CODEWITHSUNDEEP
c++
b_dobres
b_dobres

Reputation: 43

Strange behavior when finding range of values between two numbers

I've recently started working through the "c++ primer 5th Edition". I'm currently on the following exercise:

Exercise 1.11: Write a program that prompts the user for two integers. Print each number in the range specified by those two integers.

I have written the following code as a solution :

#include <iostream>

int main(){
    int num1 = 0, num2 = 0;
    std::cout << std::endl << "Please enter two numbers to find a range between" << std::endl;
    std::cin >> num1 >> num2; 


    if (num1 < num2)
        while (num1 <= num2){
            std::cout << std::endl << num1;
            ++num1;
        }

    if (num2 < num1)
        while (num2 <= num1){
            std::cout << std::endl << num2;
            ++num2;
        }

    if (num1 == num2)
        std::cout << std::endl << num1;

    std::cout << std::endl;

However when I input the numbers, the output is not quite correct;

Sample input:

Please enter two numbers to find a range betweem
>> 1 5

Sample output:

1
2
3
4
5
5
6

What I don't understand, is that if the first number i input is larger than the first (e.g. num1 > num2), then the program produces the desired result, eg:

Please enter two numbers to find a range between
>> 5 1


1
2
3
4
5

What is particularly confusing is that, when I swap the order of the conditional statements, the first example will work correctly and the second will produce incorrect output.

Just to be clear, I'm aware of a cleaner, correct solution to this exercise. I would just like to know the reason that my program functions this way.

I'd very much appreciate an explanation!

Upvotes: 4

Views: 138

Answers (3)

Rohan Sampson
Rohan Sampson

Reputation: 71

As Technoid said, add else statements. Your code should now become:

#include <iostream>

int main(){
    int num1 = 0, num2 = 0;
    std::cout << std::endl << "Please enter two numbers to find a range between" << std::endl;
    std::cin >> num1 >> num2; 


    if (num1 < num2)
        while (num1 <= num2){
            std::cout << std::endl << num1;
            ++num1;
        }

    else if (num2 < num1)
        while (num2 <= num1){
            std::cout << std::endl << num2;
            ++num2;
        }

    else if (num1 == num2)
        std::cout << std::endl << num1;

    /* Alternatively for (num1 ==num2) use:

    else
        std::cout << std::endl << num1;     

    */

    std::cout << std::endl;
}

Upvotes: 1

SSH
SSH

Reputation: 1627

Actually you are increamenting your num1 in the first condition when all iterations of while loop completed your second if condition gets true because its the loop exit condition of first if(i.e. num1 <= num2), so your second if triggered and print the last 5 6 .

While in second case your first if not triggered and you reach the second if and hence your flow works properly

Upvotes: 1

Technoid
Technoid

Reputation: 435

Its so simple. Just add 'else' for the bottom two if loops Basically you need to go through only 1 'if' loop, but your program goes through each 'if' loop

Upvotes: 6

Related Questions