KK10103 – Computer Programming

KK10103 – Computer Programming Chapter 2 : Overview of C By Suraya Alias

2.0 The Hello World Program /*The classic HelloWorld */ #include <stdio.h> int main(void) { printf(“Hello World!!"); return 0; }

2.1 C Language Element • /*The classic HelloWorld */ • These are comments, starts with /* ends with */, // is used to comment out per line. • #include <stdio.h> • Lines begin with # is the preprocessing directives which communicates with the processor. • #include <stdio.h> means to include standard header file that has definitions such as printf and scanf. • The other preprocessor directive is #define, such as #define HOUR 60 , which means that the constant macro HOUR has the value of 60. • Syntax : #define NAME value

2.1 C Language Element • int main (void) • The main function is where the execution begins. • The braces { } enclose the main function body, which contains declaration and executable statements. • The keyword int indicates that the main function returns an integer value 0 after the execution ends. • The keyword void means the main function takes no argument • The function body has two parts : declaration and executable statements. • Every declarations and statements ends with semicolon ; in C programming

2.1 C Language Element • Reserved words • a word that has special meaning in C • Such as int, void, double and return • Standard Identifiers • also has special meaning such as printf and scanf • User Defined Identifiers • user can define their own identifiers such as HOUR, KM_PER_MILE • An identifier must consist only letters, digit and underscore • An identifier cannot begin with a digit • A C reserved word cannot be used as an identifier • Lowercase and uppercase identifiers does make a different in C. The names Rate and rate and RATE is considered as different identifiers.

2.2 Variable Declaration and Data Types • Variables • a memory cell used to store value and can be changed as the programs executes • Variable Declaration • statement that tells the compiler the variable name and the value stored in the variable. • The Variable declarations starts with an identifier followed by the variable name such as : int count; double x, y, x; char w; • Data types • a set of values and operations that can be performed on those values • Data type int – to represent integers in C, such as 77 • Data type double – a real number that is separated by decimal point, such as 1.5674 and 0.09 • Data type char – represents an individual character value such as a letter, digit or special symbol. Such as ‘A’, ‘7’, ‘:’

Figure 2.1 C Language Elements in Miles-to-Kilometers Conversion Program

Figure 2.2 Memory(a) Before and (b) After Execution of a Program 2.3 Executable Statements

Figure 2.3 Effect of kms = KMS_PER_MILE * miles;

Figure 2.4 Effect of sum = sum + item;

Input / Output Operations • The printf function • Used for printing formatted output and prompting message • printf(“Please enter a number>”) • printf(“That equals %f kilometers.\n ”, kms); • That equals 16.090000 kilometers • %f is the placeholder which is replaced by the value from kms • A placeholder always begins with the symbol % • The scanf function • Used to read formatted input • scanf(“%lf”, &miles); • The format “%lf” is the placeholder that tells scanf what kind of data to copy to variable miles • The name of each variable is preceded by & character

Figure 2.5 Effect of scanf("%lf", &miles);

Placeholder in Format Strings • Multiple placeholder • printf (“Hi %c%c%c – you will be %d years old today \n”, letter_1, letter_2, letter_3, age); • Will display as • Hi BOB – you will be 32 years old today

Figure 2.6 Scanning Data Line Bob

Figure 2.7 General Form of a C Program

2.5 Arithmetic Expression • Rules for evaluating Expression • Parentheses rules • Solve or evaluate expression in bracket first • Operator Precedence Rules • Unary + - • * / % • Binary + - • Associativity Rules • For same level, left to right

Figure 2.8 Evaluation Tree for area = PI * radius * radius;

Figure 2.9 Step-by-Step Expression Evaluation

Figure 2.10 Evaluation Tree and Evaluation forv = (p2 - p1) / (t2 - t1);

Figure 2.11 Evaluation Tree and Evaluation for z - (a + b / 2) + w * -y

Figure 2.12 Supermarket Coin Value Program

Figure 2.12 Supermarket Coin Value Program (cont’d)

Figure 2.13 Batch Version of Miles-to-Kilometers Conversion Program

2.6 Formatting Numbers in Program Output • Formatting values of Type int • By using field width • printf(“Results: %3d meters = %4d ft. %2d in. \n”, meters, feet, inches); • Results : 21 meters= 68 ft. 11 in. • Formatting values of Type double • To display the value of x to an accuracy of 2 decimal place we can use the placeholder %6.2f • Example : x is -25.554 will be displayed as -25.55

2.7 Interactive Mode, Batch Mode and Data Files • Interactive mode • A mode where user responds to prompt by entering data • Batch mode • Programs scans data from data file

Figure 2.13Batch Version of Miles-to-Kilometers Conversion Program

Program controlled Input and output files Using the FILE * command FILE *inp, /* pointer to input file */ *outp; /* pointer to output file */ /* Open the input and output files. */ inp = fopen("D:\\distance.txt", "r"); outp = fopen("D:\\distanceout.txt", "w"); /* Get and echo the distance in miles. */ fscanf(inp, "%lf", &miles); fprintf(outp, "The distance in miles is %.2f.\n", miles); /* Display the distance in kilometers. */ fprintf(outp, "That equals %.2f kilometers.\n", kms); /* Close files. */ fclose(inp); fclose(outp);

Figure 2.14 Miles-to-Kilometers Conversion Program with Named Files

Figure 2.15 Compiler Listing of a Program with Syntax Errors

Figure 2.16 A Program with a Run-Time Error

Figure 2.17 Revised Start of main Function for Supermarket Coin Value Program

Figure 2.18 A Program That Produces Incorrect Results Due to & Omission

KK10103 – Computer Programming