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diff --git a/03-04.md b/03-04.md new file mode 100644 index 0000000..dfd1de5 --- /dev/null +++ b/03-04.md @@ -0,0 +1,172 @@ +[-> Notes 02/26](02-26.md) + +--- + +# Large Programs + +- When programs are long + - Need to split the file into several files + - Need to compile them together + - Example: + - We have files: main.c, list.c, file.c + - To compile: `gcc -o proj main.c list.c file.c` + +- Sharing global variables + - Define types in a `.h` file + - Declare global variables (do not initialize!) + - extern in a .h file + - Declare and initialize global variables + - in one of the .c file (e.g., the main one) + - Include the .h file in all the .c files which use any of the global variables: `#include "proj.h"` + +- Example: + - in `link.h`, declare (do not initialize!) global variables + - `extern NODE *head;` + - In main.c, include link.h, and declare and initialize global variables + +``` +#include "link.h" +NODE *head = (NODE *)NULL; +``` + +- In all the other .c files, just include link.h + - `#include "link.h"` + +- Use `makefile` to automate the compilation process +- Create a "makefile" file with instructions +- Command `make` will parse the makefile file and execute the appropraite command + - `<prompt> make proj1` + +- Example 1: + +``` +proj1: main1.c list1.c io1.c + gcc -o proj1 main1.c list1.c io1.c + ./proj1 filename +``` + +- Example 2: + +``` +proj2: main2.c list2.c thr2.c + gcc -o proj2 main2.c list2.c thr2.c -lpthread + ./proj2 filename1 filename2 +``` + +- The tab is important! (its the syntax) + +## Development Tools + +- Unix/Linux + - Environment and commands + - Tools - learn to use these!! + - vi + - grep + - gdb + - makefile + - shell script + +- Libraries + - Math + - String + - Memory + - Threads + +--- + +# Special Operators + +## Condtional Operator + +- The conditional operator `?:` takes three operands + - c ? r1 : r2 + - The value of the expression using the conditional operator is the value of either its second or third operand, depending on the value of the first operand + - Shorthand for: + +``` +if(c){ + //result value is r1 +} +else{ + //result value is r2 +} +``` + +- Examples + - In assignment: `x = (a < b) ? a : b;` + - x will be assigned the smallest value between a and b + +- Very useful for macros +- Examples: + - `#define MAX(a,b) (((a) > (b)) ? (a) : (b))` + - returns the max between the paramaters assigned to a and b + - `define ISLETTER(c) (((c) >= 'A' && (c) <= 'z') ? 1 : 0)` + - returns 1 if the value of assigned to c is a letter and returns 0 if not + +## Sequential Evaluation + +- The comma operator + - Evaluates its two operands in sequence, yeilding the value of the second operand as the value of the expression + - The value of the first is discarded + +- Example: + - In assignments: `x = (i += 2, a[i]);` -> `i += 2; x = a[i];` + - Parenthesis are important because precedence + +## Bitwise Operators + +- Positive integers are represented in the computer by standard binary numbers + - Examples: + +``` +short n = 13; +//in memory - 0000 0000 0000 1101 +//2^0 + 2^2 + 2^3 = 13 + +char c = 5; +//in memory - 0000 0101 +//2^0 + 2^2 = 5 +``` + +- Bitwise operators + - take operands of any integer type + - char, short, int, long + - but treat an operand as a collection of bits rather than a single number + +### Bitwise Negation + +- Bitwise negation + - Operand: `~` + - Application of `~` to an integer produces a value in which each bit of the operand has been replaced by its negation + - 0 -> 1 + - 1 -> 0 + - Example: + - ` n = 0000 0000 0000 1101` + - `~n = 1111 1111 1111 0010` + +### Bitwise Shift + +- Shift operators + - shift left: `<<` + - shift right: `>>` + - Take two integers operands + - The value on the left is the number to be shifted + - Viewed as a collection of bits that can move + - To avoid implementation problems, avoid negative numbers when shifting right + - The value on the right is a nonnegative number telling how far to move the bits + +- Operand + - `<<` shifts bits left + - `>>` shifts bits right +- The bits that "fall off the end" are lost +- The "emptied" positions are filled with zeros + +- Examples: + +``` +int n; // n is 0000 0000 0000 1101 +n << 1 //now n is 0000 0000 0001 1010 +n << 4 //now n is 0000 0000 1101 0000 +n >> 3 //now n is 0000 0000 0000 0001 +n << 4 //now n is 0000 0000 1101 0000 +``` |