A simple C program to transform input data to output data. (Time-series data) Purpose: Demonstration of C programming. Audience: Aspiring C or C++ Developers. Model: A simple signal processing example (an FIR Filter). Features: data types, control flow, floating point numbers, program input and output. Disclaimer: Nothing in this slideshow is novel. This topic has been covered countless times, and can easily be found on Wikipedia, Youtube, etc. Errors in the program or slides are my own. I used the Eclipse IDE and GNU gcc on Linux

1. Moving Average in C
C Program for a Moving Average Filter
Colin McAllister, 24/7/2017

2. Moving Average in C
 A simple C program to transform input data to
output data. (Time-series data)
 Purpose: Demonstration of C programming.
 Audience: Aspiring C or C++ Developers.
 Model: A simple signal processing example.
 Features: data types, control flow, floating point
numbers, program input and output.

3. Block Diagram of Filter

4. Data Types
 0,1 – Boolean constants (False,True)
 int – Signed integer
 unsigned int – Unsigned integer
 double – Floating point (real) number
 double x[t], y[t] – Arrays of data

5. C Language Features
 main() function
 Program input - scanf()
 Program output - printf()
 Control flow – A simple “while(True)“ loop
 Blocks of code – Bound by “{“ and “}“
 Data types – assignment (equals sign “=“)
 Floating point numbers – Average value

6. Integrated Development Environment

7. Hello World Template

8. First Draft of Program

9. Input and Output of Floating Point
Program Statements
puts("Moving Average"); /* output */
puts("Enter sample"); /* output */
scanf("%lf", &value_in); /* input */
printf("Input value %fn", value_in);
Terminal Window:
$ ./MovingAvg
Moving Average
Enter sample
12.34
Input value 12.340000

10. Calculate Average of Three Numbers
#define SAMPLES 3
double x[SAMPLES];
double value_in, avg;
int i;
int main(void) {
puts("Moving Average"); /* output */
printf("Enter %d samples:n", SAMPLES); /* output */
for(i=0; i<SAMPLES; i++)
{ scanf("%lf", &value_in); /* input */
x[2]=x[1];
x[1]=x[0];
x[0]=value_in;
avg = (x[0]+x[1]+x[2])/3.0;
printf("Average %fn", avg);
}

11. Calculate Average – Terminal Window
 $ ./MovingAvg
 Moving Average
 Enter 3 samples:
 1.0
 Average 0.333333
 2.0
 Average 1.000000
 4.0
 Average 2.333333

12. Shift Data and Calculate Average

13. Shift Data and Calculate Average (Detail)

14. Shift and Calculate – Terminal Window
 $ ./MovingAvg
 Moving Average, Window Size 3
 Enter many samples:
 2.0
 x 0.000000, y 0.666667
 2.0
 x 2.000000, y 1.333333
 2.0
 x 2.000000, y 2.000000
 0.0
 x 2.000000, y 1.333333
 0.0
 x 0.000000, y 0.666667
 0.0
 x 0.000000, y 0.000000

15. Your Questions or Comments?
Clip art from www.123rf.com

16. Coding Considerations
 Develop in your favourite IDE
 Fix compiler errors and warnings
 Use Debugger to step through code
 Make code modular – Use functions
 Port program from C to C++
 Use OOP features of C++
 Use modern containers and iterators
 Try different compilers or even languages

17. Application Considerations
 Applications: Read about FIR Filters
 Optimisation: Avoid shifting the data
 Optimisation: Replace double with int
 Generate test data using Trig functions
 Generate noisy test data using rand()
 Use filter to improve Signal/Noise ratio
 Frequency response of Low pass filter
 Plot graphs to visualise Filter operation