BIL104E: Introduction to Scientific and Engineering Computing, Spring 2005. Lecture 2 Outline 2.1 Introduction 2.2 Basics of C Programs Constants and Variables Expressions Statements and Statement blocks C function types and names Arguments to functions The body of a function and Function calls 2.3 Another Simple C Program: Adding Two Integers 2.4 Memory Concepts 2.5 Data Types int float char 2.6 Arithmetic in C 2.7 Keywords in C

2.2 The Basics of the C Program Before we go into detail of C programming Language Syntax let us look at the basic definitions: Constants and variables Expressions Statements Statement blocks C function types and names Arguments to functions The body of a function Function calls

The Basics of the C Program As a building is made of bricks, a C program is made of basic elements, such as expressions, statements, statement blocks, and function blocks. But first, you need to learn two smaller but important elements, constant and variable, which make up expressions. Constants and Variables : As its name implies, a constant is a value that never changes. A variable, on the other hand, can be used to present different values. Expressions An expression is a combination of constants, variables, and operators that are used to denote computations. For instance, the following: (2 + 3) * 10 is an expression that adds 2 and 3 first, and then multiplies the result of the addition by 10. (The final result of the expression is 50.) Similarly, the expression 10 * (4 + 5) yields 90. The 80/4 expression results in 20.

The Basics of the C Program Expression Description 6  An expression of a constant. i  An expression of a variable. 6 + i  An expression of a constant plus a variable. Exit(0)  An expression of a function call. Arithmetic Operators As you've seen, an expression can contain symbols such as +, *, and /. In the C language, these symbols are called arithmetic operators. Symbol Meaning + Addition - Subtraction * Multiplication / Division % Remainder (or modulus)

The Basics of the C Program Among the arithmetic operators, the multiplication, division, and remainder operators have a higher precedence than the addition and subtraction operators. For example, the expression 2 + 3 * 10 yields 32, not 50. Because of the higher precedence of the multiplication operator, 3 * 10 is calculated first, and then 2 is added into the result of the multiplication. As you might know, you can put parentheses around an addition (or subtraction) to force the addition (or subtraction) to be performed before a multiplication, division, or modulus computation. For instance, the expression (2 + 3) * 10 performs the addition of 2 and 3 first before it does the multiplication of 10.

The Basics of the C Program Statements In the C language, a statement is a complete instruction, ending with a semicolon. In many cases, you can turn an expression into a statement by simply adding a semicolon at the end of the expression. For instance, the following i = 1; is a statement. You may have already figured out that the statement consists of an expression of i = 1 and a semicolon (;). Here are some other examples of statements: i = (2 + 3) * 10; i = 2 + 3 * 10; j = 6 % 4; k = i + j; Also, below are C statements. return 0; exit(0); printf ("Howdy, neighbor! This is my first C program.\n");

The Basics of the C Program Statement Blocks A group of statements can form a statement block that starts with an opening brace ({) and ends with a closing brace (}). A statement block is treated as a single statement by the C compiler. For instance, the following for(. . .) { s3 = s1 + s2; mul = s3 * c; remainder = sum % c; } is a statement block that starts with { and ends with } Anatomy of a C Function Functions are the building blocks of C programs. Besides the standard C library functions, you can also use some other functions made by you or another programmer in your C program. In Hour 2 you saw the main() function, as well as two C library functions, printf() and exit(). Now, let's have a closer look at functions.

Function’s Anatomy

The Basics of the C Program Giving a Function a Valid Name A function name is given in such a way that it reflects what the function can do. For instance, the name of the printf() function means "print formatted data." There are certain rules you have to follow to make a valid function name. The following are examples of illegal function names in C: Illegal Name The Rule 2 (digit) A function name cannot start with a digit. * (Asterisk) A function name cannot start with an asterisk. + (Addition) A function name cannot start with one of the arithmetic signs that are reserved C keywords. . (dot) A function name cannot start with .. total-number A function name cannot contain a minus sign. account'97 A function name cannot contain an apostrophe.

The Basics of the C Program Arguments to C Functions You often need to pass a function some information before executing it. For example, in first program, “Hello World.\n", is passed to the printf() function, and then printf() prints the string on the screen. Pieces of information passed to functions are known as arguments. The argument of a function is placed between the parentheses that immediately follow the function name. The number of arguments to a function is determined by the task of the function. If a function needs more than one argument, arguments passed to the function must be separated by commas; these arguments are considered an argument list. If no information needs to be passed to a function, you just leave the argument field between the parentheses blank. The Beginning and End of a Function As you may have already figured out, braces are used to mark the beginning and end of a function. The opening brace ({) signifies the start of a function body, while the closing brace (}) marks the end of the function body. As mentioned earlier, the braces are also used to mark the beginning and end of a statement block. You can think of it as a natural extension to use braces with functions because a function body can contain several statements.

The Basics of the C Program The Function Body The function body in a function is the place that contains variable declarations and C statements. The task of a function is accomplished by executing the statements inside the function body one at a time. Listing below demonstrates a function that adds two integers specified by its argument and returns the result of the addition. Listing: A function that adds two integers. /* This function adds two integers and returns the result */ int integer_add( int x, int y ) { int result; result = x + y; return result; }

The Basics of the C Program #include <stdio.h> /* This function adds two integers and returns the result */ int integer_add( int x, int y ){ int result; result = x + y; return result; } int main(){ int sum; sum = integer_add( 5, 12); /* Function Call */ printf("The addition of 5 and 12 is %d\n", sum); return 0;

The Basics of the C Program Summary In this lesson you've learned the following: A constant in C is a value that never changes. A variable, on the other hand, can present different values. A combination of constants, variables, and operators is called an expression in the C language. An expression is used to denote different computations. The arithmetic operators include +, -, *, /, and %. A statement consists of a complete expression suffixed with a semicolon. The C compiler treats a statement block as a single statement, although the statement block may contain more than one statement. The function type of a function determines the type of the return value made by the function. You have to follow certain rules to make a valid function name. An argument contains information that you want to pass to a function. An argument list contains two or more arguments that are separated by commas. The opening brace ({) and closing brace (}) are used to mark the start and end of a C function. A function body contains variable declarations and statements. Usually, a function should accomplish just one task.

2.3 Another Simple C Program: Adding Two Integers 1. Initialize variables 2. Input 2.1 Sum 3. Print Program Output 1 2 /* Addition program */ 3 #include <stdio.h> 4 5 int main() 6 { 7 int integer1, integer2, sum; /* declaration */ 8 9 printf( "Enter first integer\n" ); /* prompt */ 10 scanf( "%d", &integer1 ); /* read an integer */ 11 printf( "Enter second integer\n" ); /* prompt */ 12 scanf( "%d", &integer2 ); /* read an integer */ 13 sum = integer1 + integer2; /* assignment of sum */ 14 printf( "Sum is %d\n", sum ); /* print sum */ 15 16 return 0; /* indicate that program ended successfully */ 17 } Enter first integer 45 Enter second integer 72 Sum is 117

2.3 Another Simple C Program: Adding Two Integers As before Comments, #include <stdio.h> and main int integer1, integer2, sum; Declaration of variables Variables: locations in memory where a value can be stored int means the variables can hold integers (-1, 3, 0, 47) Variable names (identifiers) integer1, integer2, sum Identifiers: consist of letters, digits (cannot begin with a digit) and underscores( _ ) Case sensitive Declarations appear before executable statements If an executable statement references and undeclared variable it will produce a syntax (compiler) error

2.3 Another Simple C Program: Adding Two Integers scanf( "%d", &integer1 ); Obtains a value from the user scanf uses standard input (usually keyboard) This scanf statement has two arguments %d - indicates data should be a decimal integer &integer1 - location in memory to store variable & is confusing in beginning – for now, just remember to include it with the variable name in scanf statements When executing the program the user responds to the scanf statement by typing in a number, then pressing the enter (return) key

2.3 Another Simple C Program: Adding Two Integers = (assignment operator) Assigns a value to a variable Is a binary operator (has two operands) sum = variable1 + variable2; sum gets variable1 + variable2; Variable receiving value on left printf( "Sum is %d\n", sum ); Similar to scanf %d means decimal integer will be printed sum specifies what integer will be printed Calculations can be performed inside printf statements printf( "Sum is %d\n", integer1 + integer2 );

A visual representation 2.4 Memory Concepts Variables Variable names correspond to locations in the computer's memory Every variable has a name, a type, a size and a value Whenever a new value is placed into a variable (through scanf, for example), it replaces (and destroys) the previous value Reading variables from memory does not change them A visual representation integer1 45

2.5 Data Types : char The char Data Type An object of the char data type represents a single character of the character set used by your computer. For example, A is a character, and so is a. But 7 is a number. But a computer can only store numeric code. Therefore, characters such as A, a, B, b, and so on all have a unique numeric code that is used by computers to represent the characters. Usually, a character takes 8 bits (that is, 1 byte) to store its numeric code. For many computers, the ASCII (American Standard Code for Information Interchange) codes are the de facto standard codes to represent a character set. The original ASCII character set has only 128 characters because it uses the lower 7 bits that can represent 27 (that is, 128) characters. On IBM-compatible PCs, however, the character set is extended to contain a total of 256 (that is, 28) characters. Appendix C, "ASCII Character Set," gives a list of the 256 characters.

2.5 Data Types : char Character Constants The Escape Character (\) A character enclosed in single quotes (`) is called a character constant. For instance, `A', `a', `B', and `b' are all character constants that have their unique numeric values in the ASCII character set. Given x as a character variable, for instance, the following two assignment statements are equivalent: x = `A'; x = 65; So are the following two statements: x = `a'; x = 97; The Escape Character (\) In the C language, the backslash (\) is called the escape character; it tells the computer that a special character follows. For instance, when the computer sees \ in the newline character \n, it knows that the next character, n, causes a sequence of a carriage return and a line feed. Besides the newline character, several other special characters exist in the C language, such as the following: Character Description \b The backspace character; moves the cursor to the left one character. \f The form-feed character; goes to the top of a new page. \r The return character; returns to the beginning of the current line. \t The tab character; advances to the next tab stop.

2.5 Data Types : int The int Data Type You saw the integer data type in Hour 3. The int keyword is used to specify the type of a variable as an integer. Integer numbers are also called whole numbers, which have no fractional part or decimal point. Therefore, the result of an integer division is truncated, simply because any fraction part is ignored. Depending on the operating system and the C compiler you're using, the length of an integer varies. On most UNIX workstations, for example, an integer is 32 bits long, which means that the range of an integer is from 2147483647 (that is, 231_1) to -2147483648. The range of a 16-bit integer is from 32767 (that is, 215_1) to -32768. Declaring Integer Variables You also saw the declaration of an integer in Hour 3. The following shows the basic declaration format: int variablename; Similar to the character declaration, if you have more than one variable to declare, you can use either the format like this int variablename1; int variablename2; int variablename3; or like this: int variablename1, variablename2, variablename3;

2.5 Data Types : float The float Data Type The floating-point number is another data type in the C language. Unlike an integer number, a floating-point number contains a decimal point. For instance, 7.01 is a floating-point number; so are 5.71 and -3.14. A floating-point number is also called a real number. A floating-point number is specified by the float keyword in the C language. Like an integer number, a floating-point number has a limited range. The ANSI standard requires that the range be at least plus or minus 1.0*1037. Normally, a floating-point number is represented by taking 32 bits. Therefore, a floating-point number in C is of at least six digits of precision. That is, for a floating-point number, there are at least six digits (or decimal places) on the right side of the decimal point. Not like an integer division from which the result is truncated and the fraction part is discarded, a floating-point division produces another floating-point number. A floating-point division is carried out if both the divisor and the dividend, or one of them, are floating-point numbers. For instance, 571.2 / 10.0 produces another floating-point number, 57.12. So do 571.2 / 10 and 5712 / 10.0. Declaring Floating-Point Variables The following shows the declaration format for a floating-point variable: float variablename; float variablename1; float variablename2; float variablename3; or like the following one: float variablename1, variablename2, variablename3;

2.5 Data Types: Summary Data Type C keyword Format specifier İnteger int %d or %i Charachter char %c Floating (real) float %f Double (long float) double %lf For engineering notation use %e or %E For hexadecimal representation use %x or %X For octal representation use %o or %O

2.5 Data Types : Summary contiunes / (division operator) has special meaning in such: 4/5 = 0 (int/int)  pay attention to this 4/5.0 = 0.8 (int/float) 4.0/5 = 0.8 (float/int) 4.0/5.0 = 0.8 (float/float) Type CASTING (float) 4/5  0.8 (int) 3/6  0

Arithmetic calculations Use * for multiplication and / for division Integer division truncates remainder 7 / 5 evaluates to 1 Modulus operator(%) returns the remainder 7 % 5 evaluates to 2 Operator precedence Some arithmetic operators act before others (i.e., multiplication before addition) Use parenthesis when needed Example: Find the average of three variables a, b and c Do not use: a + b + c / 3 Use: (a + b + c ) / 3

2.5 Arithmetic Arithmetic operators: Rules of operator precedence:

2.6 Keywords in C Keywords in C Special words reserved for C Cannot be used as identifiers or variable names