Need help understanding swapping of integers

[Shyam Raj]

Edit: Apologies, thread should have been named as "Need help understanding swapping of characters"

Hello All,

I found a program on the internet that gets all possible combinations of a given string:

The code is as follows:

# include <stdio.h>
 
/* Function to swap values at two pointers */
void swap (char *x, char *y)
{
    char temp;
    temp = *x;
    *x = *y;
    *y = temp;
}
  
/* Function to print permutations of string
   This function takes three parameters:
   1. String
   2. Starting index of the string
   3. Ending index of the string. */
void permute(char *a, int i, int n)
{
   int j;
   if (i == n)
     printf("%s\n", a);
   else
   {
        for (j = i; j <= n; j++)
       {
          swap((a+i), (a+j));
          permute(a, i+1, n);
          swap((a+i), (a+j)); //backtrack
       }
   }
}
 
/* Driver program to test above functions */
int main()
{
   char a[] = "ABC"; 
   permute(a, 0, 2);
   getchar();
   return 0;
}

I don't understand what does swap((a+i), (a+j)); do?
'a' is supposed to be string and we add an integer to it? Is this correct? What result does this produce?

To understand (a+i) I wrote a small code as follows:

#include<stdio.h>
#include<conio.h>
int main(void)
{
    char a[] = "ABC";
    printf("%s", a);
    a+3;
    printf("\n\n%s", a);
    getch();
    return 0;
}

Both the print statements give ABC as the output. Could some one please clarify?

Thanks in advance.

[grumpy]

If a is a pointer (or an array) and i is an integer, then (a + i) is equivalent to (or a shorthand for) &a[i] - the address if the i'th element of a. This is true for all types in C (char, int, structs, float, double, etc).

[Salem]

How about

    char a[] = "ABC";
    printf("%s\n", a);
    swap(a+0,a+2);
    printf("%s\n", a);

[Shyam Raj]

If a is a pointer (or an array) and i is an integer, then (a + i) is equivalent to (or a shorthand for) &a[i] - the address if the i'th element of a. This is true for all types in C (char, int, structs, float, double, etc).

Thanks grumpy, I understood that now...

And thanks Salem as well .