Introduction
In C, programs are composed of statements. These statements are terminated with a semi-colon, and are collected in sections known as functions. By convention, a statement should be kept on its own line, as shown in the example below:
#include <stdio.h> int main(void) { printf("Hello, World!\n"); return 0; }
#include <stdio.h> int main(void) {printf("Hello, World!\n");return 0;}
This book is going to focus on the above piece of code, and how to improve it. Please note that during the course of the tutorial, there will be many (apparently) redundant pieces of code added. These are only added to provide examples of techniques that we will be explaining, without breaking the overall flow of code that the program achieves.
Line Breaks and Indentation
The addition of white space inside your code is arguably the most important part of good code structure. Effective use of white space can create a visual scale of how your code flows, which can be very important when returning to your code when you want to maintain it.
Line Breaks
| Note that we have used line numbers here; they are not a part of the actual code. They are only there for reference in this book. |
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#include <stdio.h> -
int main(void){ int i=0; printf("Hello, World!"); for (i=0; i<1; i++){ printf("\n"); break; } return 0; }
#include <stdio.h> int main(void) { int i=0; printf("Hello, World!"); for (i=0; i<1; i++) { printf("\n"); break; } return 0; }
Blank Lines
Blank lines should be used to offset the main components of your code. Use them- After precompiler declarations.
- After new variables are declared.
- Between lines 1 and 2, because line 1 has a preprocessor directive
- Between lines 4 and 5, because line 4 contains a variable declaration
The following lines of code have line breaks between functions, but without indentation.
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#include <stdio.h> -
int main(void)
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{ -
int i=0;
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printf("Hello, World!");
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for (i=0; i<1; i++)
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{ -
printf("\n");
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break;
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} -
return 0;
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}
Indentation
Many text editors automatically indent appropriately when you hit the enter/return key.
Although adding simple line breaks between key blocks of code can make code easier to read, it provides no information about the block structure of the program. Using the tab key can be very helpful now: indentation visually separates paths of execution by moving their starting points to a new column in the line. This simple practice will make it much easier to read and understand code. Indentation follows a fairly simple rule:- All code inside a new block should be indented by one tab more than the code in the previous path.
- Lines 5 to 13
- Lines 10 and 11
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#include <stdio.h> -
int main(void)
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{ -
int i=0;
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printf("Hello, World!");
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for (i=0; i<1; i++)
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{ -
printf("\n");
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break;
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} -
return 0;
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}
Indentation was originally one tab character, or the equivalent of 8 spaces. Research since the original indent size has shown that indents between 2 to 4 characters are easier to read, resulting in such tab sizes being used as default in modern IDEs. However, an indent of 8 characters may still be in use for some systems.
Comments
Comments in code can be useful for a variety of purposes. They provide the easiest way to set off specific parts of code (and their purpose); as well as providing a visual "split" between various parts of your code. Having a good comments throughout your code will make it much easier to remember what specific parts of your code do.Comments in modern flavors of C (and many other languages) can come in two forms:
//Single Line Comments (added by C99 standard,famously known as c++ style of comments)/*Multi-Line Comments*/ (only form of comments supported by C89 standard)
This section is going to focus on the various uses of each form of commentary.
Single-line Comments
Single-line comments are most useful for simple 'side' notes that explain what certain parts of the code do. The best places to put these comments are next to variable declarations, and next to pieces of code that may need explanation.Based on our previous program, there are two good places to place comments
- Line 3, to explain what 'int i' is going to do
- Line 11, to explain why there is a 'break' keyword.
#include <stdio.h> int main(void) { int i=0; // loop variable. printf("Hello, World!"); for (i=0; i<1; i++) { printf("\n"); break; //Exits 'for' loop. } return 0; }
Multi-line Comments
Single-line comments are a new feature, so many C programmers only use multi-line comments.
Multi-line comments are most useful for long explanations of code. They can be used as copyright/licensing notices, and they can also be used to explain the purpose of a block of code. This can be useful for two reasons: They make your functions easier to understand, and they make it easier to spot errors in code. If you know what a block is supposed to do, then it is much easier to find the piece of code that is responsible if an error occurs.As an example, suppose we had a program that was designed to print "Hello, World! " a certain number of times, a specified number of times. There would be many for loops in this program. For this example, we shall call the number of lines i, and the number of strings per line as j.
A good example of a multi-line comment that describes 'for' loop i's purpose would be:
/* For Loop (int i)
Loops the following procedure i times (for number of lines). Performs 'for' loop j on each loop,
and prints a new line at end of each loop.
*/Similarly, you should always include a multi-line comment before each function, to explain the role, preconditions and postconditions of each function. Always leave the technical details to the individual blocks inside your program - this makes it easier to troubleshoot.
A function descriptor should look something like:
/* Function : int hworld (int i,int j)
Input : int i (Number of lines), int j (Number of instances per line)
Output : 0 (on success)
Procedure: Prints "Hello, World!" j times, and a new line to standard output over i lines.
*/Finally, if you like to have aesthetically-pleasing source code, the multi-line comment system allows for the easy addition comment boxes. These make the comments stand out much more than they would without otherwise. They look like this.
/***************************************
* This is a multi line comment
* That is nearly surrounded by a
* Cool, starry border!
***************************************/#include <stdio.h> int main(void) { /************************************************************************************ * Function: int main(void) * Input : none * Output : Returns 0 on success * Procedure: Prints "Hello, World!" and a new line to standard output then exits. ************************************************************************************/ int i=0; //Temporary variable used for 'for' loop. printf("Hello, World!"); /* FOR LOOP (int i) Prints a new line to standard output, and exits */ for (i=0; i<1; i++) { printf("\n"); break; //Exits 'for' loop. } return 0; }
A few programmers add a column of stars on the right side of a block comment:
/***************************************
* This is a multi line comment *
* That is completely surrounded by a *
* Cool, starry border! *
***************************************/Comments written in source files can be used for documenting source code automatically by using popular tools like Doxygen
