Question

c++ only. Please follow directions.

What does the following program print and why? Comment each line of code to explain what it is doing.  

#include <iostream>
using namespace std;

int main()
{
int track[ ] = { 10, 20, 30, 40 };
int * ptr;

ptr = track;
track[1] += 30;
cout << * ptr << " ";
*ptr -= 10;
ptr++;
cout << * ptr << " ";
ptr += 2;
cout << * ptr << " ";
cout << track[ 0 ] << endl;

return( 0 );
}

Answer 1

#include <iostream>
using namespace std;

int main()
{
int track[ ] = { 10, 20, 30, 40 };
int * ptr;

ptr = track;
// this changes the value of 20 to 20+30 = 50
track[1] += 30;

// As ptr points to start of the array track
// *ptr prints 10
cout << * ptr << " ";

// this changes track[0]=track[0]-10 = 0
*ptr -= 10;

// ptr points to track[1] 
ptr++;

// prints the value of track[1]
// prints 50
cout << * ptr << " ";

// ptr points to track[3]
ptr += 2;

// this prints value of track[3]
// i.e 40
cout << * ptr << " ";

// track[0] is 0
// so it prints 0
cout << track[ 0 ] << endl;

return( 0 );
}

10 50 40 0

Note: Please follow comments in code