The First C Program

1. /* This program prints Hello World! to screen */ #include <stdio.h> int main() { printf(“Hello World!\n”); return 0; } The First C Program Comments are ignored by the compiler Preprocessor directive stdio.h is the header file containing I/O function declarations Each C program must have one main function Prints Hello World! and ‘\n’ advances the cursor to a newline Each C statement ends with a ‘;’ Problem Solving Using C

2. A Sequence Structure Example • Write a program to calculate the tax paid by an employee • Pseudocode: • print “A program that computes income tax” • print “Enter gross income:” • read gross_income • tax = 0.0175 gross_income • print “Tax is ” tax “dollars.” Problem Solving Using C

3. A Sequence Structure Example /********************************************************** Author : Uckan Purpose : Computes tax as 1.75% of gross income. Input from : Terminal keyboard Output to : Screen **********************************************************/ #include <stdio.h> const double TAX_RATE = 0.0175; int main(void) { /* Variable declarations: */ double gross_income; double tax; /* Function body: */ printf("A PROGRAM THAT COMPUTES INCOME TAX\n"); printf("Enter gross income: "); scanf("%lf", &gross_income); tax = TAX_RATE * gross_income; printf(“Tax is %lf dollars.", tax); return 0; } Problem Solving Using C

4. Dissection of the Program • printf(): Function for printing text, values, etc. • scanf(): Function for reading a value. It will wait for the user to enter a value • tax = TAX_RATE * gross_income; • * Multiplication operator • = Assignment operator • We will explain the purpose of %lf in printf() and scanf() a little later! Problem Solving Using C

5. C has 6 Kinds of Tokens of Language Elements • Reserved words: const, double, int, return, if, while, … • Identifiers: Programmer defined words for variables and functions. Identifiers must be unique • Constants: Fixed values • String literals: Sequence of characters • Punctuators: [ ] ( ) { } , ; : … * # • Operators: Tokens that result in some kind of operation. Operators act on operands • Unary operators: Require one operand: e.g. Minus: -15 • Binary operators: Require two operands: e.g. Multiplication: 25*4 Problem Solving Using C

6. Rules for Constructing Identifiers • Identifiers can consist of capital letters, lower case letters, digits, and underscore character ‘_’ • Valid: myVariable, my_variable, _tax, income4 • Invalid: myVariable+yourVariable, oh!no • First character must be a letter or an underscore • Invalid: 2grade • In general, there is no length limitation • No embedded blanks are allowed • Invalid: my grade • Reserved words cannot be used as identifiers • Identifiers are case sensitive • MYGRADE and mygrade are different in C! Problem Solving Using C

7. Data Types and Declarations • Declaration: Associating a type with a program entity such as a variable. • Data type: A set of data values and a set of operations on those values. • Named constants • const double TAX_RATE=0.0175; • Value of TAX_RATE does not change throughout the program • C has two classes of data types • Built-in (we’ll learn these in CMPE 101) • Programmer defined (see those in CMPE 102) Problem Solving Using C

8. Fundamental Data Types in C • int: Integer: e.g. 1244, -87 • If 2 bytes are used to store integers, range of integers is from -215 to 215-1 (or -32,768 to 32,767) (Q: What does 1st bit do?) • char: Character: ‘a’, ‘A’, ‘4’ • double: Floating-point: 0.5678, -3.25, 2.0e4, 2.3e-1 • The scientific notation: 2.0e4=2.0104,2.3e-1=2.3 10-1) • float: Floating-point (less precision) • 8 is an integer, 8.0 is a double, 8.0F is a float • void: “Nothing” Note that some of these data types are preceded by short, long, signed, and unsigned: e.g. short int Problem Solving Using C

9. Derived Data Types • Strings: A sequence of characters • e.g.: “This is a string” • Note double quotation marks “ ” • “a” is a string, ‘a’ is a character • String variables are declared as follows: char student_name[31]; • The string length must not exceed 30 characters since the string must be terminated by the null character ‘\0’ Problem Solving Using C

10. Input of String Variables • We use the function gets(StringVariable): Get string • Program segment: char student_name[31]; gets(student_name); • gets() waits for the user to enter a string. The string’s length must not exceed the string variable’s declared length (in this case 30) Problem Solving Using C

11. C Statements • A statement is a specification of an action to be taken as the program executes • Each C statement ends with a semi-colon ; • A compound statement is a list of statements enclosed in curly braces { } • Some types of statements: • Expressions, selections, repetitions, etc. Problem Solving Using C

12. Data Initialization • char ch; • Just a declaration for the variable ch • char ch=‘a’; • Compile-time initialization of variable ch • ch=‘a’; • Run-time initialization of variable ch Problem Solving Using C

13. Assignments and Expressions • Expression: Syntactically correct and meaningful combination of operators and operands: • TAX_RATE * gross_income • Assignment operator: = • tax = TAX_RATE * gross_income; • tax and TAX_RATE * gross_income are operands • TAX_RATE * gross_income is also an expression • Variable = Arithmetic Expression • Computes the value for the expression and stores the result in memory cell for the variable • Q: How does the memory cell containing the value of current year change as the following statements are executed? int current_year = 2005; current_year = 2006; Problem Solving Using C

14. Standard Output Function • printf() • printf() is in fact a call to a standard library function • We’ll look at function calls in detail later • To useit,you will need to include stdio.h header file by typing #include <stdio.h> at the beginning of program • There are two syntactical forms of printf(): • printf(FormatControlString); • e.g. printf(“Hello\n”); • printf(FormatControlString, PrintList); • e.g. int year=2006; printf(“Year is %d”, year); Problem Solving Using C

15. Format Specifiers for printf() • int: %d • float: %f • double: %lf • char: %c • string: %s double height=1.80; int year=2006; printf(“My height is %lf in year %d.\n”, height, year); Problem Solving Using C

16. Standard Input Function • scanf() • scanf() is in fact a call to a standard library function • It is used for interactive input • To useit,you will need to include stdio.h header file by typing #include <stdio.h> at the beginning of program • Syntactical forms of scanf(): • scanf(FormatControlString, InputList); • e.g. int age; printf(“%d”, &age); • FormatControlString must consist of format specifiers only Problem Solving Using C

17. More on scanf() • Each element in InputList in scanf() call must be an address to a memory location • If the element is not an address, it must be made into an address by prefixing the variable name by an ampersand character & • & is called the address operator in C int age; scanf(“%d”, &age); Problem Solving Using C

18. Format Specifiers for scanf() • int: %d • float: %f • double: %lf • char: %c double height; int year; scanf(“%lf”, &height); scanf(“%d”, &year); scanf(“%lf”, height); /* This is an error!! */ Problem Solving Using C

19. A Conversion Program in C /************************************************************* Purpose: Converts height from inches to centimeters, and weight from pounds to kilograms *************************************************************/ #include <stdio.h> int main(void) { /* Variable declarations: */ int height_in_inches, weight_in_pounds; double height_in_centimeters, weight_in_kilograms; /* Function body: */ printf("Enter your height in \"inches\": "); scanf("%d", &height_in_inches); height_in_centimeters = 2.54 * height_in_inches; printf("Enter your weight in \"pounds\": "); scanf("%d", &weight_in_pounds); weight_in_kilograms = 0.45359 * weight_in_pounds; printf("your height is %lf centimeters, ", height_in_centimeters); printf("\nand your weight is %lf kilograms.", weight_in_kilograms); return 0; } Problem Solving Using C