Lecture3

1. Lecture3

2. Lecture Outline • Program Layout • Executable Statements • Input/Output Statements • Input/Output Operation • scanf function • printf function • Assignment Statements • Arithmetic Operations • The Return Statement • Comments in Programs • A Complete C Program • Mixed Data Types in Assignment Statements • Expressions with multiple operators • Rules for Expression Evaluation • Writing mathematical Formulas in C • Types of Errors

3. Program Layout Preprocessor Directive int main(void) { Declaration Executable Statements } • A C program line beginning with # that provides an instruction to the preprocessor. Examples: #include, #define. • Function main indicates the start of the program. • The part of a program that tells the compiler the names of memory cells and their data types. • Program commands that are converted to machine code by the compiler.

4. Input/Output Statements (functions) • Getting information in and out of a program. Assignment Statements • Doing calculations. Executable Statements

5. Input Operation • An instruction that copies data from an input device into memory. Output Operation • An instruction that displays information stored in memory. Input/Output Operations

6. Input Functions • Perform input operations. • Example: scanf. Output Functions • Perform output operations. • Example: printf. Input/Output Functions

7. Syntax scanf(format string, input list); Example scanf("%c%i", &firstinitial, &age); H32 placeholder scanf • The scanf function gets data entered by the user and copies it into memory.

8. Placeholder Variable Type Function Use %c char printf/scanf %i or %d int printf/scanf %f float printf/scanf Placeholder • A placeholder is a symbol beginning with % in a format string that indicates where to display the output value.

9. Examples scanf("%i",&workhours); scanf("%c",&letter); scanf("%i",&student_ID); scanf("%f",&tot_score); scanf("%f",&temperature); scanf("%f",&working_hours); scanf("%i%c",&population,&firstinitial);

10. Syntax printf(format string); printf(format string, print list); Note: a format string is always enclosed in " " placeholder newline escape sequence Example printf("That equals %fKilometers.\n",kms); function name format string print list printf • The printf function displays information on the screen.

11. New Line Escape Sequence "\n" • Is the newline escape sequence symbol which is placed in a printf to skip to a new line.

12. Examples printf("Please enter the student's grades:"); Please enter the student's grades: printf("The class average is %f",average); The class average is95.5. printf("The total area is %f and the total cost is %i S.R.",tarea,tcost); The total area is60.2and the total cost is4530S.R. printf("The student received an %c grade in the course.",grade); The student received anAgrade in the course.

13. Examples (Continue) printf("The grade is %c%c", grade,gradesymb); The grade isA+ printf("I am the first line\n"); printf("\nI am the second line\n"); I am the first line I am the second line

14. 234 %4i 234 234 %5i 234 -234 %5i -234 Formatting Numbers in Program Output Value Format Displayed Output 234 %1i 234 -234 %4i -234 -234 %2i -234

15. .123 %6.2f 0.12 -9.536 %6.2f -9.54 Formatting Numbers in Program Output Value Format Displayed Output -99.42 %6.2f -99.42 -25.554 %6.2f -25.55 99.999 %6.2f 100.00 999.4 %6.2f 999.40

16. 3.14159 %5.2f 3.14 Formatting Numbers in Program Output Value Format Displayed Output 3.14159 %3.2f 3.14 .1234 %4.2f 0.12 -.006 %.3f -0.006 -.006 %4.2f -0.01 -3.14159 %.4f -3.1416

17. Syntax Variable=expression; Examples Total_Grades = Grade1 + Grade2 + Grade3; No_Students = 3; Average = Total_Grades / No_Students; Assignment Statements • It stores a value or a computational result in a variable. • It is used to perform most arithmetic operations in a program.

18. Arithmetic Expressions Arithmetic Meaning Operator + addition - subtraction * multiplication / division % remainder

19. Examples 5 % 3 = 2 5 % 4 = 1 15 % 5 = 0 15 % 6 = 3 7 % 5 = 2 8 % 5 =3 3 % 5 = 3 4 % 5 = 4 5 % 5 = 0 6 % 5 = 1 7 % 5 = 2 8 % 5 =3 The % Operation (Remainder)

20. C Language Elements #include <stdio.h> #define KMS_PER_MILE 1.609 int main(void) { float miles, kms; printf("Enter the distance in miles: "); scanf("%f", &miles); kms = KMS_PER_MILE * miles; printf("That equals %.2f kilometers.\n", kms); return(0); }

21. Syntax return expression; Example return(0); The Return statement • The return statement transfers control from a function back to the activator of the function. • For function main, control is transferred back to the operating system • The value of expression is returned as the result of the function execution.

22. Syntax /* comment text*/ Examples /* This is a one line comment */ /* * This is a multiple line comment in which the stars not immediately * proceeded or followed by slashes have no special syntactic * significance */ Comments in programs

23. A Complete C Program /* converts distances from miles to kilometers */ #include <stdio.h> /* printf, scanf definitions */ #define KMS_PER_MILE 1.609 /* conversion constant */ int main(void) { float miles, /* distance in miles */ kms; /* equivalent distance in kilometers */ /* get the distance in miles */ printf("Enter the distance in miles: "); scanf("%f", &miles); /* convert the distance to kilometers */ kms = KMS_PER_MILE * miles; /* display the distance in kilometers */ printf("That equals %.2f kilometers.\n", kms); return(0); }

24. 3 3.50 20 20.00 Mixed Data Types in an Assignment Statement • The variable to the left of the equals sign determines the data types of an expression. • Example: if x is int and y is float then x = 7 * 0.5; y = 7 * 0.5; x = 100/5; y = 100/5;

25. Unary operators: • Take only one operand. • Example: x = -y; p = +x * y • Binary operators: • Requires two operands. • Example: x = y + 2; Expressions with multiple operators • Operators with multiple operators are common in C. • Example: x = b * b - 4 * a * c • These expressions can include:

26. Rule # 1: Parentheses rule • All expressions in parentheses must be evaluated separately. • Nested parenthesized expressions must be evaluated from the inside out. • Example: ( ( a + b ) / ( c + d ) ) * 2 Rules for Expression Evaluation

27. Rule # 2: Operator precedence rule • Operators in the same expression are evaluated in the following order: unary + , - first * , / , % next binary + , - last • Example: a + b * c Rules for Expression Evaluation

28. Rule # 3: Associativity rule • Right associativity: unary operator in the same sub-expression and at the same level (such as + and -) are evaluated right to left. • Left associativity: Binary operator in the same sub-expression and at the same level (such as + and -) are evaluated left to right. • Example: a + b - c Rules for Expression Evaluation

29. Rules for Expression Evaluation (Examples) z - ( a + b / 2 ) + w * - y ( b * b ) - ( 4 * 4 ) * ( a * c ) A * - ( b + c )

30. Use parentheses when required to control the order of operator evaluation. Example: a + b = ( a + b ) / ( c + d ) c + d Writing Mathematical Formulas in C • Always specify multiplication explicitly by using the operator * where needed. Example: b² - 4 a c = b * b - 4 * a * c • Two arithmetic operators can be written in succession if the second is a unary operator Example: a x - ( b + c ) = a * - ( b + c )

31. 1 1 + a² Writing Mathematical Formulas in C (Examples) Examples: a + b - c = a + b - c = 1 / ( 1 + a * a) a x (5b + c) = a * ( 5 * b + c )

32. Types of Errors • Syntax error: a violation of the C grammar rules. Detected during compilation. • Logic error: an error caused by following an incorrect algorithm. • Run-time Error: an attempt to perform an invalid operation, detected during program execution. Example: dividing a number by zero.