A First Book of ANSI C, Fourth Edition1 Functions for Modularity 04/24/15.

A First Book of ANSI C, Fourth Edition 1

Functions for Modularity

04/24/15


Final Exam

Friday, May 8th, 12:30-2:30 Accumlative Emphasis on Loops and Functions, Chapters 5 &

6 You may bring a half sheet of notes to the exam.


Programs

Program 6 is graded. Program 9 is page 297, #4 a&b.

– Extra point for screen shot of evaluation proof.


Objectives

• Use Function and Parameter Declarations.

• Return a Value from a Function.


Functions

• Like small programs within the program.• Help to divide the program up to make it easier to

write and debug.– Modularity

• Make it easier to reuse code in new programs.• Example in half.c


Function Call Called function

A function that is called into action by its reference in another function.

Calling function A function that calls another function main() calls half() in half.c


Function Call May Pass Data


Book Example

• Data Passed is receive by a parameter.• A parameter otherwise acts like a variable in the

function.– void findMax(float x, float y)

• prog6.1.c


Function Definition

• Function header: data type of the return value, function name, and values expected by the function

• Function body: operates on the passed data and returns, at most, one value

• The variable names in the header line are known as parameters

• prog6.1.c


Function Definition


Function Parts

void findMax(float x, float y) //Header w/parameters{ //Body starts float maxnum;

if(x >= y) /* find the maximum number */ maxnum = x; else maxnum = y;

printf("\nThe maximum is %f\n", maxnum);}//Body ends


No Function Nesting

• main() is C function• Each C function is a separate and independent

entity with its own parameters and variables– Nested functions are not permitted


Placement of Statements

• All preprocessor directives, variables, named constants, and functions, except main(), must be either declared or defined before they can be used

• Basic (good) programming structure:preprocessor directivessymbolic constantsfunction prototypes can be placed hereint main(){ function prototypes can be placed here variable declarations; other executable statements; return value;}Function definitions


Write a Function

• Write a C function that accepts a number then outputs a message telling whether it is even or odd.

• Write a main program to input a number then use the function to tell whether it is even or odd.


Participation 1

Write a function mult() that takes two numbers and

prints out their product.


Returning a Value


Returning a Value

• Sometimes you want the function to find a value and send it back to the main program.

• Use the return statement to do that.


Returning a Value

• From its side of the return transaction, the called function must provide:– Data type of the returned value, which is specified in

the function’s header line– Actual value being returned, which is specified by a

return statement


Returning a Value (continue)


Returning a Value (continue)

• To return a value, use a return statement– return (expression); //or, return expression;

– The expression is evaluated first; – Its value is automatically converted to the return

value’s data type.• Unmatched types can cause unexpected results

– Returned to calling function.


Example

• ch6/height.c


Write a function

• Write a function that takes the base and height of a triangle and returns the area.

• Include the function in a working program.


Another Example

• Write a function that raises an integer to a positive integer power. It will return the result.


Participation 2

• Write a C function that takes two mile marker

readings and returns the distance between them.

• Write a main program to ask the user for two mile

marker values, then use the function to compute

the distance between and output it.


Functions with Empty Parameter Lists

• The prototype for a function with empty parameter list requires either writing the keyword void or nothing between the parentheses following the function’s name– int display(void);– int display();

• A function with an empty parameter list is called by its name with nothing written in the parentheses following the function’s name– display();


Example

• ch6/house.c

A First Book of ANSI C, Fourth Edition1 Functions for Modularity 04/24/15.

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