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reading ints from text file one char at a time into array?

Feb 22, 2010 at 12:49am
MyrtleTurtle (4)
Hello. This is my first post here. I am having a little trouble with my C++ program (using Dev-C++).

The program is supposed to read in a line from a text file into an array and then multiply the array by another int array (which I will get to, later).

I know how to read a line, one char at a time, into an array as a string, but how do you do this using only ints?

If the file has
124
222
333

I want my first array to end up as:
ary[0] = 1;
ary[1] = 2;
ary[2] = 4;

and the second one to contain the second line, so that these two numbers can be multiplied.

Here is my code so far, although I know it is not quite correct. Any help would be much appreciated.

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#include<iostream>
#include<fstream>
#include<conio.h>

using namespace std;
const int SIZE = 25;

int main() {
	ifstream inFile;
	ofstream outFile;
	char num = '0';
    string num1[SIZE]; 
    string num2[SIZE]; 
    string ans[SIZE];
    
	inFile.open("BigNumbers.txt");
	
	if(!inFile){
	    cout<<"Error opening file.";
	    return 0;
	}
	
	num = inFile.get(); //priming read	
	while(inFile.good()){//loop while extraction from file is possible
	    for(int i = 0; i<SIZE; i++){ //read one line into one array
     	    num1[i] = num; 
            num = inFile.get(); // get another character from file
         }
         //here's where I would put the code to perhaps call a function
         //to convert the contents of the array into ints and save them
         //in another array?
         //I need to have three total, so we can multiply two large numbers
         //(in two arrays) and hold the result in the third one
         //but I have to get the numbers to multiply, one at a time from
         //the file
    }
	   cout<<endl; 
	for (int i =0; i<SIZE; i++){
		cout<<num1[i]<<", ";
		}

	
getch();
return 0;
}
Edit & run on cpp.sh
Feb 22, 2010 at 1:31am
tummychow (1210)
You could try
istream >> acharvariable;
and then convert it to integer using the atoi() function which I believe is in cctype. I can't say for sure however because I'm not too good with file IO. Try it and see.
Feb 22, 2010 at 1:31am
tummychow (1210)
Damn, another double post...
Last edited on Feb 22, 2010 at 1:32am
Feb 22, 2010 at 2:30am
MyrtleTurtle (4)
Thanks for the reply.

This does not work, though.
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	while(inFile.good()){//loop while extraction from file is possible
	    for(int i = 0; i<SIZE; i++){ //read one line into one array
   		    //convert char num to int & place in array
   		    numInt = atoi(num);
     	    num1[i] = numInt; 
            num = inFile.get(); // get another character from file
         }

    }


error: invalid conversion from 'char' to 'const char*'

I'm not sure my C++ instructor would like me to use atoi anyway. Isn't that mostly for C?
Last edited on Feb 22, 2010 at 2:33am
Feb 26, 2010 at 3:44pm
MyrtleTurtle (4)
Just in case anyone else would like to know, here is what I was supposed to do to get the numbers converted as we add them to the array:

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     int cnt = 0;            
         for(int i = 0; i<SIZE; i++){ //read one line into first array
             
             if(num != '\n'){//make sure it's not the end of the line
                 num1[i] = num - '0'; //convert from ascii to int
                 cnt++;//how many digits added to the array?
                 num = inFile.get(); // get another character from file
             }
             else{
                 break;//stop at the end of the line
             }
         }


//yes I know it's over-commented but it is for a class.
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