?
Solved

passing an array to a function

Posted on 2000-03-06
15
Medium Priority
?
258 Views
Last Modified: 2010-04-02
I want to calculate the sum of each row on a 2 dimension array. Also, I need to make it as a function using pointer as argument.But, the function couldn't work. Here is my code:

int **matrix; //matrix is a 2 dimension array.
void row(int **ptr,int n)

main()
{
/*another part of the code go in here to  calculate the value of matrix*/
  row(matrix,n);
}

void row(int **ptr,int n)
{
int sum_row,x=0,y=0;
 for (y=0; y<=n-1;y++)
   {
   sum_row=0;
   for (x=0;x<=n-1;x++)
     {
     sum_row=sum_row+*(*(ptr+x)+y);
     }
     printf("The sum of row %d is %d\n", y+1, sum_row);
  }
}

Is there anything wrong when I pass the point to the function?

Thank you very much. -Zheng
0
Comment
Question by:zhu_zheng
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 3
  • 2
  • 2
  • +6
15 Comments
 
LVL 33

Expert Comment

by:hongjun
ID: 2590330
Hope the below code is correct. One problem with your code is that the lower index of the 2D array must have a value.

#include <stdio.h>

void row(int ptr[10][10],int n);

void main()
{
    int n;
    int a[10][10];

      printf("Enter the number of integers you wish to enter > ");
    scanf("%d",&n);

      row(a,n);
}

void row(int ptr[10][10], int n)
{
   int i,j;
   int count=0;
   int total=0;

   printf("Enter the %d number of integers >\n",n);

   for ( i=0; i<=9; i++ )
   {
         total=0;
       for ( j=0; count<n && j<=9; j++ )
         {
           scanf("%d",&ptr[i][j]);
               total += ptr[i][j];
           count++;
         }
         printf("The total is for row %d is %d\n",i+1,total);
   }
}


hongjun
0
 
LVL 3

Expert Comment

by:ufolk123
ID: 2590333
What is the problem you are getting ?
0
 
LVL 84

Expert Comment

by:ozo
ID: 2590357
the function prototype is missing a ;
n is undefined in main
an uninitialised pointer is passed to row
and // is a c++ comment, not a c comment
0
What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

 

Author Comment

by:zhu_zheng
ID: 2590445
Thanks to hongjun's answer.The reason to reject the answer is because I need to use point as a argument instead of a known array.

I'd like to make my question clear. I have calculated the value of each element in a n*n array. In main(), I need to calculate the sum on each row by calling a function. The pointer should be used as an argument, since n is unknown. I run the following code, it end up "0" no matter what the matrix value is. Something must be wrong in passing the pointer to the function.Where is wwrong?

int n, **matrix;
 
void row(int **ptr,int n);

main()
{ printf("Enter the n value here:\n");
  scanf("%d",n);
 /* value of *(*(matrix+x)+y)will be calculate here */
  /*call function row*/
  row(matrix,n);
}

void row(int **ptr,int n)
{
int sum_row,x=0,y=0;
 for (y=0; y<=n-1;y++)
   {
   sum_row=0;
   for (x=0;x<=n-1;x++)
     {
     sum_row=sum_row+*(*(ptr+x)+y);
     }
     printf("The sum of row %d is %d\n", y+1, sum_row);
  }
}


0
 
LVL 1

Expert Comment

by:mahno
ID: 2590565
But, how U allocate memory for matrix?
0
 
LVL 2

Expert Comment

by:fremsley
ID: 2590606
Are you initializing 'matrix' like this?

for (int x = 0; x < n; ++x) {
  *(matrix+x) = malloc(n*sizeof(int));
  for (int y = 0; y < n; ++y) {
    *(*(matrix+x)+y) = somevalue();
  }
}
0
 
LVL 12

Expert Comment

by:pjknibbs
ID: 2590633
You need to multiply "y" by the row length to read the correct values for the array. Thus, your sum line should look like:

sum_row=sum_row+*(*(ptr+x)+(y * n));
0
 
LVL 3

Expert Comment

by:ufolk123
ID: 2590652
How are you using the output of
void row(int **ptr,int n)  function in main ?
Actually you could return the sum_row as a return value from row function if you are using it to calculate the sum for a row.

I feel better is you do the following.

int n,sum, **matrix;
 
void row(int **ptr,int n);

main()
{ printf("Enter the n value here:\n");
  scanf("%d",n);
 /* value of *(*(matrix+x)+y)will be calculate here */
  /*call function row*/
  row(matrix,n);
  /* Use sum here which contains value of matrix sum or you can
     have sum as a pointer argument to row() which will populate it with
       value of matrix sum*/
      printf("The sum of matrix is %d\n", sum);
}

void row(int **ptr,int n)
{
int sum_row,x=0,y=0;
 for (y=0; y<=n-1;y++)
   {
   sum_row=0;
   for (x=0;x<=n-1;x++)
     {
     sum_row=sum_row+*(*(ptr+x)+y);
     }
     printf("The sum of row %d is %d\n", y+1, sum_row);
       sum+=sum_row;
  }
}






0
 
LVL 1

Expert Comment

by:mahno
ID: 2590703
but U can't use 1D array like this?

int n, *matrix;
 
void row(int *ptr,int n);

main()
{
  int x, y;
  printf("Enter the n value here:\n");
  scanf("%d",&n);
  matrix = (int *)malloc(n*n*sizeof(int));
  for (x = 0; x < n; ++x) {
    for (y = 0; y < n; ++y) {
      *(matrix+x+y*n) = somevalue();
    }
  }

  row(matrix,n);
}

void row(int *ptr,int n)
{
 int sum_row,x=0,y=0;
 for (y=0; y<=n-1;y++)
 {  
   sum_row=0;
   for (x=0;x<=n-1;x++)
     {
     sum_row=sum_row+*(ptr+x+y*n);
     }
     printf("The sum of row %d is %d\n", y+1, sum_row);
  }
}

0
 
LVL 33

Expert Comment

by:hongjun
ID: 2590872
Are you using pointer? If yes then you may have to use malloc or alloc to allocate memory.

hongjun
0
 
LVL 5

Expert Comment

by:PC_User321
ID: 2591267
Since n is variable, we cannot do the proper thing and work with predefined structure types.  We have to create our own structure on-the-fly by multiplying the row number by n when we access the matrix, as was said by pjknibbs.
Here is a complete program that produces the output below when n is set to 5.

The sum of row 0 is 10
The sum of row 1 is 35
The sum of row 2 is 60
The sum of row 3 is 85
The sum of row 4 is 110



#include <stdio.h>
#include "malloc.h"

void addRow(int *ptr,int n);

void main()
{
  int  *matrix;
  int  column, row, n, k;

  k = 0;
  printf("Enter the n value here:\n");
  scanf("%d",&n);

  matrix= malloc(n*n*sizeof(int));
  /*fill the array with values.*/
  for( row=0; row<n; row++ ){
    for(column=0; column<n; column++) {
      *(matrix + row*n + column) = k++;
    }
  }
  /*call function addRow to print the sum of each row*/
  addRow(matrix,n);
}
}

void addRow(int *ptr,int n)
{
  int sum_row;
  int row=0;
  int column=0;

  for (row=0; row<n; row++)
  {
     sum_row=0;
     for (column=0; column<n; column++)
     {
       sum_row=sum_row+ *(ptr + row*n + column);
     }
     printf("The sum of row %d is %d\n", row, sum_row);
  }
}






0
 
LVL 2

Accepted Solution

by:
fremsley earned 150 total points
ID: 2591706
I think, this is what most people here consider the main point:

You have two basic choices on how to arrange your 'matrix' (assuming both dimensions to be 'N').

1. You allocate one array of N*N values.
    array = malloc(N*N*sizeof(int));
  Access to a cell is then:
    matrix[x*N + y] or *(matrix + x*N + y)

2. In your example you created an array of pointers pointing to row arrays. In this case both, the pointer array and each row must be allocated:
    array = malloc(N*sizeof(int *));
    for (i=0..N-1) array[i] = malloc(N*sizeof(int));
  Access to a cell is like this:
    array[x][y] or *(*(array+x)+y)

0
 
LVL 2

Expert Comment

by:fremsley
ID: 2591740
I seem to have mixed 'array' and 'matrix' above. Sorry
0
 

Expert Comment

by:jayak
ID: 2594982
Hi,
  He wrongly placed the fields x and y.
Find below is the program and output. I hope it will do for him.
Assumed : To calculate the sum of row values.

# include <stdio.h>
int **matrix;
void row(int **ptr,int n);

main()
{
 int n = 4;
int   val1[4]={1,2,3,4},
        val2[4]={10,20,30,40}, val3[4]={100,200,300,400},
        val4[4]={1000,2000,3000,4000};
int   *ip[4];
    ip[0] = val1;
    ip[1] = val2;
    ip[2] = val3;
    ip[3] = val4;

  matrix = ip;
/*another part of the code go in here to  calculate the value of matrix*/
  row(matrix,n);
}

void row(int **ptr,int n)
{
int sum_row,x=0,y=0,old_value;
 for (y=0; y<=n-1;y++)
   {
   sum_row=0;
   old_value = 0;
   for (x=0;x<=n-1;x++)
     {
     old_value = sum_row;
     sum_row=sum_row+*(*(ptr+y)+x);
     old_value = sum_row - old_value;
     printf("The value is %d \n",old_value);
     }
     printf("The sum of row %d is %d\n", y+1, sum_row);
  }
}

Output :
----------
The value is 1
The value is 2
The value is 3
The value is 4
The sum of row 1 is 10
The value is 10
The value is 20
The value is 30
The value is 40
The sum of row 2 is 100
The value is 100
The value is 200
The value is 300
The value is 400
The sum of row 3 is 1000
The value is 1000
The value is 2000
The value is 3000
The value is 4000
The sum of row 4 is 10000
0
 

Author Comment

by:zhu_zheng
ID: 2596906
My question is very well answered by many people.
Thank you all for your intelligent inputs and your kindly heart.
Thanks,
-Zheng
0

Featured Post

Technology Partners: We Want Your Opinion!

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Windows programmers of the C/C++ variety, how many of you realise that since Window 9x Microsoft has been lying to you about what constitutes Unicode (http://en.wikipedia.org/wiki/Unicode)? They will have you believe that Unicode requires you to use…
Examines three attack vectors, specifically, the different types of malware used in malicious attacks, web application attacks, and finally, network based attacks.  Concludes by examining the means of securing and protecting critical systems and inf…
The goal of this video is to provide viewers with basic examples to understand how to use strings and some functions related to them in the C programming language.
The goal of this video is to provide viewers with basic examples to understand and use switch statements in the C programming language.

718 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question