Lecture 8: Preview of Functions
Tuesday, September 27, 2011 Status: preliminary[
Up]
[Previous Lecture]
[Next Lecture]
Powerpoint Slides: none
Reading Assigned: 3.1-3.2
Homework Due: Homework 3
Homework Assigned: Homework 4
Topics Covered:
- Math library functions (examples)
- Overview of functions calls
- Arguments and return values
- Function prototypes and header files (basic)
Programs Shown:
- This program uses some functions from the math library:
math1.c
To compile this program, you need to use the -lm flag:
gcc -Wall math1.c -lm
- This program calculates the area of a washer (the kind that you use with nuts and bolts, not the kind that cleans your clothes): washer1.c. To do so, it has to compute the area of a circle twice. We can put that computation in a separate function named circleArea().
- If we put the circleArea() function at the end of the file instead of the beginning, then we have to add a function prototype at the top: washer2.c.
-
Finally, the main program itself is actually a function. Strictly
speaking, main() returns an int value. This
tells the operating system if there was an error. In the third
version of the program, we fix up main():
washer3.c.
Now we can compile with the -Wall option and not
encounter any warnings or errors.
- If we used gcc -Wall on the buggy
scanf3a.c
program, we would have know about the mistake of
using %f instead of %lf.
DO NOT COPY THIS PROGRAM. IT IS DELIBERATELY BUGGY! - Another example, this program has a function that computes the
average of two values: avg1.c.
Yes, functions can have many input values (a.k.a. formal parameters).
- Here we mix things up and combine the circleArea function from above with the avg() function: avg2.c.