14 15 while ( column <= 10 ) // loop 10 times 16 { 17 cout << ( row % 2 ? "<" : ">" ); // output 18 ++column; // increment column 19 } // end inner while 20 21 --row; // decrement row 22 cout << endl; // begin new output line 23 } // end outer while 24 } // end main

Short answer

The program prints 10 lines. Each line contains 10 characters: '>' for even starting rows (10, 8, 6, ...) and '<' for odd starting rows (9, 7, 5, ...).

Step-by-step solution

- Understand the outer while loop

The outer while loop (lines 11-23) controls the rows and iterates as long as the variable 'row' is greater than or equal to 1. It starts with 'row' initialized to 10 and decreases it by 1 in each iteration after the inner loop completes (line 21).

- Examine the inner while loop

The inner while loop (lines 15-19) controls the columns within each row. It iterates 10 times as controlled by the variable 'column', which starts at 1 and is incremented until it surpasses 10. Upon completion, it restarts for the next row due to the outer loop.

- Analyze the output condition

For each iteration of the inner while loop, a character is printed (line 17). The printed character depends on the result of 'row % 2' which checks if the row number is odd (using the tertiary conditional operator, '?' ). If odd, it prints '<', otherwise it prints '>' for even row numbers.

- Recognize the line break

At the end of the inner loop, but still inside the outer loop, the program prints a newline character (line 22). This creates separate lines for each row.

Final Step - Predict the program output

This program will print 10 lines of output. Each line corresponds to a row and will contain either '<' or '>' symbols. Rows starting with an even number (including 10, the starting value) will be filled with '>', and rows starting with an odd number will be filled with '<'. Each line will have 10 of these characters.

Key concepts

C++ Loop Structures

Loop structures in C++ are fundamental constructs that allow programmers to execute a block of code repeatedly until a specified condition is met, or to iterate over elements in a sequence. The two types of loops demonstrated in our textbook exercise, the 'while' loop, and the nested 'while' loop, are perfect for situations where the number of iterations is not known beforehand, or it depends on a certain condition being true.
In the provided exercise, the outer 'while' loop checks if the variable 'row' is still greater than or equal to 1. If so, it executes the block of code within it, which includes another 'while' loop, also known as the inner loop. The inner loop iterates exactly 10 times, as it is controlled by the 'column' variable, which starts at 1 and increases with each iteration until it reaches 11, after which the loop terminates. Each pass through the inner loop outputs a character, and the outer loop handles the progression to the next row and a new line.
To optimize your understanding:

• Visualize loop constructs as a flowchart to see how the iteration works.
• Use debugging tools or insert print statements within the loops to observe the value of variables at different stages.
• Try modifying the loop conditions or the increment/decrement statements to see how it affects the program's behavior.

C++ Program Analysis

Program analysis involves a step-by-step review of code to understand what the program does, how it achieves its objectives, and what the expected output should be. Analyzing a C++ program like the one in this exercise involves understanding the control flow, recognizing the significance of each line of code, and predicting the output.
In our exercise, analysis begins with understanding the flow of the two nested 'while' loops. We must recognize that the inner loop prints characters depending on the current 'row' value, specifically it uses a conditional operator to decide whether to print '<' or '>'. We also note how loop control variables 'row' and 'column' change within each iteration.
Here's some advice on analyzing programs:

• Break down the code into smaller chunks and understand each part individually before trying to understand the full picture.
• Examine the role of conditional statements and iterate mentally through a few cycles of the loop with different values.
• Understand how nested loops work together. Know that the inner loop completes all its iterations for every single iteration of the outer loop.

C++ cout usage

The usage of 'cout' in C++ is for the standard output stream, often utilized to print data to the console. In our exercise, 'cout' is used to print characters on the screen within the inner loop. The conditional operator in conjunction with 'cout' prints either '<' or '>' based on the current 'row' value being odd or even, respectively.
Understanding 'cout' is essential for producing readable results and for debugging. In the context of the provided problem, 'cout' allows the visualization of the program's output pattern.
A few pointers on using 'cout' efficiently:

• Remember that 'cout' prints the content to the console immediately, which can be useful for tracking variable values during loops.
• Combine 'cout' with 'endl' to add a newline character, which helps in formatting the output and making it more readable, as seen in the example program.
• 'cout' can be used with different data types, and it can also be chained using the '<<' operator to print multiple items with a single statement.