我的for循环后的代码无法正常工作，for循环后的print语句无法打印

Question

My code does not continue after the for loop, the cursor just remains there blinking. I tried it on multiple compilers still same problem.

   Input:
   3 50
   60 20
   100 50
   120 30

when I give this input it take 3 values, than does not print the statement after the for loop. It just pauses. :(

here is the for loop (image)

This is the problem I face. not working after taking input (image)

Here is my code.

#include <iostream>
#include <vector>
#include <algorithm>

using std::vector;

double get_optimal_value (int capacity, vector<int> weights, 
                              vector<int> values, int n){
    std::cout<<"we are in the function";
    double value = 0.0;
    int current_weight = 0;

    vector<double> v_by_w(n);
    for (int i = 0; i < n; ++i)
        v_by_w[i] = values[i] / weights[i];

    std::cout<<"printing the v/w elements";
    for (int i = 0; i < n; ++i)
        std::cout<< v_by_w[i] << " ";

    while( current_weight < capacity ) {
        int maxi = std::max_element(v_by_w.begin(),v_by_w.end()) - 
        v_by_w.begin();

        if((capacity - current_weight) > weights[maxi]){
            current_weight += weights[maxi];
            value = values[maxi];
        } else
            value += v_by_w[maxi]*(capacity - current_weight);

        v_by_w[maxi] = -1;
    }

    return value;
}

int main() {
    int n;
    int capacity;
    char ch;
    std::cin >> n >> capacity;
    vector<int> values(n);
    vector<int> weights(n);
    for (int i = 0; i < n; i++) {
        std::cout<<"hello "<<i ;
        std::cin >> values[i] >> weights[i];
    }

    std::cout<<"we took the values"; //why won't this print?

    double optimal_value = get_optimal_value(capacity, weights, values, n);

    std::cout.precision(10);
    std::cout << optimal_value << std::endl;

    return 0;
}

My goal is to print that we took the input after taking the input.

please let me know why does this happen. What can I do to prevent it.

This will really help me :)

Answer 1

I tried running your code below:

int main()
{
int n;
int capacity;
char ch;
std::cin >> n >> capacity;
vector<int> values(n);
vector<int> weights(n);
for (int i = 0; i < n; i++) {
    std::cout<<"hello "<<i ;
    std::cin >> values[i] >> weights[i];
}

std::cout<<"we took the values"; //this is getting printed after taking 2n input from keyboard
}

Below is a explanation of sample run of your program:

On running the code, I get empty console window. At this point, the line below is expecting two input from the keyboard: std::cin >> n >> capacity; So I give the below input(2 space 3 enter) 2 3 // please note with this input 2 is assigned to variable n and 3 is assigned to variable capacity

Now the program execution control enters your for-loop and print the line below code: std::cout<<"hello "<

output hello 0 Now enter your two input:output hello 011 12 (11 space 12 enter) // after hitting enter 11 is assigned to values[0] and 12 is assigned to weights[0]

this triggers next iteration of loop, console window looks as shown below:

hello 011 12 hello 1 now enter your two input:hello 113 14(13 space 14 enter) // after hitting enter 13 is assigned to values[1] and 14 is assigned to weights[1]

Now loop is terminated and your text after loop is print on the screen.

Catch here is each iteration of for-loop requires two int input from console (std::cin >> values[i] >> weights[i];)