#include <stdio.h>

int calculate(int n1,int n2);
int read_num();

int main(){
    int num1,num2,sum;
    
    test(calculate(1, 10) == 30, "test1");
    test(calculate(2, 4) == 6, "test2");

    num1 = read_num();
    num2 = read_num();
    sum  = calculate(num1,num2);
    printf("Answer: %d",sum);
    
    return 0;
}

int read_num() {
    int i;

    printf("Please enter any number: ");
    scanf("%d",&i);
    return(i);
}

void test(int v, char* msg) {
    if (!v) {
        printf("error: ");
        puts(msg);
    }
}

int calculate(int n1,int n2){
    int summ=0;
    while(n1 <= n2){
        if(n1 % 2 == 0) {
            summ += n1;
        }
        n1++;
    }
    return summ;
}