Question

{
int sum1, sum2;
sum1 = sum2 = 0;
for ( int i =1 ; i < = 10 ; i++)
if (1 % 2 = = 0)
sum1+ = i ;
else sum2+ = i ;

please make me understand the meaning of line line 2 and line 4
question is to write a programme that wil calculate sum of even numbers 1 to 10

Answer 1

Line 2 initializes the value of variables sum1 and sum2 to zero whereas line 4 will never execute the if part ie sum1 will always be 0 as 1%2=1 and 1 is never equal to zero(0).
So if statement is always false so only sum2 will be incremented not sum1 it remains same '0'.

Answer 2

Maybe phrasing it different will help:

int sum1 = 0;
int sum2 = 0;
for( int i = 1; i <= 10; i++ )
{
if( i % 2 == 0 )
sum1 += i;
else
sum2 += i;
}

I cleaned it up too, I hope.

Answer 3

biggest problem is the typo
if (1 % 2 = = 0)
instead of
if (i % 2 = = 0)

as rsmith has already corrected.

% is the modulo operator; a % b results in the remainder when you (integer-) divide a by b.

e. g. 1 % 2 is 1 (1 / 2 is 0 remainder 1), 3 % 2 is also 1 (3 / 2 is 1 remainder 1), 9 % 3 is 0 (because 9 / 3 leaves no remainder).

so what the line does is, is switches between numbers that are divisible without remainder by 2, and those that aren't. I. e. even and odd numbers.