Ratings from 0 to 100

In this case, what is most recommended when verifying a condition with multiple options, is always to evaluate at the beginning the specific cases (0 and 100) and at the end those that would encompass a range. (greater than or equal to 70 || less than 70).

if ( calif == 0 ){
    //Repite Curso
} else if ( calif == 100 ) {
    //Obtiene Beca
} else if ( calif < 70 ) {
    //Reprobado
} else 
    //Aprobado ( ya que no se cumplio ninguna condicion anterior, es muy
    //buena practica de programacion siempre poner los casos especificos al comienzo)

Greetings, I hope you serve

The error occurs to you because the case of 100 is never checked since, when fulfilling the second condition >= 70 , it executes that block and does not check more conditions since it was chained with if-else .

I suppose that the messages of Repite curso and Alumno con beca you want to show in addition to the messages of Aprobado or Reprobado . That is, in addition to showing the student's approved message, if you also get a scholarship, show that you have obtained it. And if the student is failing, if he also repeats a course, that shows both.

The code would look like this:

#include <iostream>
using namespace std;

int main(void)
{
    int calif;

    /*
    si es mayor o igual a 70, esta aprobado
    si es menor a 70 esta reprobado
    si saca 0 debe repetir curso
    si saca 100 obtiene una beca
    */

    cout << "\n\tLISTADO DE CALIFICACIONES";
    cout << "\n Ingrese la calificacion:  ";
    cin >> calif;

    if (calif < 0 || calif > 100) {
        cout << "ERROR: Dato introducido fuera de rango (0-100).\n";
        return -1;
    }

    if (calif >= 70)
    {
        cout << "Alumno Aprobado, FELICIDADES.\n";   

        if (calif == 100) {
            cout << "Alumno con BECA.\n";
        }
    }
    else 
    {
        cout << "Alumno Reprobado, LO SIENTO.\n";

        if (calif == 0) {
            cout << "Repite curso.\n";
        }
    }

    return 0;
}

Update : add the range of data entered in the code.

Let's play a game.

We will play that I am your program and you have entered 100 within calif .

We started.

I interpret if(calif==0) , I know that calif is 100 so the question is:

  

Is one hundred zero?

Obviously not, so I get into the branch else of which hangs another if .

I interpret if(calif>=70) , I know that calif is 100 so the question is:

  

Is one hundred more or equal to seventy?

Hey, yes! I enter the branch of if and I find that I have to show something on the screen, so I tell you:

Alumno Aprobado, FELICIDADES

Since I have entered the if , I will not execute else , so I'm going to the end of this branch of conditions and I find return 0 ;

Interpretation return 0 , the program ends.

Possible solution:

You can check that the number is exactly in a range instead of checking only one of the limits:

if (calif == 0)
{
    cout<<"Repite curso";
}
else if (calif < 70 && !(calif <= 0))
{
    cout<<"Alumno Reprobado, LO SIENTO";
}
else if (calif < 100 && !(calif <= 70))
{
    cout<<"Alumno Aprobado, FELICIDADES";   
}
else if(calif == 100)
{
    cout<<"Alumno con BECA";
}

The easiest thing is to do the checks in a strict ascending or descending order. Why?

Because in a chain if - else , in else we can discard everything that has already been evaluated in if .

Example with ascending order

if (calif == 0)
{
    // repite curso
}
else if (calif < 70) // si llegamos aqui, calif != 0
{
    // reprobado
}
else if (calif < 100) // si llegamos aqui, calif >= 70
{
    // aprobado  
}
else // si llegamos aqui, calif >= 100
{
    // beca
}

Example with decentent order

if (calif == 100)
{
    // beca
}
else if (calif >= 70) // si llegamos aqui, calif != 100
{
    // aprobado
}
else if (calif > 0) // si llegamos aqui, calif < 70
{
    // reprobado
}
else // si llegamos aqui, calif <= 0
{
    // repite curso
}