Thread: homework help! find diagonal sum of matrix

Hi, I need some help with my code.

My assignment is to
Write a C program that finds thesum of the diagonal elements of a matrix. Specifically, the programshould first prompt the user to input the number of rows and columnsof the matrix, then prompt the user to input its elements, then printthe matrix the user entered and finally print the sum of the diagonalelements. You can assume that the maximum number ofrows and columns the user inputs is 10, that the number of rows andcolumns the user enters are always equal, and the elements of thematrix to be integer numbers.

Implementation Requirements:

1. Implement a function called “findDiagSum” to find the sum of the diagonal elements. The function should return the sum of the diagonal elements (which would be an integer number). Define the function prototype appropriately in your program. (Carefully think over the arguments of the function)
   
   2. Implement a function called “print_matrix”, whose prototype is—
   
   
   “voidprint_matrix(int mat[10][10], int r, int c);”
   Define the functionprototype in your program.
   
   
   Code:

   
   
   void print_matrix(int mat[10][10], int r, int c);
   int findDiagSum();
   
   
   void main()
   {
       int mat[10][10], r, c, i, j, ssum;
   
   
   
   
       ssum = findDiagSum();
       printf("The sum of the diagonal elements is &ssum");
   }
   
   
   void print_matrix(int mat[10][10], int r, int c)
   {
       int i, j;
       printf("\nEnter the rows and columns of the matrix: ");
       scanf("%d %d", &r, &c);
   
   
       printf("\nEnter the elements of the matrix: ");
       for(i=0; i<r; i++)
           for(j=0; j<c; j++)
               scanf("%d", &mat[i][j]);
       printf("\nThe matrix is\n");
   }
   
   
   int findDiagSum()
   {
       int mat[10][10], r, c, i, j, sum=0;
   
   
       for(i=0; i<r; i++)
           for(j=0; j<c; j++)
           {
            if (i==j)
            sum = sum + mat[i][j];
           }
       return sum;
   }

   I am not sure how to call the void print_matrix function into the main function. If somebody could help me with this and also give me some insight to make sure my whole code looks good. Thanks for all your help in advance.

When you call a function, you typically remove the return data type, as well as the data types from the parameters. They're already known, from the prototype you have.

Just use the name of the array, and the name of the variables (for a pass by copy: r for example), or the address of the named variables (for a pass by reference: &r).

Try that.

I'm sorry, I am not sure I understand still. If you could explain further or give me an example, it would be much appreciated.

ok. I got the print matrix part of the program to work, but now the sum of the diagonal part is giving me some trouble, the numbers are not summing to what they should. If anybody could help with this, it would be much appreciated, thank you for all your help i advance.

Code:

int main()
{
    int a, b, ssum;


    print_matrix(&a, &b);
    ssum = findDiagSum();
    printf("The sum of the diagonal elements is %d", ssum);


    return 0;
}


void print_matrix(int mat[10][10], int r, int c)
{
    int i, j;
    printf("\nEnter the rows and columns of the matrix: ");
    scanf("%d %d", &r, &c);


    printf("\nEnter the elements of the matrix: ");
    for(i=0; i<r; i++)
        for(j=0; j<c; j++)
            scanf("%d", &mat[i][j]);
    printf("\nThe matrix is\n");
    for(i=0;i<r;i++)
      {
      printf("\n");
      for(j=0;j<r;j++)
      {
      printf("%d\t",mat[i][j]);
      }
      }
}


int findDiagSum()
{
    int mat[10][10], r, c, i, j, sum=0;


    for(i=0; i<r; i++)
        for(j=0; j<c; j++)
        {
         if (i==j)
         sum = sum + mat[i][j];
        }
    return sum;
}

You should be passing a 2d array into your print matrix. Look in main and tell me what you are passing it. You also have a random 2d array in your findSum function, the matrix should be passed in from main.

I just wanted to thank everyone for their help. I finally got it!

little problem, if anyone could help me with this, it would be much appreciated.
my program works for matrix size of 1-5, but when trying 6-10, it just crashes, any help would be much appreciated.

Code:

int main()
{
    int a, b, ssum;


    print_matrix(&a, &b); // prints user input matrix by print_matrix function
    ssum = findDiagSum(&a, &b); // finds sum of diagonal elements by findDiagSum function
    printf("The sum of the diagonal elements is %d", ssum);


    return 0;
}


void print_matrix(int mat[10][10], int r, int c)
{
    int i, j;
    printf("\nEnter the rows and columns of the matrix: ");
    scanf("%d %d", &r, &c); // user enters rows and colums of matrix


    printf("\nEnter the elements of the matrix: ");
    for(i=0; i<r; i++)
        for(j=0; j<c; j++)
            scanf("%d", &mat[i][j]); // user enters elemets of the matirx
    printf("\nThe matrix is\n");
    for(i=0;i<r;i++) // prints matrix with user input elements
      {
      printf("\n");
      for(j=0;j<r;j++)
      {
      printf("%d\t",mat[i][j]);
      }
      }
}


int findDiagSum(int mat[10][10], int r, int c)
{
    int i, j, sum=0;
    for(i=0; i<r; i++)
        for(j=0; j<c; j++)
        {
         if (i==j) // finds diagonal elements of the matrix
         sum = sum + mat[i][j]; // diagonal elements are summed together
        }
    return sum; // returns the sum of the diagonal elements
}

Does it compile?

yes, it does and the program also work for matrix sizes 1x1, 2x2, 3x3, 4x4, 5x5. any bigger than that it crashes.

The functions you've got aren't consistent (in terms of parameters), so there's no way this is actually your code. Who knows what else you've changed between this version and that?