confused with c++ program? [closed] - c++

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Closed 11 years ago.
I have compiled the following program and i know what it does, it takes ten numbers multiplies it my itself and then at the end add their total together.
#include <iostream>
using namespace std;
main()
{
int a[10];//1
int sumOfSquares = 0 ;//2
int i =0; //3`enter code here`
cout << "Please enter the ten numbers one by one " << endl;//4
for (i = 0 ; i < 10 ; i++)//5 dont get what this does,
// obviously its a for loop,
// but why does it increment i by one
{
cin >> a [i];//6 this means store the 10 numbers
// in array a and refer to it by the variable i
}
for (i = 0 ; i < 10 ; i++) //7 again i dont get why this is here
{
sumOfSquares = sumOfSquares + a[i]*a[i];//8
}
cout << "The sum of squares is "<< sumOfSquares << endl; //9
}

Answer 1

why does it increment i by one
Array indexes run from 0 to N-1, where N is the number of elements in the array.
i++ increments the value of i by 1 (equivalent to i = i + 1;). Incrementing i in the for loop is a construct for accessing each element of the array a (in order):
for (int i = 0; i < 10; i++)
{
a[i] = 2; /* just example */
}
is equivalent to:
a[0] = 2;
a[1] = 2;
...
a[9] = 2;
As others have commented, get a C++ book (see this SO question for a list of C++ books).

Answer 2

#include <iostream>
using namespace std;
main()
{
//declare space in memory for 10 numbers to be stored sequentially
//this is like having ten variables, a1, a2, a3, a4 but rather than having
//hardcoded names, you can say a[4] or rather i=4, a[i], to get variable a4.
int a[10];
int sumOfSquares = 0 ; //space for a number to be stored called sumOfSquares
int i =0; //space for a number to be stored called i
cout << "Please enter the ten numbers one by one " << endl; //print msg to screen
for (i = 0 ; i < 10 ; i++) //make i = 0; while i < 10 run this code! increase i by 1 each time
{
//a stores 10 numbers. put the number the user entered in space
//a[0] the first time, a[1] the second time, a[2] the third time etc etc.
cin >> a [i];
}
//run this code 10 times, with i=0 the first time, i=1 the second time,
// i=3 the third time etc etc.
for (i = 0 ; i < 10 ; i++)
{
//get the number at a[0] multiple it by the number at a[0]
//add it to value already in sumOfSquares so this number goes up and up and up.
//the second time through the loop get a[1] and multiply it by a[1].
sumOfSquares = sumOfSquares + a[i]*a[i];
}
//print answer to screen
cout << "The sum of squares is "<< sumOfSquares << endl; //9
}