FOR LOOP Help! Sum of the Multiples

[Tstan]

Trying to make a formula to show the Sum of the Multiples of a given number less than 100. Here is my code I cannot figure it out and get it to work right! Please Help

 cout << "What multiples are we adding? ";
   int multiple;
   cin >> multiple;
   for (int sum = multiple; sum < 100; sum + sum)
      cout << "The sum of multiples of "
           << multiple
           << "less than 100 are: "
           << sum
           << endl;

[giblit]

shouldn't line 6 be << sum - sum? since you are only adding the two "sums" together and not getting a new value for multiple. Also try sum += sum in the for loop.

[MrPatsr]

From just looking at your code your not incrementing anything so sum never changes; ( sum += sum ) after the for loop than try to cout and if that does not work try a function and return a value for each time through the loop.

[Tstan]

I have tried sum += sum and it gives me 3 lines going up to 100. but I am looking for the sum of those multiples. which lets say for 5 should be 950. but when I do 5 it goes 5 10 20 40 80 thats it when I want it to show the SUM of all the multiples.

[giblit]

are you talking about 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 + 13 + 14 + 15 + 16 + 17....? Because currently you are just doubling the last value..

[Tstan]

I need it to do this
lets say I enter the value of 5
I need it to show the sum of the multiples of 5 being
5+10+15+20+25+30+35+40+45+50+55+60+65+70+75+80+85+90+95=950 and I need it to show that answer.

[giblit]

Maybe try something like this?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

#include <iostream> #include <limits> int main() { auto input = 0 , total = 0; do { std::cout << "Please enter a value between 1 and 100\n> " << std::flush; std::cin >> input; std::cin.clear(); std::cin.ignore( std::numeric_limits<std::streamsize>::max() , '\n' ); } while( input == 0 || input > 100 ); for( auto i = 0 ; i < 100; i += input) { total += i; } std::cout << total << std::endl; }

Please enter a value between 1 and 100 > 5 950 Process returned 0 (0x0) execution time : 1.283 s Press any key to continue.

See the for loop? I am incrementing i by the inputed value then adding that to the total. I got a result of 950 when I added it up.

[Tstan]

cout << "What multiples are we adding? ";
int multiple;
int I;
int total;
cin >> multiple;
while ( multiple == 0 || multiple > 100);
for (int I = 0; multiple < 100; I += multiple)
cout << "The sum of multiples of "
<< multiple
<< " less than 100 are: "
<< I
<< endl;
{
total += I;
}
return 0;
I am trying to use what you are showing me when I try to run the program it gives me an infinite loop and the program wont close it keeps counting in increments of whatever the input is forever.

[giblit]

first of all you are forgetting the do all you have is a while statement.
do/while loops run a minimum of 1 time. while loops run a minimum of 0 times. Also you are not initializing a value of total do total = 0 when you declare it so it is initialzed with a value of 0. Otherwise when you cal total += i it is going to be an undefined value. Also you should try to indent like I have done. after each curly brace you move to the right 4 spaces or a horizontal tab. Also it should be i < 100 because multiple never changes. The I is what is changing the I becomes the 5 , 10 , 15 ect..because you are adding the value entered to i each time. Think about it.
for( int i = 0; i < 100; i += multiple) says this multiple == 5.
i == 0;
i == 5;
i == 10;
i == 15;
i == 20;
i == 25;
i == 30;
.....
i == 100;
i cannot be greater than 100 so the loop ends.

[Tstan]

Ok I am trying to do those things and it is not working for me. Thank you tho! I will have to go in a ask someone in my class

[giblit]

Show me what you have? I told you what lines have the errors.
Line 4 , 5 , ( 0 missing do before first cout so I call it position 0) , line 6 , line 7-10.

[Tstan]

int main()
{
cout << "What multiples are we adding? ";
int multiple;
int I;
int total;
cin >> multiple;
do
{
total = 0;
}
while ( multiple == 0 || multiple > 100);
for (int I = 0; I < 100; I += multiple)
cout << "The sum of multiples of "
<< multiple
<< " less than 100 are: "
<< I
<< endl;
{
total += I;
}
return 0;

}
Now it counts all the way to 95 then stops rather than showing the sum. Thank you for your willingness to help.

[giblit]

Wrong. It is counting to 100. The problem is you are not outputting the last one. As you can see in the for loop you out then add to the value of total.
A Quick fix would be to output the total after the for loop ends like I did.

for(....)
{
...
}
std::cout << total << std::endl;

Edit let me fix your code up a lil with notes...

int main()
{
//cout << "What multiples are we adding? ";
int multiple;
int I;
/*int total;*/ int total = 0;
//cin >> multiple;
do
{
//total = 0;
std::cout << "What multiples are we adding( 1 - 100 );
std::cin >> multiple; 
}
while ( multiple < 1 || multiple > 100); //If you do not clear and ignore you 
//will have a major problem if someone inputs a letter.
for (int I = 0; I < 100; I += multiple){
/*cout << "The sum of multiples of "
<< multiple
<< " less than 100 are: "
<< I
<< endl;*/
total += I;
std::cout << "The sum of multiples of " << multiple << " less than 100 are "
<< I << " Which has a total so far of " << total << std::endl;
//{
//total += I;
}
return 0;

} 

Also may I suggest you learn proper indenting.

[Tstan]

ok so i changed it to output the totals and it gives me
What multiples are we adding? 5
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0
The sum of multiples of 5 less than 100 are: 0

[giblit]

I just updated my last post check it out.

[Tstan]

Ok I will type this out without comments and hopeful it will work. I appreciate your help.

[Tstan]

int main()
{
int multiple;

int total = 0;
cin >> multiple;
do
{
cout << "What multiples are we adding? ";
cin >> multiple;
}
while (multiple < 1 || multiple > 100);
for (int I = 0; I < 100; I += multiple)
{
total += I;
cout << "The sum of of multiples of " << multiple << " less than 100 are " << total << endl;
}
return 0;
}
I am now getting to where it is showing me this response.
What multiples are we adding? 5
The sum of of multiples of 5 less than 100 are 0
The sum of of multiples of 5 less than 100 are 5
The sum of of multiples of 5 less than 100 are 15
The sum of of multiples of 5 less than 100 are 30
The sum of of multiples of 5 less than 100 are 50
The sum of of multiples of 5 less than 100 are 75
The sum of of multiples of 5 less than 100 are 105
The sum of of multiples of 5 less than 100 are 140
The sum of of multiples of 5 less than 100 are 180
The sum of of multiples of 5 less than 100 are 225
The sum of of multiples of 5 less than 100 are 275
The sum of of multiples of 5 less than 100 are 330
The sum of of multiples of 5 less than 100 are 390
The sum of of multiples of 5 less than 100 are 455
The sum of of multiples of 5 less than 100 are 525
The sum of of multiples of 5 less than 100 are 600
The sum of of multiples of 5 less than 100 are 680
The sum of of multiples of 5 less than 100 are 765
The sum of of multiples of 5 less than 100 are 855
The sum of of multiples of 5 less than 100 are 950
where as I only need it to show.
The sum of multiples of 5 less than 100 are 950

[giblit]

then put line 16 outside of the for loop eg line 17 after you move the brace to line 16.

[Tstan]

That was it! thank you!

[keskiverto]

For extra fun, think about http://en.wikipedia.org/wiki/1_%2B_2_%2B_3_%2B_4_%2B_%E2%8B%AF

The multiple is M. The sum equals 1*M + 2*M + .. + n*M == (1+2+..+n)*M.
n*M < 100, so 100/M should get you close to n.