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  1. #include <stdio.h>
  2.  
  3. void func(int *p);
  4. void funcar(int ar[]);
  5.  
  6. int main(void) {
  7. 	int a[10] = {0,1,2,3,4,5,6,7,8,9};
  8. 	int *b;
  9. 	b = a;						/* Valid */
  10. 	// printf("%d", *b[1]); 	// [X]Wrong, error: invalid type argument of unary ‘*’ (have ‘int’)
  11. 	printf("%d\n", b[1]);		// array name/label itself acts as the pointer to array
  12. 	printf("%d\n", *(b+2));	// another way of representing 
  13. 	int q[10];
  14. 	/* However, This is not valid */
  15. 	// q = a;			// [X]Wrong
  16.  
  17. 	int c = 10;
  18. 	// int *d = c;		// [X]Wrong
  19. 	int *d;
  20. 	d = &c;
  21. 	// int *d = &c;		// alternate way to assign, confusing
  22. 	// int *b = &a[0];
  23. 	printf("%p %d\n", &c, *d);
  24. 	printf("%p %d\n", d, *d);
  25.  
  26. 	char *str = "Ninechars";
  27. 	printf("Start\n");
  28. 	printf("%s\n", str);
  29. 	printf("%p\n", str);	// address of first char of str
  30. 	printf("%p\n", str+1);	// address of second char of str
  31. 	// printf("%s\n", str[1]);	// [segfault] warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘int’ [TODO]
  32. 	printf("%p\n", &str);	// address to head of the string? NO, address of the pointer var str
  33. 	printf("%p\n", &str+1);	// [TODO], difference of 8bytes b/w this and previous address value? [WHY]?
  34. 	printf("%d\n", *str);	// what integer is this? -> whatever can be made from 'N'=78
  35. 	printf("%d\n", *(str+1));	// 'i'=105, but why is it taking single byte ints [TODO]
  36. 	printf("%ld\n", sizeof(1));	// 4 bytes, as expected
  37. 	// printf("%s\n", *str);	// [?]Wrong, [HOW][WHY], format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘int’[TODO]
  38. 	printf("End\n");
  39. 	// int *f[5] = {213,214,215,216,217};	// [X]Wrong, this is array of pointers
  40. 										// so the array should contain ptrs not values
  41. 	char *str2[3] = {"A","B","C"};
  42. 	printf("%s\n", *str2);
  43. 	printf("%s\n", *(str2+1));
  44. 	// printf("%s\n", str2);	// [X]Wrong, expects argument of type ‘char *’, but argument 2 has type ‘char **’
  45.  
  46. 	int * i, * l, * s;		// three pointers-to-int
  47.  	int * x, y, z;			// x is a pointer, y and z are ints
  48.  
  49. 	func(a);
  50. 	funcar(a);	// passing the entire array
  51. 	return 0;
  52. }
  53.  
  54. void func(int *p)	// passing an array as a pointer
  55. {
  56. 	printf("%d\n", p[0]);
  57. 	printf("%d\n", p[7]);
  58. }
  59.  
  60. void funcar(int ar[])	// passing an entire array, not memory efficient
  61. {
  62. 	// ^even if I give ar[4] as func arg it still displays ar[5] correctly
  63. 	printf("%d\n", ar[3]);
  64. 	printf("%d\n", ar[5]);
  65. }
Success #stdin #stdout 0s 2292KB
comments (?)
stdin 
Standard input is empty
stdout 
1
2
0xbf839240 10
0xbf839240 10
Start
Ninechars
0x8048777
0x8048778
0xbf839244
0xbf839248
78
105
4
End
A
B
0
7
3
5
https://ideone.com/ryag80
language:
C (gcc 8.3)
created:
10 years ago
visibility:
public

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