1. CSE1301 Computer Programming Lecture 2: Introduction to C Joselito (Joey) Chua http://www.csse.monash.edu.au/~jjchua

2. Topics Basic structure of a C program C “baby-talk” phrases printf(“Da-da-da”);

3. 0 or 1 Recall:

4. Machine Language 10100110 01110110 00100110 00000000 11111010 01001110 10100110 11100110 10010110 11001110 00101110 10100110 01001110 11111010 01100110 01001110 10000110 etc...

5. High-Level Language Compilers and linkers translate a high level program into executable machine code. #include int main() { printf(“Da-da-da”); return 0; } Source code Executable code 10100110 01110110 00100110 00000000 11111010 01001110 10100110 11100110 10010110 11001110 00101110 10100110 01001110 11111010 01100110 01001110 10000110 etc...

6. Why C? Structured language Standard library exists, allowing portability –See D&D 2/e Appendix B (web links in D&D 3/e) –Forouzan & Gilberg Appendix F Wide availability on a variety of computers Low level activities possible It can produce lean and efficient code Widely used

7. History of C CPL Combined Programming Language (Barron et al., 1963) BCPL Basic CPL (Richards, 1969) B (Thompson, 1970) C K&R C (Ritchie, 1972) ANSI C American National Standards Institute C (X3J11, 1989) C9X (JTC1/SC22/WG14, ISO/IEC 9899)

8. Basic Structure of a C Program output “Da-da-da” Instructions: #include int main() { printf(“Da-da-da”); return 0; } C Program: Example: Da-da-da

9. Basic Structure of a C Program #include int main() { printf(“Da-da-da”); return 0; } C Program: “Skeleton” Example: Da-da-da

10. Basic Structure of a C Program #include int main() { printf(“Da-da-da”); return 0; } C Program: void main() { } Also: Not recommended Example: Da-da-da

11. Basic Structure of a C Program #include int main() { printf(“Da-da-da”); return 0; } C Program: main() { return 0; } Also: Assumes int Example: Da-da-da

12. Basic Structure of a C Program #include int main() { printf(“Da-da-da”); return 0; } C Program: main() { return 0; } Also: Warning messages: “Return value expected” Example: Da-da-da

13. Basic Structure of a C Program #include int main() { printf(“Da-da-da”); return 0; } C Program: Includes standard input / output library of functions. Read: “Hash-include” Example: Da-da-da

14. Basic Structure of a C Program #include int main() { printf(“Da-da-da”); return 0; } C Program: Brackets mark the beginning and end of a block of instructions. Example: Da-da-da

15. Basic Structure of a C Program #include int main() { printf(“Da-da-da”); return 0; } C Program: Instruction (function call) to output “Da-da-da” Example: Da-da-da

16. Basic Structure of a C Program #include int main() { printf(“Da-da-da”); return 0; } C Program: “Statements” (lines of instructions) end with a semi-colon ( ; ) Example: Da-da-da

17. Simple C Phrases Example 1: Float let x be equal to 4.5 output the value of x Instructions: #include int main() { float x; x = 4.5; printf(“%f”, x); return 0; } C Program:

18. Simple C Phrases Example 1: Float #include int main() { float x; x = 4.5; printf(“%f”, x); return 0; } C Program: Declares that x is a variable which can be assigned a numerical value.

19. Simple C Phrases Example 1: Float #include int main() { float x; x = 4.5; printf(“%f”, x); return 0; } C Program: Assigns the value 4.5 into the variable x. (Remember: “right value is assigned to left variable”)

20. Simple C Phrases Example 1: Float #include int main() { float x; x = 4.5; printf(“%f”, x); return 0; } C Program: Outputs the value of x. (“ %f ” for float)

21. Simple C Phrases Example 2: Sum input the value of x input the value of y output “The sum is “ output the value of x + y output a new line Instructions: #include int main() { float x; float y; scanf(“%f”, &x); scanf(“%f”, &y); printf(“The sum is “); printf(“%f”, x + y); printf(“\n”); return 0; } C Program:

22. x and y are both numeric variables #include int main() { float x; float y; scanf(“%f”, &x); scanf(“%f”, &y); printf(“The sum is “); printf(“%f”, x + y); printf(“\n”); return 0; } C Program: Simple C Phrases Example 2: Sum

23. Input the values of x and y respectively (note the ampersand!) #include int main() { float x; float y; scanf(“%f”, &x); scanf(“%f”, &y); printf(“The sum is “); printf(“%f”, x + y); printf(“\n”); return 0; } C Program: Simple C Phrases Example 2: Sum

24. Outputs the string: “The sum is “ #include int main() { float x; float y; scanf(“%f”, &x); scanf(“%f”, &y); printf(“The sum is “); printf(“%f”, x + y); printf(“\n”); return 0; } C Program: Simple C Phrases Example 2: Sum

25. Outputs the sum x + y #include int main() { float x; float y; scanf(“%f”, &x); scanf(“%f”, &y); printf(“The sum is “); printf(“%f”, x + y); printf(“\n”); return 0; } C Program: Simple C Phrases Example 2: Sum

26. Outputs a newline #include int main() { float x; float y; scanf(“%f”, &x); scanf(“%f”, &y); printf(“The sum is “); printf(“%f”, x + y); printf(“\n”); return 0; } C Program: Simple C Phrases Example 2: Sum

27. Simple C Phrases: “if” #include int main() { char name[50]; float mark; printf("What is your name? "); scanf("%s", name); printf("What is your mark? "); scanf("%f", &mark); printf("\n"); printf("Hi, "); printf("%s", name); printf("!\n"); /* The next output depends on the mark. */ if (mark < 50) { printf("Sorry. You failed.\n"); } else { printf("Yey! You passed!\n"); } return 0; } Example 3: Mark

28. Simple C Phrases: “if” #include int main() { char name[50]; float mark; printf("What is your name? "); scanf("%s", name); printf("What is your mark? "); scanf("%f", &mark); printf("\n"); printf("Hi, "); printf("%s", name); printf("!\n"); Example 3: Mark /* The next output depends on the mark. */ if (mark < 50) { printf("Sorry. You failed.\n"); } else { printf("Yey! You passed!\n"); } return 0; } Declares that name is a variable which can contain a “string” (i.e. words, names, etc.)

29. /* The next output depends on the mark. */ if (mark < 50) { printf("Sorry. You failed.\n"); } else { printf("Yey! You passed!\n"); } return 0; } Simple C Phrases: “if” #include int main() { char name[50]; float mark; printf("What is your name? "); scanf("%s", name); printf("What is your mark? "); scanf("%f", &mark); printf("\n"); printf("Hi, "); printf("%s", name); printf("!\n"); Example 3: Mark Outputs a “prompt” so the user knows what the program wants.

30. /* The next output depends on the mark. */ if (mark < 50) { printf("Sorry. You failed.\n"); } else { printf("Yey! You passed!\n"); } return 0; } Simple C Phrases: “if” #include int main() { char name[50]; float mark; printf("What is your name? "); scanf("%s", name); printf("What is your mark? "); scanf("%f", &mark); printf("\n"); printf("Hi, "); printf("%s", name); printf("!\n"); Example 3: Mark Inputs the string content of the variable name. (Note: no ampersand!)

31. /* The next output depends on the mark. */ if (mark < 50) { printf("Sorry. You failed.\n"); } else { printf("Yey! You passed!\n"); } return 0; } Simple C Phrases: “if” #include int main() { char name[50]; float mark; printf("What is your name? "); scanf("%s", name); printf("What is your mark? "); scanf("%f", &mark); printf("\n"); printf("Hi, "); printf("%s", name); printf("!\n"); Example 3: Mark (The usual. Note the ampersand for floats!)

32. /* The next output depends on the mark. */ if (mark < 50) { printf("Sorry. You failed.\n"); } else { printf("Yey! You passed!\n"); } return 0; } Simple C Phrases: “if” #include int main() { char name[50]; float mark; printf("What is your name? "); scanf("%s", name); printf("What is your mark? "); scanf("%f", &mark); printf("\n"); printf("Hi, "); printf("%s", name); printf("!\n"); Example 3: Mark Outputs the string name. (Note the “%s”)

33. /* The next output depends on the mark. */ if (mark < 50) { printf("Sorry. You failed.\n"); } else { printf("Yey! You passed!\n"); } return 0; } Simple C Phrases: “if” #include int main() { char name[50]; float mark; printf("What is your name? "); scanf("%s", name); printf("What is your mark? "); scanf("%f", &mark); printf("\n"); printf("Hi, "); printf("%s", name); printf("!\n"); Example 3: Mark Comments: everything between /* and */ are ignored by the compiler.

34. Simple C Phrases: “if” #include int main() { char name[50]; float mark; printf("What is your name? "); scanf("%s", name); printf("What is your mark? "); scanf("%f", &mark); printf("\n"); printf("Hi, "); printf("%s", name); printf("!\n"); Example 3: Mark This block of instructions is performed if the comparison is true. /* The next output depends on the mark. */ if (mark < 50) { printf("Sorry. You failed.\n"); } else { printf("Yey! You passed!\n"); } return 0; }

35. Simple C Phrases: “if” #include int main() { char name[50]; float mark; printf("What is your name? "); scanf("%s", name); printf("What is your mark? "); scanf("%f", &mark); printf("\n"); printf("Hi, "); printf("%s", name); printf("!\n"); Example 3: Mark This block of instructions is performed if the comparison is false. /* The next output depends on the mark. */ if (mark < 50) { printf("Sorry. You failed.\n"); } else { printf("Yey! You passed!\n"); } return 0; }

36. Summary Basic structure of a C program Simple C “phrases” –Declaring numerical variables (floats) –Declaring string variables –Input (scanf) and Output (printf) –comments –The “if...else...” condition Readings: Forouzan & Gilberg, Chapter 1