cin crashing my program after 12 for loop iterations? - c++

Question

I've never posted here before but I'm really stuck so I thought i'd give it a try. I've been working on this code for a while, The aim is to input a few students with their marks and to output them into tables with averages and totals. I was given a file like this:
15
Albert Einstein 52 67 63
Steve Abrew 90 86 90 93
David Nagasake 100 85 93 89
Mike Black 81 87 81 85
Andrew Van Den 90 82 95 87
Joanne Dong Nguyen 84 80 95 91
Chris Walljasper 86 100 96 89
Fred Albert 70 68
Dennis Dudley 74 79 77 81
Leo Rice 95
Fred Flintstone 73 81 78 74
Frances Dupre 82 76 79
Dave Light 89 76 91 83
Hua Tran Du 91 81 87 94
Sarah Trapp 83 98
my problem is that when I am inputting the names the program crashes after Fred Flinstone, I know its not a problem with the formatting of the next name (Frances Dupre) because when i moved him up the list it read it fine.
I have located where the program is crashing with 'cerr' outputting at different stages of the read process and it crashes when it is trying to read in Frances's marks.
a1main.cpp
#include <iostream>
#include "student.h"
using namespace std;
int main()
{
int numStds;
cin >> numStds;
cerr << endl << "Num Stds: " << numStds << endl;
Student std[numStds+1];
for(int i = 0; i <= numStds; i++)
{
std[i].readData();
std[i].printStudent();
}
// delete [] std;
return 0;
}
student.h
#include <iostream>
using namespace std;
class Student {
private:
char* name;
int mark[4];
int num;
public:
Student();
~Student();
void readData();
void printStudent();
float getTotal();
float getAverage();
};
student.cpp
#include <iostream>
#include <cstring>
#include <cctype>
#include "student.h"
using namespace std;
Student::Student()
{
name = new char;
mark[0] = 0;
mark[1] = 0;
mark[2] = 0;
mark[3] = 0;
num = 0;
}
Student::~Student()
{
// Doesn't work?
// delete name;
}
void Student::readData()
{
int l = 0;
// Reading the Name
cin >> name; // Read in the first name
l = strlen(name); // get the strlength
name[l] = ' '; // Putting a space between the first and last name
cin >> &name[l+1]; // Read in the last name
cerr << endl << "I have read the name!" << endl;
// Checking if there is a third name
if(cin.peek() == ' ')
cin >> ws; // checking and navigating past the whitespace
char next = cin.peek();
if( isalpha(next) ) // Checking whether the next cin is a char
{
l = 0;
l = strlen(name);
name[l] = ' ';
cin >> &name[l+1];
}
cerr << "I've checked for a third name!" << endl;
// Reading in the marks
for(int i = 0; i < 4; i++)
{
// Checks if the next cin is a newline
if (cin.peek() == '\n')
break;
cin >> mark[i];
}
cerr << "I've read in the marks!" << endl;
//cerr << endl << "I have read " << name << "'s marks!" << endl << endl;
for(int m = 0; m < 4; m++)
{
if(mark[m] != 0)
{
num++;
}
}
cerr << "I've incremented num!" << endl << endl;
}
// Function for error checking
void Student::printStudent()
{
cout << endl << "Student Name: " << name << endl;
cout << "Mark 1: " << mark[0] << endl;
cout << "Mark 2: " << mark[1] << endl;
cout << "Mark 3: " << mark[2] << endl;
cout << "Mark 4: " << mark[3] << endl;
cout << "num marks: " << num << endl << endl;
}
float Student::getTotal()
{}
float Student::getAverage()
{}
Can anyone see what i'm doing wrong? thanks :)

Answer 1

You're never allocating memory to store the student names.
In your Student constructor, add this code:
name = new char[100]; // allows names up to 100 characters long
and uncomment this line in the destructor:
delete[] name;
You could also make the code more sophisticated and robust by measuring the name length and allocating the correct size, or use std::string as suggested below.