CODEWITHSUNDEEP
c++arrays
Sam
Sam

Reputation: 31

Two lines causing print error

Hi my program is supposed ask for an input of grades and then output the number of times those grades occur. The number of times that occurs is shown by tally markers, I am using "*" as the tally marker. My current code outputs this:

Enter number of grades:
4
Enter grades:
1
5
10
10
10
Histogram:
0
1 *
2
3
4
5 *
.
.
10 **

As you can see the number of grades I am asking for is 4, but it requires 5 inputs and doesn't seem to count the 5th. Also it prints out the numbers in between instead of just the scores. What I am trying to achieve is

Enter number of grades:
4
Enter grades:
1
5
10
10
Histogram:
1 *
5 *
10 **


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

using namespace std;

int main(){   
    int n;
    int value = 0;
    vector<int> grades;
    cout<<"Enter number of grades:"<<endl;
    cin >> n; 
    cout <<"Enter grades: "<<endl;
    cin >> value;

    for (int i=0; i<n; i++) // believe this condition is wrong, causing the input extra number. I've tried multiple variations and can not figure it out.

    {
        grades.push_back(value);
        cin >> value;
    }

    int max = 0;
    for(int i=0; i<grades.size(); i++)
    {
        if(grades[i] > max) 
            max = grades[i];
    }

    int* array= new int[max+1];

    for(int i=0; i<grades.size(); i++)
    {
        array[grades[i]]++;
    }

    cout<<"The histogram is:"<<endl;

    for(int i=0; i<=max; i++){
    if(array[i]!=0)

        char stuff;
       std::string stuff(array[i], '*'); //pretty sure this is causing all the numbers to be printed, but I don't know another way to print the asterisk 



    cout<<i <<" "<<stuff<<std::endl;

    }    
    return 0;    
}

Why is it printing all the numbers, when the line to print the asterisk is included? When I take out the line for printing the asterisk, it no longer prints all the numbers, but of course it also does not print the asterisk.

Upvotes: 0

Views: 79

Answers (4)

zicai
zicai

Reputation: 3

cin >> value;    // input:1

for (int i=0; i<n; i++) 
{
    grades.push_back(value);
    cin >> value;// input:5,10,10,10, this is why you need to enter extra number(10),
                 // but the last number is never used
}

Upvotes: 0

bgoldst
bgoldst

Reputation: 35324

Problems:

  1. Illogical reading code. You read the first grade outside of the for-loop, but then unconditionally read a grade inside the for-loop after pushing the previous grade onto the vector. You need to read one grade and push it in every iteration; there should be no reads before or after the loop.
  2. Not initializing the new int array to zeroes. This can be done with an initializer, meaning a pair of parentheses. See Operator new initializes memory to zero.
  3. Omitting the braces around the final if-block inside the histogram-printing loop. You need the braces, because nothing should happen inside that loop unless the count is non-zero for the current iteration.
  4. Unused variable declaration char stuff;. Also, if you fix #3, then this would become a redeclaration and would cause a compiler error.

Fixed code:

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

using namespace std;

int main() {

    int n;
    int value;
    vector<int> grades;

    cout << "Enter number of grades:" << endl;
    cin >> n;

    cout << "Enter grades: " << endl;
    for (int i = 0; i < n; ++i) {
        cin >> value;
        grades.push_back(value);
    } // end for

    int max = 0;
    for (int i = 0; i < grades.size(); ++i)
        if (grades[i] > max)
            max = grades[i];

    int* count = new int[max+1]();

    for (int i = 0; i < grades.size(); ++i)
        ++count[grades[i]];

    cout << "The histogram is:" << endl;
    for (int i = 0; i <= max; ++i) {
        if (count[i] != 0) {
            std::string stuff(count[i],'*');
            cout << i << " " << stuff << std::endl;
        } // end if
    } // end for

    return 0;

} // end main()

Upvotes: 0

Revathi Muthukrishnan
Revathi Muthukrishnan

Reputation: 47

Add = sign in the for condition i.e 1<=n May this solve your issue.

for (int i=0; i<=n; i++)

Upvotes: -1

R Sahu
R Sahu

Reputation: 206717

The logic in these lines is incorrect. Let's say n is 1.

cin >> value; // Read the first number

for (int i=0; i<n; i++)
{
    grades.push_back(value); // Push the first number
    cin >> value;            // Unnecessary input, which doesn't get used.
}

You need:

for (int i=0; i<n; i++)
{
   cin >> value;
   grades.push_back(value);
}

Upvotes: 2

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