HW Help - Reading from file character by character C++ - c++

Question

For a project I am currently working on, I have to read from a file and depending on the certain character in the file, output either a 1 or 0 to an array.
So here is an example of file input:
* * *
* * *
** ** **
*** *
And here is the function I have written to handle this:
void input (int cellGrid[][MAX]) //takes info from a .txt and puts it into an array
{
ifstream infile; //declare a file variable
int row;
int column;
int number;
infile.open("life.txt"); //open a file
while(infile>>row>>column) { //inserts bacteria places into array
cout << row << " " << column << endl;
cellGrid[row][column]=1; //makes it equal one if bacteria is present
}
infile.close(); //closes file
}
My thinking was that the function needs to see if there is a character that exists and if so, place a 1 in its respective position ([row][column]) in the array. However with this current code, nothing is input into my array.

Answer 1

Generally in C++ use std::vector wherever possible.
Array example:
You have to go through the file and record position of each *. Then set it to 1 for that position. Something like the following (we use getline and i as counter for rows, then we loop through the line using j as counter for columns):
#include <fstream>
#include <string>
using namespace std;
void input(int cellGrid[][100]) {
ifstream infile;
infile.open("life.txt");
int i = 0;
for (string line; getline(infile, line); ++i)
{
for (size_t j = 0; j < line.size(); ++j) {
if (line[j] == '*') {
cellGrid[i][j] = 1;
}
}
}
infile.close();
}
Vector example #1:
Here you can find a solution using std::vector. It will be always in a size rows x columns. One thing it requires is to pass default constructed vector and not constructed with vector(size_type count); c-tor. You can write your own version that doesn't have this problem:
#include <fstream>
#include <string>
#include <vector>
using namespace std;
void input(vector<vector<int>> &cellGrid) {
ifstream infile;
infile.open("life.txt");
int i = 0;
for (string line; getline(infile, line); ++i)
{
cellGrid.push_back(vector<int>(line.size()));
for (size_t j = 0; j < line.size(); ++j) {
if (line[j] == '*') {
cellGrid[i][j] = 1;
}
}
}
infile.close();
}
int main() {
vector<vector<int>> cellGrid;
vector<vector<int>> cellGrid2(100);
input(cellGrid);
//input(cellGrid2); - THIS WILL THROW AN EXCEPTION
return 0;
}
Vector example #2:
It would be even better for you function to return a newly created and populated vector:
#include <fstream>
#include <string>
#include <vector>
using namespace std;
vector<vector<int>> input() {
ifstream infile;
infile.open("life.txt");
vector<vector<int>> cell_grid;
int i = 0;
for (string line; getline(infile, line); ++i)
{
cell_grid.push_back(vector<int>(line.size()));
for (size_t j = 0; j < line.size(); ++j) {
if (line[j] == '*') {
cell_grid[i][j] = 1;
}
}
}
infile.close();
return cell_grid;
}
int main() {
auto vec = input();
return 0;
}

Answer 2

My thinking goes like this:
set row to 0
while can read a line from file
set column to 0
for each character on line
if character is '*'
set cellGrid(row,column) to 1
else
set cellGrid(row,column) to 0
increment column
increment row
You may want additional logic to trap row or column trying to go out of bounds or characters that aren't ' ' or '*'.