Lecture 5. Functions II. Functions with Arguments. CptS 121 Summer 2016 Armen Abnousi

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1 Lecture 5 Functions II Functions with Arguments CptS 121 Summer 2016 Armen Abnousi

2 Remember Functions break problems into smaller pieces Easier to read, test and maintain Functions allow to avoid repetition of a piece of code (can be called multiple times) Functions should be cohesive and loosely coupled Problem: Write a program that given the radius of a circle, computes its area and circumference

3 Int main() { main Function double area = 0.0, circ = 0.0; Remember Write a program that given the radius of a circle, computes its area and circumference area = computearea(); circ = computecirc(); } printf( area is: %f\n, area); printf( circ is: %f\n, circ); return 0; My program s scope assigned by the OS Name: Address: area 8 circ Content:??????????????????

4 Scope of a Function Each function gets a scope (a space in memory) Int main() { double area, circ; area = computearea(); circ = computecirc(); Scope for main function Scope for computearea function } printf( area is: %f\n, area); printf( circ is: %f\n, circ); return 0; Name: Address: 1 area 2 circ Content:?????????? Scope for computecirc function

5 Function Scope Each function is assigned a data area in the memory. The variables defined inside one function are accessible only in that function* Does that mean we need to ask the user for the radius of circle twice? Int main() { double area, circ; area = computearea(); circ = computecirc(); printf( area is: %f\n, area); printf( circ is: %f\n, circ); return 0; } *That is if we use the name of the variable to access it and not the address. More on this, later.

6 Functions with input Arguments Luckily C allows us to give input to functions Int main() { double rad = 0.0, area = 0.0, circ = 0.0; printf( enter radius: ); scanf( %lf, &rad); area = computearea(rad); circ = computecirc(rad); } printf( area is: %f\n, area); printf( circ is: %f\n, circ); return 0;

7 Functions with input Arguments - Syntax Function header syntax: return_data_type function_name(arg1_data_type arg1, arg2_data_type arg2, ); Function implementation goes below the main function. return_data_type function_name(function_name(arg1_data_type arg1, arg2_data_type arg2, ) { /* write the implementation of function here */ } Example: double computeaverage(int x1, int x2);

8 int main() { Function with Arguments Memory View double radius = 0.0, area = 0.0; printf( Enter radius: ); scanf( %lf, radius); The memory for compute_area is allocated only when it is called, and it will be deallocated as soon as it returns! } area = computearea(radius); printf( area is: %f\n, area); return 0; double computearea(double rad) Name: Address: 1 Scope for main function area 2 radius area 8 rad 9 10 Content:?????????? { } double area; area = 2 * PI * rad; return area; Scope for computearea function

9 Functions with Arguments Order matters int main() double volumecone(double rad, double height) { { double radius = 0.0, height = 0.0, vol = 0.0; double volume = 0.0; printf( Enter radius and height: ); area = 2 * PI * rad; scanf( %lf%lf, radius, height); return volume; } vol = computearea(radius, height); } printf( area is: %f\n, area); return 0; Name: Address: 1 height 2 radius 3 vol volume 8 Content:?????????? rad 9 height 10 Scope for main function Scope for volumecone function

10 Functions Functions arguments must match with its caller in 3 ways: The order of arguments Number of arguments being passed Type of the data being passed The memory for compute_area is allocated only when it is called, and it will be deallocated as soon as it returns! Other functions are compiled after main() Place the function headers above the main

11 Global Variables Variables defined inside a function are local to that function and available only to that You can define variables above the main() and after the preprocessor directives (#); these variables will be available to all functions in the program. Variables defined in this way are global variables! Try avoiding global variables

12 More About Functions Functions can be identified by the parenthesis in front of them. (mostly) Can you remember any functions that we used without noticing that they were functions?

13 More About Functions Functions can be identified by the parenthesis in front of them. (mostly) Can you remember any functions that we used without noticing that they were functions? main(), printf(), scanf(), sqrt() are examples of functions. That s why we used #include These are predefined functions included in libraries

14 Examples of Library Functions stdlib.h: math.h: abs(int) ceil(double) floor(double) sin(double) cos(double) log(double) log10(double) pow(double, double)

15 Creating your own libraries: To create a library of your own: You will need to create a (.h) file and (.c) file for each library.h file for the library: Make a header file (.h) and give it a name representing the type of task it should do. Include all libraries you will need in your functions in the header file. Define all constant macros you will need in your functions in the header file Add all function headers to the header file..c file for the library Make a source file (.c) with the same name as the header. #include the header file you created in this source file. Implement the functions themselves in this source file. Now whenever you are writing a program that needs the functions you wrote before, just #include the header file you created.

16 Programming time Write a function roundmycustom() that computes the nearest integer of an input value. (for fractional part of smaller than 0.5 returns the integer part, for 0.5 and greater than that returns the integer part + 1.

17 Programming time Write a function roundmycustom() that computes the nearest integer of an input value. (for fractional part of smaller than 0.5 returns the integer part, for 0.5 and greater than that returns the integer part + 1. Compare this function with the function round() that is in math.h Modify your function to simulate the round() function.

18 Programming time Write a function roundmycustom() that computes the nearest integer of an input value. (for fractional part of smaller than 0.5 returns the integer part, for 0.5 and greater than that returns the integer part + 1. Compare this function with the function round() that is in math.h Modify your function to simulate the round() function. Can you write a similar function that input a dollar amount with arbitrary fractional part, returns the rounded amount in form of complete dollars and cents (dd.cc)?

19 Programming time Write a function roundmycustom() that computes the nearest integer of an input value. (for fractional part of smaller than 0.5 returns the integer part, for 0.5 and greater than that returns the integer part + 1. Compare this function with the function round() that is in math.h Modify your function to simulate the round() function. (from problems in your textbook) Write a program that takes a positive number with a fractional part and rounds it to two decimal places. For example, would round to (This can be used for rounding monetary values).

20 More Programming Problem 1 from chapter 3 of textbook

21 References J.R. Hanly & E.B. Koffman, Problem Solving and Program Design in C (8thed.), Pearson, 2016 Andy O Fallon s lecture notes for CptS121 (

Repetition Structures II

Lecture 9 Repetition Structures II For and do-while loops CptS 121 Summer 2016 Armen Abnousi Types of Control Structures Sequential All programs that we have written so far The statements inside a pair