Counter that adds 2 in 2

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It is my first post in this forum, I am starting to program, and this question has arisen in an exercise. I have to find the sum of the next 20 numbers to a number entered by keyboard, and the sum of the next 20 even numbers. This is my code: 

if(numero%2==0){
     boolean par=true;
  }else{
     boolean par=false;
  }

  if(par==true){

     for(int i=numero, j=numero+40;i<=j;i+2){   //Este i+2 es lo que tengo mal
        total_par=total_par+i;
     }
  }else{

     for(int i=numero+1,j=numero+40;i<=j;i+2){  //Aquí también
        total_par=total_par+i;
     }
  }

Thanks

    
asked by MigherdCas 01.11.2016 в 14:11
source

4 answers

11

i+2 should be changed to 

i = i + 2

or 

i += 2

Choose the one you prefer.

    
answered by 01.11.2016 / 14:14
source
4

You can also use a formula: 

int total;
if (num % 2 == 0) {
    // k + k + 2 + k + 4 + k + 6 + ... + k + 40
    // k + 20k + 2 + 4 + 6 + ... + 40
    // k + 20k + 20 * (20 + 1)
    // 21k + 420
    total = 21 * num + 420;
} else {
    // k + k + 1 + k + 3 + k + 5 + ... + k + 39
    // k + 20k + 1 + 3 + 5 + ... + 39
    // k + 20k + 20 * 20
    // 21k + 400
    total = 21 * num + 400;
}
System.out.println(total);
  • If num = 1 , then 1 plus the next 20 even numbers is 1 + 2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20 + 22 + 24 + 26 + 28 + 30 + 32 + 34 + 36 + 38 + 40 = 421 .
  • If num = 2 , then 2 plus the next 20 even numbers is 2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20 + 22 + 24 + 26 + 28 + 30 + 32 + 34 + 36 + 38 + 40 + 42 = 462 .
answered by 01.11.2016 в 15:45
2

I would do it this way. Adding one, but reducing the number of steps in half, changing this j=numero+40 for this j=numero+20 .

It would stay like this. 

for(int i=numero, j=numero+20;i<=j;i++)
{
    total_par+=2*i;
}

The if should not exist since it does the same in both cases ... That is, if it is pariiero, and if it is not even, also itero, when it can be said, itero, no matter what happens .

Note: I just realized that the if , yes, should exist, because if it's true, int i=numero , but if it's false, int i=numero+1 .

The next line ... 

for(int i=numero+1,j=numero+40;i<=j;i+2){

It can be corrected in the following way (step by step): 

for(int i=numero+1,j=numero+40;i<=j;i+=2){
for(int i=numero+1,j=numero+40;i<=j;i+=2){
for(int i=numero+0,j=numero+39;i<=j;i+=2){
for(int i=numero+0,j=numero+40;i< j;i+=2){
for(int i=numero+0,j=numero+20;i< j;i+=1){

for(int i=numero,j=numero+20;i<j;i++){
    
answered by 01.11.2016 в 14:56
1

While this is already the answer ... 

private Integer obtenerSuma(Integer intNumero, Integer intCantidadASumar) {
    Boolean intSeed = false;
    Integer  intResultado = 0;

    intSeed = (intNumero % 2)?2:1;

    for(Integer intIndex = 0; intIndex < intCantidadASumar; intIndex + intSeed) {
        intResultado += intNumero;
    }

    return intResultado;
}
    
answered by 10.11.2016 в 14:28
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