Working with the Unix OS

C Programming – Basics
main.c
#include
#include
#include .calc.h.
#define MAXOP 10
main () {
...}
stack.c
#include
#include "calc.h"
#define MAXVAL 100
int sp=0;
double val[MAXVAL];
void push(double)
double pop(void){
...}
getop.c
#include
#include
#include "calc.h"
int getop(char s[]){
...}
Variables, Structure & Initialisation
Static variables remain in existence rather than coming and going each time the function is activated, i.e. permanent
storage within a single function.
C is not a block structured language in the sense of Pascal, because functions may not be defined within other
functions.
In the absence of explicit initialisation, external and static variables are guaranteed to be initialised to zero,
automatic and register variables have undefined initial values.
int days [] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
char pattern[] = "auld"; /* this is equivalent to */
char pattern[] = {'o', 'u','1','d','\0'};
Recursion
/* qsort: quick sort into ascending order */
void qsort(int v[], int left, int right)
{
int i, last;
void swap(int v[], int i, int j); /* you must implement it */
if (left >= right) /* do nothing if array contains */
return; /* fewer than two elements */
swap(v, left, (left+right)/2); /* move partition elem */
last = left;
for (i=left+1; i | .-| ---> |echo\0|
| .-| ---> |hello\0|
| .-| ---> |world\0|
| 0 |
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