Need help in algorithm/coding
Hi. I am new in C programming. I am tasked to complete a program. The hardest part in programming is to understand the logic of a program. Please explain to how and why the algorithm works. I have commented the parts that i need know of/needs help in green. Your help is so much appreciated. Thanks.
These are the requirements:
Complete the following C program so that it displays the addresses of
1. functions addr, f1, f2, and main;
2. all string literals such as "Hello, world!";
3. all initialized global variables;
4. all un-initialized global variables;
5. all dynamically allocated memories;
6. all formal parameters in functions;
7. all local variables;
8. start and end of its command line arguments;
9. start and end of its environment (variables and values).
The sample program is shown below.
Code:
// To declare package/lib
#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <string.h>
extern char **environ;
int global_x = 10; // initialised global variable
int global_y; // un-initialised global variable
char global_array1[] = "Hello, world!"; // initialised global array
char global_array2[10]; // un-initialised global array
char *global_pointer1 = "bye!"; // global pointer to a string literal
char *global_pointer2; // un-initialised global pointer
float global_float = 100.1; // initialised global variable
double global_double; // un-initialised global variable
// To define global variable
#define ONEGB 1073741824
#define ONEMB 1048576
#define ONEKB 1024
char *addr(unsigned long a)
{
unsigned long r; // remainder
/* ---> Why does division have to do with finding a address??
r = (unsigned long) a;
int gb = (int) ( r / ONEGB );
r -= gb * ONEGB;
int mb = (int) ( r / ONEMB );
r -= mb * ONEMB;
int kb = (int) ( r / ONEKB );
r -= kb * ONEKB;
int b = (int) ( r );
*/
// To dynamically allocated memory
char *p = malloc(64);
// To store value in p. --> Why does"%4dGB" means and how it works. Why can't
to be just %d??
sprintf(p, "%4dGB, %4dMB, %4dKB, %4d", gb, mb, kb, b);
return p;
}
int f2(int x)
{
char * f2_p;
int f2_x = 21;
f2_p = malloc(1000);
// A BLANK part. What do i need to do here????
.....
// What is L:?? Is it a variable to be declared in the BLANK part?
L: f2_x = 10;
return f2_x;
}
// To declare a function
void f1(int x1, int x2, float x3, char x4, double x5, int x6)
{
int f1_x = 10;
int f1_y;
char *f1_p1 = "This is inside f1"; // Create pointer to another string
char *f1_p2;
f1_p2 = malloc(100);
..... // What do i need to do here??
f1_y = f2(10);
return;
}
main(int argc, char *argv[])
{
/* What do i need to do here??
.....
f1( .... );
*/
exit(0);
}
