Sum of even numbers and multiplication of odd numbers in a range

Question

Read two numbers being y greater than x, calculate the sum of the numbers pairs of that range of numbers, including the numbers typed; calculate and show the multiplication of the odd numbers of this range, including those typed;

 #include <stdio.h>
 #include <stdlib.h>
 #include <locale.h>
 int main ()
 {
 setlocale(LC_ALL, "PORTUGUESE");
 int X=0, Y=0,somapar=0, cont=0, impar;


printf("Insira o VALOR DE X: ");
scanf("%d", &X);
printf("Insira o VALOR DE Y: ");
scanf("%d", &Y);


if (Y>X)
{

   for (cont=X; cont<=Y; cont++)
{
cont;

 if (cont%2==0)
 {
 somapar = somapar + cont;
  }

  else
  { 
  impar = impar * cont;
   }

}
   }
  else
   {
    printf("X não pode ser maior que Y\n");
     }
    printf("A soma dos números pares nesse intervalo é %d\n", somapar);
    printf("A multiplicação dos números impares nesse intervalo é %d\n", impar);

  system ("pause");
   return 0;
     }

Putting 0 to X and 10 to Y, the output shows only the sum of even numbers that gives 30, but the multiplication gives zero.

Answer 1

Multiplication gives zero because it has not started:

int X=0, Y=0,somapar=0, cont=0, impar;

Once it will multiply it should start the impar with the neutral multiplication value, 1:

int X=0, Y=0,somapar=0, cont=0, impar = 1;

Now it works:

Answer 2

I was almost ready when I had to stop. I’m posting anyway since it has the code running and more organized and simplified.

The main error was not initializing the variable impar with value 1. Two things could happen. To have the value 0 and then any multiplication would give 0. Or to take whatever value was in the memory, which would go very wrong and would seem crazy. In C always initialize variables, unless you know what you’re doing.

#include <stdio.h>

int main() {
    int X = 0, Y = 0, par = 0, impar = 1;
    printf("Insira o VALOR DE X: ");
    scanf("%d", &X);
    printf("Insira o VALOR DE Y: ");
    scanf("%d", &Y);
    if (Y <= X) {
        printf("X não pode ser maior que Y\n");
        return 0;
    }
    for (int cont = X; cont <= Y; cont++) {
        if (cont % 2 == 0) par += cont;
        else impar *= cont;
    }
    printf("A soma dos números pares nesse intervalo é %d\n", par);
    printf("A multiplicação dos números impares nesse intervalo é %d\n", impar);
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.