FAQ: Conditionals & Logic - Review

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I did the optional exercise for the review section.
I used a switch statement to calculate the weight on different planets, as seen below(and it works). However when I want to add the statement "your weight in this planet is " std::cout << "Your weight in this planet is " +(weight * rg2); I get an error.
The error is: "invalid operand of char + binary operator
Why is that?:thinking:

int main() {
  double weight;
  std::cout << "What is your earth weight\n";
  std::cin >> weight;
  int planet;
  std::cout << "Enter number (1-6) for planet to fight on\n";
  std::cin >> planet;
  switch (planet){
    case 1:
      {double rg1 = 0.78;
      std::cout << (weight * rg1);}
      break;
    case 2:
      {double rg2 = 0.39;
      std::cout << (weight * rg2);}
      break;
    case 3:
      {double rg3 = 2.65;
      std::cout << (weight * rg3);}
      break;
    case 4:
      {double rg4 = 1.17;
      std::cout << (weight * rg4);}
      break;
    case 5:
      {double rg5 = 1.05;
      std::cout << (weight * rg5);}
      break;
     case 6:
      {double rg6 = 1.23;
      std::cout << (weight *rg6);}
      break;
  }

Solved
I got it!!!
I was concatenating using “+” instead of " <<" for the standard output!!!
Now my output is how I wanted it “your weight on this planet is ***”

It took me way longer than it should have to figure out why declaring a string failed when compiling…
Strings were mentioned in the earlier lessons, but no examples or details on how to use them were given.
After some googling I found out you have to have “using namespace std;” or use std::string instead of just string when declaring.

Once I finally figured that out, this was my final program.

#include <iostream>
using namespace std;

int main() {
 
  double earthWeight;
  int planetNumber;
  double planetWeight;
  string planetName;
  
  std::cout << "Please enter your weight on Earth: ";
  std::cin >> earthWeight;
  
  std::cout << "Please select a planet from the following list:\n\n";
  
  std::cout << "   1: Venus\n";
  std::cout << "   2: Mars\n";
  std::cout << "   3: Jupiter\n";
  std::cout << "   4: Saturn\n";
  std::cout << "   5: Uranus\n";
  std::cout << "   6: Neptune\n\n";
  
  std::cout << "Planet Number: "; 
  std::cin >> planetNumber;  
  
  switch (planetNumber){
    case 1 :
      planetWeight = earthWeight * 0.78;
      planetName = "Venus";
      break;
    case 2 :
      planetWeight = earthWeight * 0.39;
      planetName = "Mars";
      break;
    case 3 :
      planetWeight = earthWeight * 2.65;
      planetName = "Jupiter";
      break;
    case 4 :
      planetWeight = earthWeight * 1.17;
      planetName = "Saturn";
      break;
    case 5 :
      planetWeight = earthWeight * 1.05;
      planetName = "Uranus";
      break;
    case 6 :
      planetWeight = earthWeight * 1.23;
      planetName = "Neptune";
      break;
    default :
      planetName = "Unknown";
      break;
  }
  
  if (planetName == "Unknown"){
    std::cout << "Invalid planet input.\n";
  }else{
    std::cout << "Your weight on " << planetName << " would be " << planetWeight << "\n";
  }
  
}
3 Likes

//My final program

#include

int main() {
double w = 150;
int p = 8;
std::cout << “What is your earth weight?\n”;
std::cin >> w;
std::cout << “Which plant number will you fight on?\n”;
std::cout << “1. Venus 2. Mars 3. Jupiter 4. Saturn 5. Uranus 6. Neptune \n\n”;
std::cin >> p;

switch § {
case 1 :
std::cout << "Your weight is "<< w0.78 <<“lbs,\n”;
break;
case 2 :
std::cout << "Your weight is " << w
0.39 <<“lbs,\n”;
break;
case 3 :
std::cout << "Your weight is " << w2.65 <<“lbs,\n”;
break;
case 4 :
std::cout << "Your weight is "<< w
1.17 <<“lbs,\n”;
break;
default :
std::cout << "Your weight is "<< w*1.05 <<“lbs,\n”;
break;
}

}

Here’s my solution to the exercise! :smiley: it works

#include

int main() {
double weight;
std::cout << “Enter your earth weight\n”;
std::cin >> weight;

int planet;
std::cout << “Please, choose a number for the planet you want to fight on\n”;
std::cout << " 1 = Venus\n";
std::cout << " 2 = Mars\n";
std::cout << " 3 = Jupiter\n";
std::cout << " 4 = Saturn\n";
std::cout << " 5 = Uranus\n";
std::cout << " 6 = Neptune\n";
std::cin >> planet;
double v1=0.78;
double m2=0.39;
double j3=2.65;
double s4=1.17;
double u5=1.05;
double n6=1.23;

switch (planet) {
case 1:
std::cout << "Your weight in Venus is " << (weightv1) <<"\n";
break;
case 2:
std::cout << "Your weight in Mars is " << (weight
m2) << “\n”;
break;
case 3:
std::cout << "your weight in Jupiter is " << (weightj3) << “\n”;
break;
case 4:
std::cout << “Your weight in Saturn is” << (weight
s4) << “\n”;
break;
case 5:
std::cout << “Your weight in Uranus is” << (weightu5) << “\n”;
break;
case 6:
std::cout << “Your weight in Neptune is” << (weight
n6) << “\n”;
break;
default:
std::cout << “Error in numbers\n”;

  }

}

Here’s mine pretty much as those who choose a similar switch-case solution. Have a good one!

#include
#include <stdlib.h>

int main() {
double weight;
int planet;
std::cout << “Hi champ! what’s your weight in Earth?\n”;
std::cin >> weight;
std::cout << “On which planet is your next fight?\n 1)Venus 2)Mars 3)Jupiter\n 4)Saturn 5)Uranus 6)Neptune\n”;
std::cin >> planet;
// I choose to have a more clean structure with a switch-case flow instead of the if-else if-else
// (which is completely right as an option)
switch(planet) {
case 1: weight = weight / 0.78; std::cout << “Your weight in Venus is:\n” << weight << " kg\n";
break;
case 2: weight = weight / 0.39; std::cout << “Your weight in Mars is:\n” << weight << " kg\n";
break;
case 3: weight = weight * 2.65; std::cout << “Your weight in Jupiter is:\n” << weight << " kg\n";
break;
case 4: weight = weight * 1.17; std::cout << “Your weight in Saturn is:\n” << weight << " kg\n";
break;
case 5: weight = weight * 1.05; std::cout << “Your weight in Uranus is:\n” << weight << " kg\n";
break;
case 6: weight = weight * 1.23; std::cout << “Your weight in Neptune is:\n” << weight << " kg\n";
break;
}
}

This is what I used:

#include <iostream>
#include <thread>
#include <chrono>

int main() {
int weight;
int planet;
std::cout << "what is your earth weight? ";
std::cin >> weight;
std::cout << "which planet do you want to fight in? ";
std::cin >> planet;
switch (planet) {
  case 1:
std::cout << planet / 0.78 << std::endl;
    break;
  case 2:
std::cout << planet / 0.39 << std::endl;
    break;
  case 3:
std::cout << planet / 2.65<< std::endl;
    break;
  case 4:
std::cout << planet / 1.17 << std::endl;
    break;
  case 5:
std::cout << planet / 1.05 << std::endl;
    break;
  case 6:
std::cout << planet / 1.23 << std::endl;
    break;
  default:
    std::cout << "Invalid\n";
    break;
  
}

}```
also please make sure to tell us what arithmetic to use :D

Guys,why the he** is no (return 0;) needed at the end?!
Cheers for the replies!

Tried to do a fancy work… but I failed…
Here is my code:
#include

int main() {
double EW;
int num;
cart PN;
double FW;
wait
//Variables I defined
std::cout << “Hello warrior!\n”;
std::cout << “This is a programme to help you with calculate the weight of you in different planet only if you answer the following question.\n”;
//Greatings and intros.
std::cout << “1.What is your weight on EARTH?\n”;
std::cin >> EW;
if (EW <= 0){
std::cout >> “Please renter your weight.\n”;
return;
//In case someone enter a impossible number of weight.
} else {
std::cout >> “Great!”;
}
std::cout << “2.Which planet you want to fight on? Please enter the number of the planet. Here is the number of each planet:\n\n”;
std::cout << " 1. Venus 2. Mars 3. Jupiter\n";
std::cout << " 4. Saturn 5. Uranus 6. Neptune\n\n";
//A tip.
std::cin >> num;
//Enter the number of planet.
switch (num) {
case 1:
FW == EW* 0.78;
PN == “Venus”;
case 2:
FW == EW* 0.39;
PN == “Mars”;
case 3:
FW == EW* 2.56;
PM == “Jupiter”;
case 4:
FW == EW* 1.17;
PN == “Saturn”;
case 5:
FW == EW* 1.05;
PN == “Uranus”;
case 6:
FW == EW* 1.23;
PN == “Neptune”;
default:
std::cout << “We only know about thouse 6 planets right now.”;
return;
//In case user enter a number which is not 1, 2, 3, 4, 5, or 6.
}
std::cout << “So your wight on”;
std::cout >> PN;
std::cout << “is:”;
std::cout >> FW;
std::cout << “\n THX for using this programme!GH & HF!”;
//Final statement
}
I would appreciate if someone can help me!

Compiled and executed using
g++ space.cpp
./a.out
And typed the following code, however the code didn’t run and code academy let me pass?
Any help would be greatly appreciated:

int main() {
double eweight;
std::cout <<“What is your earth weight?\n”;
std::cout <<"My earth weight is ";
std::cin >> eweight;

int num;
std::cout <<“What number planet do you want to fight on?\n”;
/*#, Planet, Relative gravity
1 Venus 0.78
2 Mars 0.39
3 Jupiter 2.65
4 Saturn 1.17
5 Uranus 1.05
6 Neptue 1.23
*/
std::cin >> num;
double pweight;
switch(num){
case 1:
pweight=eweight * 0.78;
break;
case 2:
pweight=eweight * 0.39;
break;
case 3:
pweight=eweight * 2.65;
break;
case 4:
pweight=eweight * 1.17;
break;
case 5:
pweight=eweight * 1.05;
break;
case 6:
pweight=eweight * 1.23;
break;
default:
std::cout <<“Invalid number please try again\n”;
}
std::cout <<“Your planet weight is “<<pweight<<”\n”;

}

Since the main function is a interger(int). Therefore you must return a interger. So imagine if the main function was a string (int main > string main). You have to return a string like

return "hello"

or if it was a bool function (int main > bool main). Then the return would be either true or false

return true

cheers mate!!
have still a lot to cover :confused:

I don’t know why it’s have a lot of “\n” in your HINT
Can you explain to me why is it?
Thanks a lot :smile:\

Here is my solution. I decided to use a switch as well - seems like less work?

#include <iostream>

int main() {
  int earth_weight;
  int planet;
  double planetary_weight;
    
  std::cout << "Enter your earth weight: \n";
  std::cin >> earth_weight;
  
  std::cout << "I have information on the following planets: \n";
  std::cout << "1.Venus 2.Mars 3.Jupiter \n";
  std::cout << "4.Saturn 5.Uranus 6.Neptune \n";
  std::cout << "Please make your selection: \n";
  std::cin >> planet; 
  
  switch (planet) {
    case 1:
      std::cout << "Venus\n";
      planetary_weight = earth_weight * .78;
        break;
    case 2:
      std::cout << "Mars\n";
      planetary_weight = earth_weight * .39;
        break;
    case 3:
      std::cout << "Jupiter\n";
      planetary_weight = earth_weight * 2.65;
        break;
    case 4:
      std::cout << "Saturn\n";
      planetary_weight = earth_weight * 1.17;
        break;
     case 5:
      std::cout << "Uranus\n";
      planetary_weight = earth_weight * 1.05;
        break;
      case 6:
      std::cout << "Neptune\n";
      planetary_weight = earth_weight * 1.23;
        break;
      default: 
      std::cout << "Invalid input\n";
  }
  
  std::cout << "Your weight on this planet is " << planetary_weight << "\n";
}
1 Like

I assumed that he already knew what planet was which based off the number. This is what i did

#include <iostream>
using namespace std;
// W = M x G
int main() {
  
  float earth_weight, mass, gravity, weight;
  short planet;
  
  cout<<"What is your earth weight?\n";
  cin>> earth_weight;
  
  cout<<"Enter the number of the planet that you are fighting in? \n";
  cin>>planet;
  //calculating his mass from his earth weight
  mass = earth_weight/0.98;
  //calculating his weight on the planet he inputed
  switch(planet){
    case 1 :
      weight = mass * 0.78;
      break;
    case 2:
      weight = mass * 0.39;
      break;
    case 3:
      weight = mass * 2.65;
      break;
    case 4:
      weight = mass * 1.17;
      break;
    case 5:
      weight = mass * 1.05;
      break;
    case 6:
      weight = mass * 1.23;
      break;
  }
  cout<<"Your weight on planet #"<<planet<<"is "<<weight<<endl;
   
}

Hi Netpro,
Thanks for sharing your work! Looks neat.

Yeah, I encountered the same problem previously, and learnt that “string” is not a variable that is really at the bottom of the heart of C++ like char, int, double, etc. Rather, string is within std, the standard library, thus it is necessary to add the “std::” bit. I read it’s because string is essentially a ‘string’ of characters (chars).

Anyway just wanted to add few words from my recent learning as well. Happy coding.

Hi all,

Here is my piece of work. I made an extra effort to deal with naughty users, who will put in negative values as weight, etc. haha.
This can also be found from: https://github.com/haratzj/space/blob/master/space.cpp.

Cheers, Happy coding.

//This is an app that converts one's earth weight to a chosen planet weight

#include <iostream>

int main (){
    int planet_num, whilecheck=0, ifcheck=0;
    double earth_weight, venus=0.78, mars=0.39, jupiter=2.65, saturn=1.17, uranus=1.05, neptune=1.23;
    std::cout << "What is your weight on Earth?: ";
    std::cin >> earth_weight;

    // This while loop checks the earth_weight input and make sure its not negative. Giving 5 chances.
    while (earth_weight < 0 && whilecheck < 5) {
        std::cout << "You can't have negative value here. Please re-enter your weight : ";
        std::cin >> earth_weight;
        whilecheck = whilecheck +1;
    }
    // If the user has put in a negative value for more than 5 times, the code is forced to break, by returning 0.
    if (whilecheck > 4) {
        std::cout << "Stop putting in negatvie number!\n";
        return 0;
    }
    std::cout << "Also, on what planet do you want to fight?\n" << "1-Venus, 2-Mars, 3-Jupiter, 4-Saturn, 5-Uranus, 6-Neptune: ";
    std::cin >> planet_num;

    // Similar input validity check
    while (planet_num != 1 && planet_num != 2 && planet_num != 3 && planet_num != 4 && planet_num != 5 && planet_num !=6 && ifcheck < 5) {
        std::cout << "Please choose a valid option : ";
        std::cin >> planet_num;
        ifcheck = ifcheck +1;
    }
    if (whilecheck > 4 || ifcheck >4) {
        std::cout << "Stop putting in invalid inputs!\n";
        return 0;
    }

    switch(planet_num){
        case 1:
        std::cout << "You have chosen Venus! " << "You will weigh " << earth_weight*venus << "kg there!\n";
        break;
        case 2:
        std::cout << "You have chosen Mars! " << "You will weigh " << earth_weight*mars << "kg there!\n";
        break;
        case 3:
        std::cout << "You have chosen Jupiter! " << "You will weigh " << earth_weight*jupiter << "kg there!\n";
        break;
        case 4:
        std::cout << "You have chosen Saturn! " << "You will weigh " << earth_weight*saturn << "kg there!\n";
        break;
        case 5:
        std::cout << "You have chosen Uranus! " << "You will weigh " << earth_weight*uranus << "kg there!\n";
        break;
        case 6:
        std::cout << "You have chosen Neptune! " << "You will weigh " << earth_weight*neptune << "kg there!\n";
        break;
        default: //default does not have 'break' as it really doesn't matter. but it may be a good practise to include one?
        std::cout << "Sorry, something went wrong... Stay on the Earth maybe...\n";
    }
}

I added on to this.

#include <algorithm>
#include <locale>
#include <iostream>

using namespace std;

int main() {
  //It should ask him what his earth weight is.
  cout << "How much do you weigh on Earth?\n";
  double weight;
  cin >> weight;
  
  //Ask him to enter a the planet he wants to fight on.
  string planet;
  cout << "Which planet do you want to fight on?\n";
  cin >> planet;
  
  // convert string to back to lower case
  for_each(planet.begin(), planet.end(), [](char & c) {
	  c = tolower(c);
  });  
  
  //It should then compute his weight on the destination planet.
    if (planet == "venus")
      weight *= 0.78;
    else if (planet == "mars")
      weight *= 0.39;
    else if (planet == "jupiter")
      weight *= 2.65;
    else if (planet == "saturn") 
      weight *= 1.17;
    else 
      cout << "Planet unknown.\n";
  
  cout << "Your weight will be " << weight << ".\n";
}

I struggled a little at the start with the switch, so i copied my code into a notebook and tried re-writing with if statements. Which did work, but i was determined not to move on in the lessons until i figured what i was doing wrong with the switch statements, in the end it was me putting the wrong variables into the switch statements… so here’s the final code i did, and it works! :slight_smile:

#include <iostream>

int main() {
  
  double earth;
  int planet;
  
  std::cout << "Please enter your earth weight: ";
  std::cin >> earth;

  std::cout << "Please Chose Your Planet You Want To Visit!\n";
  std::cout << "1.Venus 2.Mars 3.Jupiter 4.Saturn 5.Uranus 6.Neptune\n";
  std::cin >> planet;
  
  switch (planet) {
    case 1:
      earth = planet * 0.78;
      break;
    case 2:
      earth = planet * 0.39;
      break;
    case 3:
      earth = planet * 2.65;
      break;
    case 4:
      earth = planet * 1.17;
      break;
    case 5:
      earth = planet * 1.05;
      break;
    case 6:
      earth = planet * 1.23;
      break;
    default:
      std::cout << "Invalid\n";
      break;
      
  }
  
  std::cout << "Your weight will be: " << earth << "\n";
  
  
  
  
  
  
  
  
  
}