1. 1 CSE1301 Computer Programming Lecture 5: Components of a C Program (Part 1) Linda M c Iver

2. 2 Topics Structure of a C program Values and variables Expressions Function calls Comments

3. 3 From Algorithms to Programs Both are sets of instructions on how to do a task Algorithm: –talking to humans, easy to understand –in plain (English) language Program: –talking to computer (compiler) –can be regarded as a “formal expression” of an algorithm

4. 4 Basic Structure of a C Program output “Hello World!” Algorithm: #include int main() { printf(“Hello World!”); return 0; } C Program: Example: Hello World

5. 5 Basic Structure of a C Program (cont) #include int main() { printf(“Hello World!”); return 0; } C Program : Example: Hello world Includes standard input/output library of procedures. Read: “Hash-include”

6. 6 Basic Structure of a C Program (cont) #include int main() { printf(“Hello World!”); return 0; } C Program: Example: Hello world Instruction (function call) to output “Hello World!”

7. 7 int main() { return 0; } Example -- Count to 10 Print out numbers 0 to 9 set count to 0 while ( count is less than 10 ) { output count add 1 to count }

8. 8 #include int main() { return 0; } Example -- Count to 10 (cont) Print out numbers 0 to 9 set count to 0 while ( count is less than 10 ) { output count add 1 to count }

9. 9 #include /* Print out numbers 0 to 9 */ int main() { return 0; } Example -- Count to 10 (cont) Print out numbers 0 to 9 set count to 0 while ( count is less than 10 ) { output count add 1 to count } Comment

10. 10 #include /* Print out numbers 0 to 9 */ int main() { int count; return 0; } Example -- Count to 10 (cont) Print out numbers 0 to 9 set count to 0 while ( count is less than 10 ) { output count add 1 to count } Variable declaration

11. 11 #include /* Print out numbers 0 to 9 */ int main() { int count; count = 0; while ( count < 10 ) { printf(“%d\n”, count); count=count+1; } return 0; } Example -- Count to 10 (cont) Print out numbers 0 to 9 set count to 0 while ( count is less than 10 ) { output count add 1 to count }

12. 12 #include /* Print out numbers 0 to 9 */ int main() { int count; count = 0; while ( count < 10 ) { printf(“%d\n”, count); count=count+1; } return 0; } Example -- Count to 10 (cont) Print out numbers 0 to 9 set count to 0 while ( count is less than 10 ) { output count add 1 to count } Assignment of a value (right expression) to a variable (left).

13. 13 #include /* Print out numbers 0 to 9 */ int main() { int count; count = 0; while ( count < 10 ) { printf(“%d\n”, count); count=count+1; } return 0; } Example -- Count to 10 (cont) Print out numbers 0 to 9 set count to 0 while ( count is less than 10 ) { output count add 1 to count } No semi- colon here!

14. 14 #include /* Print out numbers 0 to 9 */ int main() { int count; count = 0; while ( count < 10 ) { printf(“%d\n”, count); count=count+1; } return 0; } Example -- Count to 10 (cont) Print out numbers 0 to 9 set count to 0 while ( count is less than 10 ) { output count add 1 to count }

15. 15 #include /* Print out numbers 0 to 9 */ int main() { int count; count = 0; while ( count < 10 ) { printf(“%d\n”, count); count=count+1; } return 0; } Example -- Count to 10 (cont) Print out numbers 0 to 9 set count to 0 while ( count is less than 10 ) { output count add 1 to count } Format string

16. 16 #include /* Print out numbers 0 to 9 */ int main() { int count; count = 0; while ( count < 10 ) { printf(“%d\n”, count); count=count+1; } return 0; } Example -- Count to 10 (cont) Print out numbers 0 to 9 set count to 0 while ( count is less than 10 ) { output count add 1 to count }

17. 17 Find the sign of a number output “Enter a number” input num if (num is less than 0) then { output num “ is -’ve” } else { output num “ is +’ve” } #include /* Find the sign of a number */ int main() { float num; printf(“Enter a number: “); scanf(“%f”, &num); if ( num < 0 ) { printf(“%f is -’ve\n”, num); } else { printf(“%f is +’ve\n”, num); } return 0; } Example -- What’s your sign?

18. 18 Find the sign of a number output “Enter a number” input num if (num is less than 0) then { output num “ is -’ve” } else { output num “ is +’ve” } #include /* Find the sign of a number */ int main() { float num; printf(“Enter a number: “); scanf(“%f”, &num); if ( num < 0 ) { printf(“%f is -’ve\n”, num); } else { printf(“%f is +’ve\n”, num); } return 0; } Example -- What’s your sign? (cont)

19. 19 Find the sign of a number output “Enter a number” input num if (num is less than 0) then { output num “ is -’ve” } else { output num “ is +’ve” } #include /* Find the sign of a number */ int main() { float num; printf(“Enter a number: “); scanf(“%f”, &num); if ( number < 0 ) { printf(“%f is -’ve\n”, num); } else { printf(“%f is +’ve\n”, num); } return 0; } Example -- What’s your sign? (cont)

20. 20 Find the sign of a number output “Enter a number” input num if (num is less than 0) then { output num “ is -’ve” } else { output num “ is +’ve” } #include /* Find the sign of a number */ int main() { float num; printf(“Enter a number: “); scanf(“%f”, &num); if ( num < 0 ) { printf(“%f is -’ve\n”, num); } else { printf(“%f is +’ve\n”, num); } return 0; } Example -- What’s your sign? (cont)

21. 21 Find the sign of a number output “Enter a number” input num if (num is less than 0) then { output num “ is -’ve” } else { output num “ is +’ve” } #include /* Find the sign of a number */ int main() { float num; printf(“Enter a number: “); scanf(“%f”, &num); if ( num < 0 ) { printf(“%f is -’ve\n”, num); } else { printf(“%f is +’ve\n”, num); } return 0; } Example -- What’s your sign? (cont)

22. 22 Topics Structure of a C program Values and variables Expressions Function calls Comments

23. 23 Values and Variables Basic Types: –Integers –Floating point numbers –Characters –Character Strings

24. 24 Basic Types: int and float Integers ( int ) 0 1 1000 -1 -10 666 Floating point numbers ( float ) 1.0.1 1.0e-1 1e1

25. 25 Basic Types: char Characters ( char ) ’a’ ’z’ ’A’ ’Z’ ’?’ ’@’ ’0’ ’9’ - Special Characters: preceded by \ ’\n’ ’\t’ ’\0’ ’\’’ ’\\’ etc.

26. 26 Basic Types: character string Character Strings (a string of char -s) Examples: –”Hi there!” –”Line 1\nLine 2\nLine 3” –”” –”\”\””

27. 27 Topics Structure of a C program Values and variables Expressions Function calls Comments

28. 28 Expressions Combine values using operators and function calls Return a value of a known type

29. 29 Arithmetic Expressions take arithmetic (numerical) values and return an arithmetic (numerical) value Are composed using the following operators: - (unary minus; a.k.a. “negation”) * (multiplication) / (division or quotient) % (modulus or remainder) + (addition) - (subtraction)

30. 30 Precedence in Expressions Defines the order in which an expression is evaluated

31. 31 Precedence in Expressions -- Example 1 + 2 * 3 - 4 / 5 = B stands for brackets, O for Order (exponents), D for division, M for multiplication, A for addition, and S for subtraction. B.O.D.M.A.S. 1 + (2 * 3) - (4 / 5)

32. 32 Precedence in Expressions – Example (cont) 6.2 1 + 2 * 3 - 4 / 5 = 1 + (2 * 3) - (4 / 5)

33. 33 Precedence in Expressions – Example (cont) 6.2 1 + 2 * 3 - 4 / 5 = 1 + (2 * 3) - (4 / 5)

34. 34 Precedence in Expressions – Example (cont) Integer division results in integer quotient 1 + 2 * 3 - 4 / 5 = 1 + (2 * 3) - (4 / 5)

35. 35 Precedence in Expressions – Example (cont) = 0 7 1 + 2 * 3 - 4 / 5 = 1 + (2 * 3) - (4 / 5)

36. 36 Precedence in Expressions – Example (cont) 7 1 + 2 * 3 - 4 / 5 = 1 + (2 * 3) - (4 / 5)

37. 37 int -s and float -s float is a “communicable” type Example: 1 + 2 * 3 - 4.0 / 5 = 1 + (2 * 3) - (4.0 / 5) = 1 + 6 - 0.8 = 6.2

38. 38 int -s and float -s – Example 2 (1 + 2) * (3 - 4) / 5 = ((1 + 2) * (3 - 4)) / 5 = (3 * -1) / 5 = -3 / 5 = 0

39. 39 int -s and float -s – Example 2 (cont) (1 + 2.0) * (3 - 4) / 5 = ((1 + 2.0) * (3 - 4)) / 5 = (3.0 * -1) / 5 = -3.0 / 5 = -0.6

40. 40 int -s and float -s – Example 3 (1 + 2.0) * ((3 - 4) / 5) = (1 + 2.0) * (-1 / 5) = 3.0 * 0 = 0.0

41. 41 Evaluate an expression set result to 1 + 2 * 3 - 4 / 5 output result #include Example -- Simple Expressions

42. 42 Evaluate an expression set result to 1 + 2 * 3 - 4 / 5 output result #include /* Evaluate an expression */ Example -- Simple Expressions (cont)

43. 43 Evaluate an expression set result to 1 + 2 * 3 - 4 / 5 output result #include /* Evaluate an expression */ int main() { return 0; } Example -- Simple Expressions (cont)

44. 44 Evaluate an expression set result to 1 + 2 * 3 - 4 / 5 output result #include /* Evaluate an expression */ int main() { float result; return 0; } Example -- Simple Expressions (cont)

45. 45 Evaluate an expression set result to 1 + 2 * 3 - 4 / 5 output result #include /* Evaluate an expression */ int main() { float result; result = 1 + 2 * 3 - 4 / 5; return 0; } Example -- Simple Expressions (cont)

46. 46 Evaluate an expression set result to 1 + 2 * 3 - 4 / 5 output result #include /* Evaluate an expression */ int main() { float result; result = 1 + 2 * 3 - 4 / 5; printf(“%f\n”, result); return 0; } Example -- Simple Expressions (cont)

47. 47 Topics Structure of a C program Values and variables Expressions Function calls Comments

48. 48 Function Calls Tell the computer to execute a series of C commands and (maybe) return a value –In algorithm-speak: An invocation of a named sequence of instructions Example: printf, scanf, sqrt

49. 49 Find the square root of x output ”Enter a number: " input x set myResult to result of squareRoot(x) output myResult Example --Find the square root

50. 50 Example -- Find the square root (cont) #include /* Find square root */ int main() { /* declare variables */ float x,myResult; /* output ”Enter a number: " */ printf(“Enter a number\n”); /* input x */ scanf(“%f”,&x); /* set myResult to result of squareRoot(x) */ myResult=sqrt(x); /* output myResult */ printf(“Result is %f\n”,myResult); return 0; }

51. 51 Topics Structure of a C program Values and variables Expressions Function calls Comments

52. 52 Comments Essential for documenting programs Run from a /* to the next */ Examples: /* THIS IS A COMMENT */ /* So is this*/ /* **...and this. ** */

53. 53 Comments (cont) Comments do not “nest” /*Comments start with a “/*” and end with a “*/” but they don’t nest! */

54. 54 Topics Structure of a C program Values and variables Expressions Function calls Comments

55. 55 Reading D&D: Chapter 2 –Sections 2.1 to 2.5