Execution of Nested Loops

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来自 Duke University 的课程

Programming Fundamentals

224 个评分

Duke University

Programming Fundamentals

224 个评分

课程 1（共 4 门，Specialization Introduction to Programming in C）

Programming is an increasingly important skill, whether you aspire to a career in software development, or in other fields. This course is the first in the specialization Introduction to Programming in C, but its lessons extend to any language you might want to learn. This is because programming is fundamentally about figuring out how to solve a class of problems and writing the algorithm, a clear set of steps to solve any problem in its class. This course will introduce you to a powerful problem-solving process—the Seven Steps—which you can use to solve any programming problem. In this course, you will learn how to develop an algorithm, then progress to reading code and understanding how programming concepts relate to algorithms.

从本节课中

Reading Code

In this module, you will learn to read code—this means you will be able to execute a piece of code by hand, and clearly illustrate what each statement does and what the state of the program is. Understanding how to read code is the only way to be sure you can write correct code. By the end of this module, you will be able to read and understand code with functions, conditional statements, iteration, and other fundamental techniques.

While Loops3:23

Equivalent For and While Loops2:17

Execution of Nested Loops3:35

Execution of Continue2:56

与讲师见面

Andrew D. Hilton
Assistant Professor of the Practice
Electrical and Computer Engineering
Genevieve M. Lipp
Adjunct Professor
Electrical and Computer Engineering/Mechanical Engineering
Anne Bracy
Senior Lecturer
Computer Science, Cornell University

In this video we have an example of nesting.

In function f we have a while loop with an if statement inside of it.

And inside of the if statement there is a for loop.

The important thing to remember with nesting is that there's

really nothing special about it.

We follow the same rules we've always see.

We being with our execution arrow at the start of main.

And the first thing we're going to do is call f, passing 3 for a, and 8 for b.

We create a frame, as always.

And we're going to remember where we're going to return, and

begin executing code inside of f.

Since a less than b is true, we're going to go inside the body of the while loop.

We print a equals 3, b equals 8.

And then we reach an if statement that checks if a mod 2 is 0.

Remember that percent is the mod operator,

which computes the remainder when you do division.

3 divided by 2 has a remainder of 1, so 3 mod 2 is 1.

a mod 2 is not zero, so this conditional expression is false, and

we skip over the if statement.

>> a++ increments a to 4, and b-- decrements b to 7.

Now we've reached the end of the while loop.

So we jump to back to the beginning, and test it's condition again.

a less than b is true, so we enter the body and print a=4, b=7.

Now when we look at a mod 2, 4 mod 2 is 0.

0 = 0 is true, so we enter the if statement.

Now we have a for loop.

It's going to declare an int i, and initialize it to the value of a.

So we make a box for i, and set it equal to 4.

We then test the condition of the for loop.

4 less than 7 is true, so we enter the body of the for loop.

We print i = 4.

Then we perform the increment statement assigning 5 to i,

and return to the begging of the loop.

We check the condition again.

5 less than 7 is true, so we enter the for loop again, we print i = 5.

Then we increment i to 6, and return to the beginning of the loop.

We repeat this process.

6 less than 7, print i = 6.

Increment i to 7, and return to the beginning.

This time, 7 less than 7 is false.

So we skip past the four loop, leaving the scope of i.

And continue executing.

We're now at the end of the if statement's body,

so we resume executing right after it.

We increment a to 5 and decrement b to 6, and now we're at the end of the y loop.

So we jumped back to the top.

A less than b is still true.

So we enter the body, we print a=5, b=6.

We check a mod 2.

5 mod 2 is 1, 1=0 is false, so we skip the if statement.

We increment a to 6 and decrement b to 5.

And return to the top of the while loop.

6 less than 5 is false.

So we skip over the body of the while loop, reaching the end of the function.

This causes us to return to main.

The only thing left in main is the return statement, so

we return 0 and exit the program.

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