Chapter 11-12 , Appendix D C Programs

1. Chapter 11-12 , Appendix D C Programs • Higher Level languages • Compilers • C programming • Converting C to Machine Code • C Compiler for LC-3

2. Higher Level Languages High Level Languages give us: • Symbolic Names • Expressions • Libraries of functions/subroutines • Abstraction of underlying hardware • Readability • Structure – help keep nasty bugs out

3. Translating Higher Level Program • Interpreters Translated to machine code as the program runs • Compilers Translated into a load module before program runs

4. Compiling C

5. Simple Example C Program /* * Program Name : countdown, our first C program * * Description : This program prompts the user to type in * a positive number and counts down from that number to 0, * displaying each number along the way. */ /* The next two lines are preprocessor directives */ #include <stdio.h> #define STOP 0 /* Function : main */ /* Description : prompt for input, then display countdown */ int main() { /* Variable declarations */ int counter; /* Holds intermediate count values */ int startPoint; /* Starting point for count down */ /* Prompt the user for input */ printf("===== Countdown Program =====\n"); printf("Enter a positive integer: "); scanf("%d", &startPoint); /* Count down from the input number to 0 */ for (counter = startPoint; counter >= STOP; counter--) { printf("%d\n", counter); } return 0 }

6. Terms, Etc. • Pre processor directives #define #include • Header Files <stdio.h> • Data Types int char double • Scope Local Global • Variable Initiation Local – not initialized Global – initialized to 0

7. Scope #include <stdio.h> int globalVar = 2; /* This variable is global */ int main() { int localVar = 3; /* This variable is local to main */ printf("Global %d Local %d\n", globalVar, localVar); { int localVar = 4; /* Local to this sub-block */ printf("Global %d Local %d\n", globalVar, localVar); } printf("Global %d Local %d\n", globalVar, localVar); return 0 }

8. Pointers - IMPORTANT • A pointer is a variable which contains the address in memory of another variable. • We can have a pointer to any variable type. • The unary or monadic operator & gives the ``address of a variable''. • The indirection or dereference operator * gives the ``contents of an object pointed • to by a pointer variable''. • To declare a pointer to a variable:int *pointer; Note: ip = ip + 1 actually increments ip by 4. Why?