无论我用作输入，输出全为零

Question

This is a question i am working on:

• Prompt the user to enter five numbers, being five people's weights. Store the numbers in a vector of doubles. Output the vector's numbers on one line, each number followed by one space.

• Also output the total weight, by summing the vector's elements.

• Also output the average of the vector's elements.

• Also output the max vector element. So far this is the code i have

   #include <iostream> #include <vector> using namespace std; int main() { const int NEW_WEIGHT = 5; vector<float> inputWeights(NEW_WEIGHT); int i = 0; float sumWeight = 0.0; float AverageWeight = 1.0; int maxWeight = 0; int temp = 0; for (i = 0; i < NEW_WEIGHT; i++){ cout << "Enter weight "<< i+1<< ": "; cout << inputWeights[i]<< endl; cin>> temp; inputWeights.push_back (temp); } cout << "\\nYou entered: "; for (i =0; i < NEW_WEIGHT- 1; i++) { cout << inputWeights.at(i)<< " "; } cout<< inputWeights.at(inputWeights.size() - 1) << endl; for (i =0; i < NEW_WEIGHT; i++){ sumWeight += inputWeights.at(i); } cout <<"Total weight: "<< sumWeight<< endl; AverageWeight = sumWeight / inputWeights.size(); cout <<"Average weight: "<< AverageWeight<< endl; maxWeight= inputWeights.at(0); for (i =0; i < NEW_WEIGHT- 1; i++){ if (inputWeights.at(i) > maxWeight){ maxWeight = inputWeights.at(i); } } cout<< "Max weight: "<< maxWeight << endl; return 0; } 

When i run this code, whatever inputs i use(for the cin>>(...)), i get all zero's as output and i do not know why. can i get some help please.

update cleaned up the code a little by getting rid of the cout<< inputWeights[i]<< endl;
and by adjusting vector inputWeights; at the beginning of the program.But the outputs are still not exactly what they are supposed to be. Instead, only the first 2 inputted values make it as outputs. Any reason why? thanks

update this is the right or correct code. Hope it helps someone in future.

#include <iostream>
#include <vector>

using namespace std;

int main() {
   const int NEW_WEIGHT = 5;
   vector <float> inputWeights;
   int i = 0;
   float sumWeight = 0.0;
   float AverageWeight = 1.0;
   float maxWeight = 0.0;
   float temp = 0.0;

   for (i = 0; i < NEW_WEIGHT; i++){
      cout << "Enter weight "<< i+1<< ": "<< endl;
      cin>> temp;
      inputWeights.push_back (temp);

      }


      cout << "\nYou entered: ";

   for (i =0; i < NEW_WEIGHT- 1; i++){

      cout << inputWeights.at(i)<< " ";
   }
      cout<< inputWeights.at(inputWeights.size() - 1) << endl;

    for (i =0; i < NEW_WEIGHT; i++){

       sumWeight += inputWeights.at(i); 

      }
   cout <<"Total weight: "<< sumWeight<< endl;

       AverageWeight = sumWeight / inputWeights.size();

   cout <<"Average weight: "<< AverageWeight<< endl;

      maxWeight= inputWeights.at(0);
    for (i =0; i < NEW_WEIGHT- 1; i++){
       if (inputWeights.at(i) > maxWeight){
          maxWeight = inputWeights.at(i);
          }
    }

   cout<< "Max weight: "<< maxWeight << endl;

   return 0;
}

Answer 1

You're making a vector of size 5:

const int NEW_WEIGHT = 5;
vector<float> inputWeights(NEW_WEIGHT);

// == 0, 0, 0, 0, 0

Then, in your input loop, you're adding new values to the end:

inputWeights.push_back (42);

// == 0, 0, 0, 0, 0, 42

Then you're outputting the first five elements which were always zero.

You need to choose one thing or the other: either set the size of the vector at the start of the program, or grow the vector with push_back for as long as there's input. Both are valid options.

You can clean up your code and fix the problems by adopting modern C++ (as in, C++11 and later) idiom. You don't need to fill your code with for(int i = 0; i < something; i++) any more. There's a simpler way.

---

// Size fixed in advance:
vector<float> weights(NUM_WEIGHTS);

for (auto& weight : weights) { // note it's `auto&`
  cout << "\nEnter next weight: ";
  cin >> weight; // if it was plain `auto` you'd overwrite a copy of an element of `weight`
}

---

// Size decided by input:
vector<float> weights; // starts empty this time

cout << "Enter weights. Enter negative value to stop." << endl;
float in;
while (cin >> in) {
  if(in < 0) {
    break;
  }
  weights.push_back(in);
}

---

In either case, you can then play with the filled vector using another range-based for :

cout << "You entered: ";
for (const auto& weight : weights) {
  cout << weight << " ";
}

You'll also need to remove the cout << inputWeights[i] << endl; line from your input loop if you resize the vector during input - as written you'd be reading elements which don't exist yet, and will probably get an array-index-out-of-bounds exception.

Answer 2

When you create define your inputWeights you are putting 5 items into it with default values.

vector<float> inputWeights(NEW_WEIGHT);

Change it to be just

vector<float> inputWeights;

And get rid of this line in your code or comment it out

cout << inputWeights[i]<< endl; 

Answer 3

This is what you are looking for from the requirements of your program.

#include <vector>
#include <iostream>

int main() {
    std::vector<double> weights;

    double currentWeight = 0.0;
    const unsigned numberOfWeights = 5;
    std::cout << "Enter " << numberOfWeights << " weights" << std::endl;
    unsigned i = 0;
    for ( ; i < numberOfWeights; ++i ) {
        std::cin >> currentWeight;
        weights.push_back( currentWeight );
    }

    std::cout << "These are the weights that you entered: " << std::endl;
    for ( i = 0; i < weights.size(); ++i ) {
        std::cout << weights[i] << " ";
    }
    std::cout << std::endl;

    double totalWeight = 0.0;
    std::cout << "The total of all weights is: ";
    for ( i = 0; i < weights.size(); ++i ) {
        totalWeight += weights[i];
    }
    std::cout << totalWeight << std::endl;

    std::cout << "The average of all the weights is: " << (totalWeight / numberOfWeights) << std::endl;

    std::cout << "The max weight is: ";
    double max = weights[0];
    for ( i = 0; i < weights.size(); ++i ) {
        if ( weights[i] > max ) {
            max = weights[i];
        }
    }
    std::cout << max << std::endl;

    return 0;
}

The culprit to your problem for seeing all 0s as output is coming from these two lines of code:

const int NEW_WEIGHT = 5;
vector<float> inputWeights(NEW_WEIGHT);

which is the same as doing this:

vector<float> inputWeights{ 0.0f, 0.0f, 0.0f, 0.0f, 0.0f };

you are then looping through up to 5 elements using NEW_WEIGHT when it would be easier to use inputWeights.size() when traversing through containers.

Edit - Condensed Version

#include <vector>
#include <iostream>

int main() {
    std::vector<double> weights;

    double currentWeight           = 0.0;
    const unsigned numberOfWeights = 5;
    unsigned i = 0;

    std::cout << "Enter " << numberOfWeights << " weights" << std::endl;
    for ( ; i < numberOfWeights; ++i ) {
        std::cin >> currentWeight;
        weights.push_back( currentWeight );
    }

    double totalWeight = 0.0;
    double max         = weights[0];
    std::cout << "These are the weights that you entered: " << std::endl;
    for ( i = 0; i < weights.size(); ++i ) {
        std::cout << weights[i] << " ";   // Print Each Weight
        totalWeight += weights[i];        // Sum The Weights

        // Look For Max Weight
        if ( weights[i] > max ) {
            max = weights[i];
        }
    }
    std::cout << std::endl;

    std::cout << "The total of all weights is: " << totalWeight << std::endl;
    std::cout << "The average of all the weights is: " << (totalWeight / numberOfWeights) << std::endl;
    std::cout << "The max weight is: " << max << std::endl;

    return 0;
}