View source for SE250:lab-2:srag014

This second lab is primarily based on pointers.

===Task 1===
 #include <stdio.h>
 int main(){
       int *ip;
       printf("%d\n", sizeof(ip));
 }

Size of all pointers no matter the data type or OS, they all had the same value of 4.
I thought the value will vary in Linux but guess it doesnt.

===Task 2===
In task 2 we had to declare two variables x and y and print out their addresses and also the difference between these addresses <br>

 #include <stdio.h>
 int main(void){
         int x;
         int y;
         printf("&x=%p,&y=%p,diff=%ld\n",&x,&y,(long)(&x-&y));
         printf("&x=%p,&y=%p,diff=%ld\n",&x,&y,((long)&x-(long)&y));
 }

For Windows:<br>
&x=0023FDB0        &y=0023FDA4        diff=3  <br>
&x=0023FDB0        &y=0023FDA4        diff=12 <br>

For Linux:<br>
&x = 0xffa75710 &y = 0xffa7570c, difference = 1 <br>
&x = 0xffa75710 &y = 0xffa7570c, difference = 4 <br>
Note: Had some problems getting into linux as my pc didnt bring up my home drive so had to look at neighbours comp.

===Task 3===
In task 3 we introduce the statement char arr[4] between the x and y variables.
 #include <stdio.h>
 int main(void){
 int x;
 char arr[4];	
 int y;
 printf("enter needed statement here",)
 }

Using Windows,we had to find:
*Sizeof array: 4
*Address of array: 0012FF54
*Value of &arr:1245012
*Value of arr+4:1245016
*Value of &arr[4]:1245016

Varying the size of the array from 0 to 10, and recording the difference between &x and &y.

 #include <stdio.h>
 int main(){
 int x;
 char arr["enter number here"];
 int y;
 printf("&x=%p,&y=%p,diff=%ld\n",&x,&y,(long)(&x-&y));
 printf("&x=%p,&y=%p,diff=%ld\n",&x,&y,((long)&x-(long)&y));
 }<br>

Array sizes and their differences:<br>
0|Not Applicable<br>
1|6,24<br>
2|6,24<br>
3|6,24<br>
4|6,24<br>
5|7,28<br>
6|7,28<br>
7|7,28<br>
8|7,28<br>
9|8,32<br>
10|8,32<br>
Note: No results for linux due to me having technical issues.

Next step is reverting back to array size 4 and setting x and y to 0 and arr[4] to 10 and printing out values 

 #include <stdio.h>
 int main(){
 int x=0;
 char arr[4] = {10};	
 int y=0;
 printf("Value of x=%d\nValue of y=%d\n", x, y);
 }<br>

x=0<br>  
y=0<br>
Note: not sure if its correct.

===Task 4===
Declaring x and y as global variables.

 #include <stdio.h>
 int y;
 int x;
 int main(){
 char arr["enter number here"];
 printf("&x=%p,&y=%p,diff=%ld\n",&x,&y,(long)(&x-&y));
 printf("&x=%p,&y=%p,diff=%ld\n",&x,&y,((long)&x-(long)&y));
 }<br>

Array sizes and their differences:<br>
0|Not Applicable<br>
1|1,4<br>
2|1,4<br>
3|1,4<br>
4|1,4<br>
5|1,4<br>
6|1,4<br>
7|1,4<br>
8|1,4<br>
9|1,4<br>
10|1,4<br>
Note:Are the results meant to be the same??Also i get different results on different computers which is expected i suppose.  <br>

===Task 5===
 int *p1, *p2;
 { int q; p1 = &q; }
 { int r; p2 = &r; }<BR>

I think the values of p1 and p2 will be whatever the address if q and r are since they will be pointing at p and q respectively.<br>

===Task 6===
Program woudnt compile in visual studio.

===Task 7===
 #include <stdio.h>
 struct {
 char my_char;
 short my_short;
 int my_int;
 long my_long;
 float my_float;
 double my_double;
 } my_struct;
 int main ()
 {   
 printf( "&my struct = %p\n", my_struct );
 printf( "offsets:\n"
 "my_char: %ld\n"
 "my_short: %ld\n"
 "my_int: %ld\n"
 "my_long: %ld\n"
 "my_float: %ld\n"
 "my_double: %ld\n",
 (long)&my_struct - (long)&my_struct.my_char,
 (long)&my_struct - (long)&my_struct.my_short,
 (long)&my_struct - (long)&my_struct.my_int,
 (long)&my_struct - (long)&my_struct.my_long,
 (long)&my_struct - (long)&my_struct.my_float,
 (long)&my_struct - (long)&my_struct.my_double );
 }<br>

Results:<BR>
offsets:<BR>
my_char: 0<BR>
my_short: -2<BR>
my_int: -4<BR>
my_long: -8<BR>
my_float: -12<BR>
my_double: -16<BR>

===Task 8===

 #include <stdio.h>
 union {
 char my_char;
 short my_short;
 int my_int;
 long my_long;
 float my_float;
 double my_double;
 } my_union;
 int main ()
 {   
 printf( "&my struct = %p\n", my_union );
 printf( "offsets:\n"
 "my_char: %ld\n"
 "my_short: %ld\n"
 "my_int: %ld\n"
 "my_long: %ld\n"
 "my_float: %ld\n"
 "my_double: %ld\n",
 (long)&my_union - (long)&my_union.my_char,
 (long)&my_union - (long)&my_union.my_short,
 (long)&my_union - (long)&my_union.my_int,
 (long)&my_union - (long)&my_union.my_long,
 (long)&my_union - (long)&my_union.my_float,
 (long)&my_union - (long)&my_union.my_double );
 }<br>

Results from using union:<br>
offsets:<br>
my_char: 0<br>
my_short: 0<br>
my_int: 0<br>
my_long: 0<br>
my_float: 0<br>
my_double: 0<br>

===Task 9===

 #include <stdio.h>
 int main()
 {
 char *sp1, *sp2, *sp3;
 sp1 = malloc( 10 );
 printf("sp1=%p\n",sp1);	
 sp2 = malloc( 10 );
 printf("sp2=%p\n",sp2);	
 free( sp1 );
 sp3 = malloc( 10 );
 printf("sp3=%p\n",sp3);
 printf("sp1=%p\n",sp1);	
 }<br>


Results (windows):<br>
sp1=00924B28<br>
sp2=00922288<br>
sp3=009222C0<br>
sp1=00924B28<br>
Results(linux):<br>
sp1= 0xff809728<br>
sp2= 0xff809724<br>
sp3= 0xff809720<br>
sp1= 0xff809728<br>