FAQ: Conditionals: Lesson - Review

This community-built FAQ covers the “Review” exercise from the lesson “Conditionals: Lesson”.

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Came back now that the full course is released. scanf() is used in the review hint, but was formatting explained anywhere?

2 Likes

I’m thinking the same thing! I could be wrong but i’d swear there is no explanation (or not sufficiently explicit) for the use of scanf() prior to this exercise.

This was a very strange lesson. I don’t remember being introduced to neither the scanf() function nor to the argument “&x”, which the hint suggested. Furthermore it says the lesson is optional, but I couldn’t click “up next” without solving the exercise, which meant I ended up just copying the hint.

1 Like

Same here, follow carefully each previous lessons, scanf() was not approach.

I encounter the same problem with scanf()
I solved it like this, have no idea if it is right

#include <stdio.h>

int main() {

double earth_weight = 50;
printf(“Earth weight: %f kg\n”, earth_weight);
int numberPlanet = 3;

float mercury1 = earth_weight0.38;
float venus2 = earth_weight
0.91;
float mars3 = earth_weight0.38;
float jupiter4 = earth_weight
2.34;
float saturn5 = earth_weight1.06;
float uranus6 = earth_weight
0.92;
float neptune7 = earth_weight*1.19;

{
if (numberPlanet = 1){
printf(“Mercury: %f\n”, mercury1);
}
else if (numberPlanet = 2){
printf(“Venus: %f\n”, venus2);
}
else if (numberPlanet = 3){
printf(“Mars: %f\n”, mars3);
}
else if (numberPlanet = 4){
printf(“Jupiter: %f\n”, jupiter4);
}
else if (numberPlanet = 5){
printf(“Saturn: %f\n”, saturn5);
}
else if (numberPlanet = 6){
printf(“Uranus: %f\n”, uranus6);
}
else if (numberPlanet = 7) {
printf(“Neptune: %f\n”, neptune7);
}
}

}

This is what I came up with. Not that pleased with its readability but seems to be working. Hope it helps.

#include <stdio.h>

int main() {

float earthWeight;
int planetNumber;
float currentWeight;

printf(“What is your weight on Earth?\n”);
scanf("%f", &earthWeight);

printf(“Enter the number of the planet you want to compete in:\n1 - Mercury\n2 - Venus\n3 - Mars\n4 - Jupiter\n5 - Saturn\n6 - Uranus\n7 - Neptune\n”);
scanf("%i", &planetNumber);
switch(planetNumber) {
case 1:
currentWeight = earthWeight * 0.38;
break;
case 2:
currentWeight = earthWeight * 0.91;
break;
case 3:
currentWeight = earthWeight * 0.38;
break;
case 4:
currentWeight = earthWeight * 2.34;
break;
case 5:
currentWeight = earthWeight * 1.06;
break;
case 6:
currentWeight = earthWeight * 0.92;
break;
case 7:
currentWeight = earthWeight * 1.19;
break;
default:
printf(“Unknown Planet:\n”);
break;
}

printf(“Your current weight is: %f\n”, currentWeight);
}

You don’t need currentWeight because you don’t need to save earthWeight, just use earthWeight = eatrhWeight * planet weight.
Also, you can printf weight inside switch case for example for case 7 :

case 7:
printf(“Your current weight on Neptune is: %f\n”, earthWeight * 1.19);
break;

It’s ok, but you don’t need to type weight for every planet. Just make variable weight and multiply it with planet constant.
For example :
if (numberPlanet = 1){
printf(“Mercury: %f\n”, weight0.38);
}
else if (numberPlanet = 2){
printf(“Venus: %f\n”, weight
0.91);
}
etc.

1 Like

I don’t know why you don’t include return value at the end of the function because main function is int ?
Here is my solution :

#include <stdio.h>

int main() {
double weight;
int planet;
printf(“Enter the weight: “);
scanf(”%lf”,&weight);
printf(“Enter the planet from 1-7: “);
scanf(”%d”,&planet);

switch (planet) {
case 1:
printf(“Your weight on Mercury is %.2lf\n”,weight0.38);
break;
case 2:
printf(“Your weight on Venus is %.2lf\n”,weight
0.91);
break;
case 3:
printf(“Your weight on Mars is %.2lf\n”,weight0.38);
break;
case 4:
printf(“Your weight on Jupiter is %.2lf\n”,weight
2.34);
break;
case 5:
printf(“Your weight on Saturn is %.2lf\n”,weight1.06);
break;
case 6:
printf(“Your weight on Uranus is %.2lf\n”,weight
0.92);
break;
case 7:
printf(“Your weight on Neptune is %.2lf\n”,weight*1.19);
break;
default:
printf(“Unknown planet\n”);
break;
}
return 0;
}

As the others mentioned, this task is impossible for an inexperienced programmer without using the hints, because scanf() and the & operator are never explained. Fortunately I’m fairly experienced with C so I thought I might try to explain things a little.
The solution for this exercise looks something like this:

#include <stdio.h>

int main() {
  float weight = 0;
  int planet = 0;

  printf("What is your Earth weight?\n> ");
  scanf("%f", &weight);

  printf("Which planet would you like to fight on?\n> ");
  scanf("%d", &planet);

  switch(planet) {
    case 1:
      weight *= 0.38;
      break;
    case 2:
      weight *= 0.91;
      break;
    case 3:
      weight *= 0.38;
      break;
    case 4:
      weight *= 2.34;
      break;
    case 5:
      weight *= 1.06;
      break;
    case 6:
      weight *= 0.92;
      break;
    case 7:
      weight *= 1.19;
      break;
    default:
      printf("Error: Invalid planet supplied.\n");
  }
  printf("Interplanetary weight: %f\n", weight);
}

The important parts of the code are lines 7-11. This is how you use the aforementioned scanf() function. It takes the general form scanf("<format string>", &<variable>). As we can see, the function takes two parameters.

The first parameter is what’s called a format string. It is a placeholder which includes a format specifier. We learned about these placeholders previously in the Variables lesson, but it was used in printf() rather than scanf(). The placeholder %f lets the compiler know that you’re reading in a floating-point (decimal) number, whereas %d lets the compiler know you’re reading in an integer (%i would signify the same thing).

The second parameter can be thought of as the variable you’re putting the input into. The & operator does have a specific effect here, but it’s tied to a more advanced topic called pointers. For now, just remember that this second parameter is just the name of the variable with & in front of it (for the curious: & retrieves the memory address of the variable as opposed to the number that is currently stored in the variable).

I hope this helps y’all understand a little bit better how to get user input. I don’t know why they introduced it here with no prior mention. I guess they wanted people to research stuff on their own, but in my experience it just demotivates me when I think I understood everything in a lesson and they throw something new at me. It makes me feel like I missed something when really I didn’t at all.

Don’t lose your drive to learn because of this. C is a difficult language to learn, but that just makes it all the more rewarding when your code compiles.

2 Likes

Thank you very much for explaining this and demonstrating its use in code!

How might we use a place-holder for a string? %s ?

This works elegantly when I also include the choice of planets.