What is the purpose of the gate2011 Program in the C programming language?

[sam topper.]

#include<stdio.h>
void main()
{
char c[]="gate2011";
char *p=c;
printf("%s",p+p[3]-p[1]);
}

 

[CompuChip]

Doesn't look like rocket science. What do you think will happen? What actually happens when you run it?

 

[jk22]

It apparently takes the adress of the string + 65-61= adr + 4. Now I don't know but this seems not aligned, but it means maybe adr + 4 bytes, hence it maybe prints '2011', but I have not checked this for real.

 

[CompuChip]

The trick is the way that pointers and arrays are equivalent in C++.
If you have an array

int[] a;

then a is a pointer to an int, and &a[4] and *(a + 4) both point to address of the 5th array element.
So the pointer p points at the beginning of the string, p[4] - p[1] is the length of the memory block used by the first four characters and the sum is a pointer to the place in memory where the '2' is stored. Since strings are terminated by a null (\0) the statement is equivalent to

    char p[] = { '2', '0', '1', '1', '\0' };
    printf("%s", p);

You could actually reach the same thing through

#include<stdio.h>
void main()
{
    char c[]="gate2011";
    // No need to introduce a new name, c is already a char*
    // char* p = c; 
    printf("%s", (c + 4));
}

 

[LudusRex]

The "gate2011" Program is a program written in the C programming language that utilizes the concept of pointer arithmetic to print out a specific string. The program first declares a character array named "c" with the value "gate2011". Then, a pointer variable "p" is assigned to point to the first element of the array. Using pointer arithmetic, the program accesses the elements of the array and prints out the string "gate2011" by adding the value of the third element of the array (which is 'e') to the address of the pointer and subtracting the value of the second element of the array (which is 'a'). This results in the pointer pointing to the fourth element of the array, which is 't'. This clever use of pointer arithmetic allows the program to print out the desired string without explicitly using the string itself.