I want to count int index = 1;. I want it to be added up on each other. For example: 1 + 2 + 3 etc. How can i do this? I've already tried this:
public void countOneToTen() {
int index = 1;
while(index <= 10) {
index = index + index;
}
System.out.println(index);
}
You need to decouple your "sum" variable and your index variable.
Introduce another variable to hold the sum:
public void countOneToTen() {
int sum = 0;
int index = 1;
while (index <= 10) {
sum += index;
index++;
}
System.out.println(sum);
}
Also, use for loops to limit variable scope:
public void countOneToTen() {
int sum = 0;
for (int index = 1; index <= 10; index++) {
sum += index;
}
System.out.println(sum);
}
Your approach didn't work because your index should go from 1 to 10, but the moment you modify it you throw this iteration off course.
Here's what I mean:
index = 1
// index: 1
index = index + index = 2
// index: 2
index = index + index = 4
// We've skipped 3.
// etc.
index = index + index = 8
index = index + index = 16 > 10
1 + 2 + 4 + 8 = 15
Just for fun, here's the Java 8 stream approach:
IntStream.rangeClosed(1, 10).sum();
(thanks to Oleg for pointing out the existence of rangeClosed)
:)
and here's the single-statement approach using the general summation of an arithmetic sequence:
int sum = terms * (min + max) / 2;
Introduce a new variable to store your current sum.
public void countOneToTen() {
int index = 1;
int sum = 0;
while(index <= 10) {
sum += index;
++index;
}
System.out.println(sum);
}
or you could use Gauss' trick. let n = 10 then the sum from 1 to n is n*(n+1)/2
int sum = 0;
for (int i = 0; i <= 10; ++i) {
sum += i;
System.out.println(sum);
}
