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Corrected Swap

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Pointers, Arrays, and Recursion

4.5（182 个评分） | 14K 名学生已注册

课程 3（共 4 门，Introduction to Programming in C 专项课程）

The third course in the specialization Introduction to Programming in C introduces the programming constructs pointers, arrays, and recursion. Pointers provide control and flexibility when programming in C by giving you a way to refer to the location of other data. Arrays provide a way to bundle data by guaranteeing sequences of data are grouped together. Finally, recursive functions—functions that call themselves—provide an alternative to iteration that are very useful for implementing certain algorithms.

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4.5（182 个评分）

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RS

Jan 24, 2019

Very well designed hands-on training course for developing a real software program in C.

VT

Apr 22, 2020

very informative and helpful quizzes, readings, and videos

从本节课中

Pointers

Pointers are one of the most important and powerful aspects of the C language. Pointers are critical to understanding arrays, which let you manipulate sequences of data. They also give a programmer control and flexibility when programming, enabling solutions that are clean and efficient. Some other languages use pointers implicitly—or pointer-like constructs—so understanding their use will make you a better programmer in any language.

Corrected Swap2:38

教学方

Andrew D. Hilton
Associate Professor of the Practice
Anne Bracy
Senior Lecturer
Genevieve M. Lipp
Assistant Professor of the Practice
Liz Wendland

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脚本

In this video, we're going to examine and step through a swap function that was written with pointers. Previously, we looked at a swap function that was written without pointers that didn't actually work. This one does and it's been written slightly differently. First, let's examine the differences. The first thing you'll notice is that swap takes two arguments, x and y which are pointers to integers. You'll see here, that we have written and int star then a space then an x, and an int star then a space and then a y. You could also write it in the following way with the x right next to the star. Both of these are correct and you'll see both when you look at C code. Now, x and y are pointers to integers. So, as we access the values of the integers that x and y point to in the code inside swap, we're going to have to de-reference x and y. And so, that's why we'll see these stars in front of x and y throughout the code. The final difference is how you call this function. In the main, instead of passing in a and b, we now have to pass in the address of a and the address of b. So, let's step through this function. We begin in the main. We have a variable a and a variable b, that have initial values three and four. Now, when we call the swap function instead of passing in three and four as we did in the previous version of this function, we now need to pass in the address of a and the address of b. So, we're going to create variables x and y, and x will point back to a and y will point back to b. Let's step into the function. We're going to mark the call site location 1 and hop into the swap function. Inside of swap, we're going to make a new variable called temp and that's where we're going to temporarily store the value that x points to, which is the value of a, which is three. Now, we can take the value that y points to which is the value of b or four and store that in the value that x points to, namely the variable a. Finally, we're going to take the temporary variable three and store that into the integer that y points to, which is the variable b. When we step out of the function, we see that our original variables a and b have indeed been swapped. So, when we execute the print statement, we now have a equals four and b equals three which is what we were expecting to have from a correctly working swap function.

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