Loops functions in C and some examples, Lecture notes of C programming

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Lecture 4

Iterative Constructs

Functions

EEE 11

Preprocessor Directives

● Commands that give instructions to the C preprocessor

● A preprocessor is a program that takes text and performs

lexical conversions on it.

− Prepares data for the compiler/interpreter

● The conversions may include macro substitution, conditional

inclusion, and inclusion of other files.

● Preprocessor directives begins with a

− Two examples: #include directive #define directive

Preprocessor Directives

● #define directive

− Can be used for compile-time constants − Cannot be used for things that vary during program runtime. − Supports parameterized macros (more advanced usage)

Syntax: #define NAME expansion

Example: #define KMS_PER_MILE 1.

#define PI 3.

Programming Style: Constants

● Use the #define preprocessor for constants

● Poor code area = radius * radius * 3.14159; circumference = 2 * radius * 3.14159;

● Better code #define VAL_PI 3. ... area = radius * radius * VAL_PI; circumference = 2 * radius * VAL_PI;

− Makes code more readable − Easier to remember − Easier to maintain

Iterative/loop constructs

● Repetitions in program code

● Sample problems.

− Input handling ● Ask for another input if user gave an invalid input ● Prompt user if they want to give another input

− Repetitive tasks ● Compute pay for several employees (same formula) ● Counting number of inputs

Main components of a loop

● Loops involving a control variable:

− Initialization ● The controlling variable must be initially set to a known valid state. − Testing (the loop repetition condition) ● An expression involving the controlling variable must be evaluated to determine if the loop will continue or not. − Update ● The controlling variable must be updated in a way that the loop repetition condition will eventually terminate the loop

While syntax

● Standard while syntax:

initialization

while ( repetition condition ) {

loop body Update } − The loop repetition expression is evaluated to determine if the loop will execute the statement

i = 0; while (i <= 5) { i = i + 1; }

Sample 04-01 (while)

count_emp < 7

count_emp = 0

True

False Display “all employees processed”

END

Display pay

Input hours, rate

pay = hours*rate

count_emp = count_emp+

Sample 04-02 (for)

count_emp < 7

count_emp = 0

True

False Display “all employees processed”

END

Display pay

Input hours, rate

pay = hours*rate

count_emp = count_emp+

WHILE vs FOR loop

● while-loop

Initialization ;

while ( Test ) { body; Update ; }

● For-loop

for( Initialization ; Test ; Update ) { body; }

Multiple initializations

● Initialization and updates are not limited to one

/* Double counters */ int main (void) { int x; int y;

for ( x=0, y=0; x<1000 && y<2000; x+=1, y+=2) { printf("%d \t %d\n", x, y); } return (0); }

Analyzing loops

● Use tables

− Columns are variables/expressions/conditions − Rows are loop iteration

● What is the output?

Suggested columns: i, i<=5, 10-i

i = 0; while (i <= 5) { printf("%3d %3d\n", i, 10-i); i = i + 1; }

do-while statement

● Loops that must execute at least once are

implemented in C using a do-while statement.

● Both the for and while statements evaluate the

repetition condition BEFORE executing the

statement block.

do-while statement

● Standard Syntax:

initialization; do { Loop body update } while ( repetition condition );

● Loop body is executed at least once.

● Note the semicolon (;) at the end

do { printf("Enter the number 5: "); scanf("%d", &number); } while (number != 5);