This is a C program that uses pointer arithmetic to calculate the length of a string.
The string "GATECSIT2017" is stored in a character pointer variable c. A pointer variable p is also defined and it is assigned the value of the pointer c.
In the printf statement, the expression (c+2[p]-6[p]-1) is used to calculate the length of the string.
The expression c+2[p] is equivalent to c+2[c], which means that it is referencing the 3rd character of the string (index 2) which is 'T'
The expression 6[p] is equivalent to 6[c], which means that it is referencing the 7th character of the string (index 6) which is 'I'
So, the expression c+2[p]-6[p]-1 is equivalent to 'T'-'I'-1 which evaluates to -9.
The printf statement prints the value of this expression as an integer, which is -9.
It is important to note that this code will not give the correct length of the string, as the strlen() function is not used in the program, and the expression used to calculate the length is not correct and it will always return -9.