I have to write a program using loops that calculates the sum of all odd numbers between a and b (inclusive), where a and b are inputs.
I made this (below) and it works fine, but I noticed one problem with it: when i enter a larger number followed by a smaller number for the inputs, it returns 0, but when i enter the smaller number first it works perfectly. Any quick fixes for this? :)
import java.util.Scanner;
public class ComputeSumAAndB
{
public static void main (String[] args)
{
Scanner in = new Scanner(System.in);
System.out.print("Please enter 2 integers: "); //prompts user for ints
int a = in.nextInt();
int b = in.nextInt();
int sum = 0;
for (int j = a; j <= b; j++)
{
if (j % 2 == 1)
sum += j;
}
System.out.println("The sum of all odd numbers (inclusive) between " + a + " and "+ b + " is " + sum);
}
}
int temp;
if(a > b) {
temp = a;
a = b;
b = temp;
}
Put this right before your for
loop starts.
The if
checks whether a
(the first number entered) is larger than b
. If it is, it swaps a
and b
. Now your for
loop will always start with the smallest number and iterate up to the larger number (because after this if
, a
will always be the smaller number).
Using this method has the added side effect of making your output make sense. Your output will now always say: "between [smaller number] and [larger number]"
.
rolfl's answer is more elegant and works perfectly fine, but when the user enters the larger number first, your output may look kind of weird: "between [larger number] and [smaller number]"
, etc.
You can get the smaller and larger inputs by using the Math.min() and Math.max functions....
for (int j = Math.min(a,b); j <= Math.max(a,b); j++) {
if (j % 2 == 1) {
sum += j;
}
}
It's not working because A is larger than B in the for loop, you have it iterate while A is less than or equal to B .
You could do what nhgrif says but it's changing your data.. But he is correct.
That's because you are first expecting for the a
input (inferior limit) and then the b
(superior). When your program reaches the for
, j = a
so the condition a <= b
is False, if the first input is larger. In other words it never enters the for
loop.
Actually you should do the following 2 things:
1 It is just just like rolfl mentioned above. You need to put the min and max in the right place in loop.
for (int j = Math.min(a,b); j <= Math.max(a,b); j++) {
if (j % 2 == 1) {
sum += j;
}
}
2 Use if (j % 2 == 1) it is not enough to check whether the num is odd.
eg
a = -5 , b =0; What will be the result?
int sum = 0;
for(int j=-5;j<0;j++)
{
if(j%2 == 1)
{
sum+=j;
}
}
The value for sum will be 0.
We need to change the condition to if(!(j%2 == 0)) Then you will get the expected result.
That's because you are first expecting for the a input (inferior limit) and then the b (superior). When your program reaches the for, j = a so the condition a <= b is False, if the first input is larger. In other words it never enters the for loop.
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