An algorithm in C is a set of well-defined instructions that are written in a specific order to solve a particular problem. It takes a set of input(s) and produces the desired output. An algorithm should be written in such a way that it can be used in different programming languages. It is not the entire program or code; it is simple logic to a problem represented as an informal description in the form of a flowchart or pseudocode.

Some key properties of an algorithm include:

• Input: The algorithm must have input(s) .
• Output: The algorithm must have output(s) .
• Finiteness: The algorithm must terminate after a finite number of steps.
• Definiteness: Each step in the algorithm should be clear and unambiguous.
• Effectiveness: Algorithms should be most effective among many different ways to solve a problem.

It is a good practice to write down the algorithm first before attempting to write a program. Each step of the algorithm will get converted to a line or a set of lines in the programming language. One of the common algorithms used in C is the sorting algorithm, which arranges a collection of items in a certain order, such as numerically or alphabetically.