CODEWITHSUNDEEP
java
Luis Ort
Luis Ort

Reputation: 41

Need assistance on for loop example, I don't know how it works

Can anyone help me understand how this equals to 400? I can't figure it out how the for works.

import java.util.*; //for class Scanner
public class Exercise 
{
   public static void main(String[] args) {
   Scanner reader = new Scanner(System.in);

   int value =0;
   for (int num = 10; num<= 40; num +=2){
       value =value+num;
   }
   System.out.println(value); 
}

Upvotes: 2

Views: 71

Answers (3)

Robby Cornelissen
Robby Cornelissen

Reputation: 97212

It's probably easiest to understand if you look at the actual values that will be used when the loop is evaluated. Given that num is initialized to 10, and the loop will end when it equals or exceeds 40, these are the 16 iterations the loop goes through:

value = value + num
-------------------
value = 0     + 10
value = 10    + 12
value = 22    + 14
value = 36    + 16
value = 52    + 18
value = 70    + 20
value = 90    + 22
value = 112   + 24
value = 136   + 26
value = 162   + 28
value = 190   + 30
value = 220   + 32
value = 252   + 34
value = 286   + 36
value = 322   + 38
value = 360   + 40

The final value of value being 400.

Upvotes: 6

Todd Matthews
Todd Matthews

Reputation: 291

first pass

value = value + num;
  10   =   0 +    10;

second pass:

value = value + num;
 22  =  10   +     12

third pass:

 value = value + num;
  36         22  +  14

in a for loop

for(initializer, condition, increment){

   do something!

}

initializer is the beginning number

condition is what will cause the loop to stop

increment is how much you want to add to the initializer in order to meet the condition at the correct time.

Upvotes: 1

Elliott Frisch
Elliott Frisch

Reputation: 201467

A Java for loop is an example of a Traditional for loop, from the linked Wikipedia page,

for(INITIALIZATION; CONDITION; INCREMENT/DECREMENT){
  // Code for the for loop's body
  // goes here.
}

So, your posted example is equivalent to

int value = 0;
int num = 10;
while (num <= 40) {
  value += num;
  num += 2;
}
System.out.println(value);

Of course, you could simply add output to see it in action with,

for (int num = 10; num <= 40; num += 2) {
    System.out.printf("value = %d, num = %d%n", value, num);
    value = value + num;
}

Upvotes: 5

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