C programming language - the basic algorithm
C language introduced in the previous two articles in the Getting Started program entry procedures 1 , entry procedures 2 , from the beginning of this article we will introduce the C programming language.
Today to introduce a characteristic and algorithm of algorithms.
The basic characteristics of the algorithm
Content algorithm contains two aspects: algorithm design and analysis of algorithms
Algorithm design is actually for a particular type of problem and design an implementation process. Algorithm has the following features:
- Finite nature
- Uncertainty
- feasibility
- Entry
- Export
That we are in the design of algorithms to meet the above mentioned characteristics. Of course, the algorithm is good and bad, then we how to measure the pros and cons of an algorithm do?
Algorithm analysis is in fact an algorithm to measure the pros and cons, usually analyzed from the following aspects:
- Correctness
- readability
- Robustness
- Time complexity and space complexity
Expression algorithm
In describing an algorithm commonly used methods are: natural language, a flowchart, NS, etc. FIG.
natural language
This easy to understand natural language expression, we pass a specific example to find out.
Demand: any input number 3, wherein the minimum number is obtained.
(1) define four variables are a, b, c, and min.
Different (2) the size of the input three numbers are assigned to a, b, c.
(3) determining whether a is less than b, is less than, min value will be assigned to a, b or the value of the assigned min.
(4) determines whether less than c min, is less than, is executed (5), or the value of c is assigned min.
(5) Output min.
The benefits of this way of expression is easy to understand, but when it comes to complex algorithms of natural language it is not very convenient.
flow chart
It is a flowchart of a frame number to represent the different properties of the various operations, performed by flow lines to indicate the direction of the algorithm. He is characterized by visual image, which is widely used.
The following figure illustrates the flowchart of symbols and meanings
There are three basic configurations flowchart, i.e., sequential structure, and selecting structure of the cyclic structure.
- Sequential structure: the structure is simple linear sequence structure
- Structure selection: Select structure is called the branch structure
- Loop structure: repeatedly perform a series of operations, know when termination condition is not satisfied.
Then we need above flowchart to say something
NS flow chart
NS is a flowchart of the entire algorithm written in a rectangular frame, eliminating the flow lines in the flowchart. Let's continue to see an example:
Demand: Enter a number to determine whether a prime number.
The basic characteristics and algorithms of representation of the algorithm to introduce over.
Past articles
C language learning portal 01
C language learning portal 02
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