Thread: C - File IO and 2D Arrays

I am a student working on an assignment for school, and I am currently stuck with a problem. I am having trouble filling in my 2D array with integers from a text file. When I go to run and compile this it gives me absurd random numbers in my print out. I think I am not calling the function correctly or my pointer may be not in the correct position.

Text File:

Code:

43
Samantha Octavia Ivan Henry
100 90 65 70
99 50 70 88
88 90 98 100

Code:

#include <stdio.h>
#include <stdlib.h>
#define SIZE 100


//function prototype
void getNames(int students, char names [][SIZE], FILE * inputFile);
void getGrades (int assignments, int students, int grades[][students], char names[][SIZE], FILE * inputFile);
//void calcGrades(int assignments, int students, int grades [][students], char names[][SIZE]);
//void printGrades(int assignments, int students, int avg, int grades [][students], char lettergrade [] [students], char names[][SIZE]);




int main()
{
//variables
int students;
int assignments;
char string0 [100];
char char0;
FILE * inputFile;


//Open File
inputFile = fopen ("input.txt", "r");


//input
    if(    inputFile == NULL)
    {
        printf ("Unable to open file input.txt");
        exit(EXIT_FAILURE);
    }
    else
    {
        printf ("How many students?\n ");
        fscanf (inputFile, "%d", &students);
        printf ("%d", students);
        printf ("\nHow many assignments?\n ");
        fscanf (inputFile, "%d", &assignments);
        printf ("%d\n", assignments);
    }
//variables
char names[students][SIZE];
int grades[assignments][students];




//passing variables to funcs
    getNames (students,names,inputFile);
    getGrades (assignments,students,grades,names,inputFile);
//   calcGrades(assignments, students, grades, names);
//  printGrades(assignments, students, avg, grades, lettergrade, names);


    //fclose(inputFile);


    return 0;




}


void getNames (int students,char names [][SIZE], FILE * inputFile)
{
//variables
int i;


    for (i=0; i<students; i++) //counter for array size
    {
       printf ("\nEnter name for Student %d: ",i);
       fscanf (inputFile, "%s", names[i]);
       printf ("%s",names[i]);
    }
}


void getGrades (int assignments, int students, int grades [][students], char names[][SIZE], FILE * inputFile)
{
//variables
int i;
int j;


//counter loop
   printf ("\n");


   for (i=0; i < assignments; i++) //counter for array size
    {
       for (j=0; j < students; j++)
       {
            printf ("\nEnter grade for Assignment %d for %s: ",i,names[j]);
            fscanf (inputFile, "%d", &grades[j][i]);
       }
       printf ("%d", grades[i]);
    }
}

I think your biggest problem is that you try to print grades like this:

Code:

printf ("%d", grades[i]);

If you want to print grades, you should print each element out -- there is no real shortcut like printing grades[i] or something like that. What happens when you try to anyway is usually what you saw; grades[i] is a variable length array, and when you print an array, as opposed to an array element, what you see is a memory address (where the array is stored) instead of something useful.

Also this loop seems incorrect:

Code:

 
 
   for (i=0; i < assignments; i++) //counter for array size
    {
       for (j=0; j < students; j++)
       {
            printf ("\nEnter grade for Assignment %d for %s: ",i,names[j]);
            fscanf (inputFile, "%d", &grades[j][i]);
       }
       printf ("%d", grades[i]);
    }

The outer loop should probably be the students, and the inner loop should probably be the assignments.

Jim