Control conditions are the basic building blocks of C programming language. In this tutorial, we will cover the control conditions through some easy to understand examples.
There are two types of conditions :

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• Decision making condition statement
• Selection condition statement

Let’s understand these two types with the help of examples.

Decision making condition statement

Conditions like ‘if’, “if-else”, “if-else-if”, “nested if”, ternary conditions etc fall under this category.

1. If Condition

This is basic most condition in C – ‘if’ condition. If programmer wants to execute some statements only when any condition is passed, then this single ‘if’ condition statement can be used. Basic syntax for ‘if’ condition is given below:

Now, we should have working program on ‘if’ condition.

Output for above program is given below.

In above program, programmer wanted to exit from program if two command line arguments are not passed to program. We can see if program executable is run without any argument, message is displayed on console and program exited.

2. If-Else Condition

This is two-way condition in C – ‘if-else’ condition. If programmer wants to execute one set of statements on success case of one condition and another set of statements in all other cases, then ‘if-else’ condition is used. Either ‘if’ case statements are executed or ‘else’ case statements are executed. Basic syntax for ‘if-else’ condition is given below:

Adobe cloud pricing for mac download. Now, given below is very basic program that has been made for checking number is even or odd, it is for understanding usage of ‘if-else’ condition.

Output:

In above program, programmer wanted user to enter number which is checked in condition whether it is divisible by 2. If condition is true, number is displayed “EVEN”, otherwise number is displayed “ODD”.

3. Ternary Operator

There is alternative to ‘if-else’ condition which is ternary operator that is different syntax but provides functionality of ‘if-else’ condition. Basic syntax of ternary operator is given below:

For example,

Output:

4. If-Else-If condition

This is multi-way condition in C – ‘if-else-if’ condition. If programmer wants to execute different statements in different conditions and execution of single condition out of multiple conditions at one time, then this ‘if-else-if’ condition statement can be used. Once any condition is matched, ‘if-else-if’ condition is terminated. Basic syntax for ‘if-else-if’ condition is given below:

Now, given below is very basic program that has been made for mapping user-input color with fruit, it is for understanding usage of ‘if-else-if’ condition.

Output:

In above program, programmer wanted user to enter color (out of red/green/yellow as indicated), then input color is compared first with red in ‘if condition’, then compared with ‘else-if’ conditions. Here, it is noted that once any condition is matched, ‘if-else-if’ condition terminates. Here, if no ‘if’ or ‘else if’ is matched, then at last ‘else’ condition is executed which we can see in above output when invalid color is input.

5. Nested-If conditions

This is nested if or if-else or if-else-if conditions in C. Basic syntax for nested ‘if’ or ‘if-else’ condition is given below:

Output:

In above program, nested if conditions are used. It is always safer to have NULL check on pointer before accessing it (More on C pointers here).

In the above code snippet, example is taken for double pointer. The first ‘if’ condition is to check double pointer (i.e. ** double_ptr) is non-NULL, then only, move ahead to access inner pointer (i.e. ptr). If double pointer is non-NULL, then only nested ‘if’ condition is checked whether inner pointer is NULL or not. If nested ‘if’ condition is OK, then it is safe to access value at pointer.

Selection condition statement

6. Switch case conditions

Switch case is clean alternative of ‘if-else-if’ condition. Here, several conditions are given in cases that facilitates user to select case as per input entered. Basic syntax for using switch case statement is given below.

It is noted that any statement between switch statement and first case statement is dead code which is never executed. For understanding ‘switch’ case, basic program is created in which basic arithmetic operation on two numbers is done as per input entered by user. Several cases of arithmetic operations are handled in switch cases. Basic program using ‘switch case’ is given below.

Output:

In above program, user is given basic menu with operations allowed in program. User is asked to enter initial character of displayed operations. User is asked to enter two numbers also on which selected arithmetic operation would be performed. After all input from user, program checks input with switch cases and executes statements under matched switch case; since break statement is there so only statements under matched case are executed.

Note that if break statement is not given in cases and any case is matched, then statements of below cases would also get executed even though below cases condition is not matched. We can understand this in given below output. Here, as per code, if ‘x’ is entered, then case ‘x’ is executed and there is no break statement so all cases below case ‘x’ are executed without any condition check on below cases.

If you do not backup your server regularly, you have almost no way of restoring lost files. As a result, backup copies should always play an important role in your server planning. The rsync synchronization tool/protocol is one of the many backup solutions available.

1. 5 popular rsync backup scenarios

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What is rsync, and what is it used for?

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The name rsync refers to a network protocol for file synchronization developed in 1996 by Andrew Tridgell (among others), who headed up the SAMBA project. In addition to the protocol, there is a tool of the same name that facilitates communication over the protocol. The GPL-licensed application can be used free of charge and transfers files from a source directory to the required target directory – locally or via a public network. The file size and creation time of all files in the source and target folders are compared during syncing, so that each sync process only copies changed files. For this reason, the rsync backup process is called an incremental backup variant, which offers the advantage that backups are fast and take up little storage space.

rsync is available for all standard UNIX operating systems like OS/2, Linux or macOS. Using the API wrapper Cygwin, it can also be used on Microsoft Windows.

Typical use scenarios for rsync include data backups and generation of mirror servers (complete server images) as well as data synchronization in companies with various locations and weak data connections. In particular, the latter function is almost exclusively performed by modern cloud technologies today – also because weak data connections are becoming increasingly rare.

Overview of the most important rsync options

The outstanding feature of rsync backups is their efficiency. The incremental approach minimizes network utilization, which is an advantage for large files in particular – regardless of whether the changes to the files are major or minimal. As a command line tool, rsync is controlled via the Terminal by default – or via the Command Prompt, if you use rsync on a Windows device. The entries have the following syntax:

As a source and target path, you specify the respective start directory and the directory where you want rsync to save the backup copy. You can define individual settings for your rsync backups using the options, which are either abbreviated to letters or written out. The table below summarizes the most important parameters that can be combined with one another:

Setting up an rsync backup on Linux servers

To use rsync on Linux operating systems, install the protocol in the package of the same name and create your backups using Terminal commands. Alternatively you can use applications like Back In Time, rsnapshot (for regular automated backups) or Unison to control the backup process via a graphical user interface. In the example below using Ubuntu, we show you the most important steps to set up backup processes using rsync:

rsync is installed by default under Ubuntu. If this is not the case, install it using the following command.

When rsync is installed, use the required Terminal commands to specify the source and target directories and the backup options. For example, you can run the standard mode (“Archive”) as follows:

It is advisable to use the test run (-n) and check the accuracy of the parameters and directories specified; inaccurate specifications can result in data losses in a worst case scenario. If some files are not copied as required during the process, this is often due to missing access rights. In cases like this, try running the command as an administrator by prefacing it with the “sudo” parameter.

5 popular rsync backup scenarios

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Once you know the fundamental commands, rsync is an outstanding tool for copying files and making backups. You can either test and apply individual command setups or use proven combinations of the available rsync parameters. For example, the following rsync backup scenarios are particularly popular:

Standard backup with archival mode

The archival mode, which copies all files from the source directory to the target directory (including all sub-directories) and retains all authorizations, time stamps and device data, is the ideal and simplest solution in many cases as it combines various options in a single parameter. If you combine the mode with the –v parameter, you will also receive comprehensive status information during the backup process.

Identical copy of the source directory

Not only can rsync transfer files from A to B, it can also make identical copies of folders or entire directories. After standard archival, the files that were in the target folder before rsync, but are not in the source folder, are deleted.

Backup excluding files of a specific format

If you want to run a backup excluding files in a specific format, you can use the --exclude command to do so. The parameter allows you to define an individual character pattern, that rsync uses as an indicator to ignore a file. The following sample code excludes text files .txt.

Backing up files with a defined minimum or maximum size

If you don’t want a specific character pattern, but the file size to influence exclusion of specific files in an rsync backup, you can use the --max-size and --min-size parameters. If you use the following command, only files of at least 10 MB and at most 100 MB are copied:

Backup including character format conversion

You may have to convert files into a different character format in the target directory – for example if you want to transfer data from a Mac to a Linux server. As standard, Apple devices use UTF8-MAC, which is not available on Linux systems and would cause problems with special characters and umlauts. The --iconv option lets you easily adapt the character encoding as part of the rsync backup process (from UTF8-MAC to UTF8 in the example):