How do I store the sums of the elements in each row of a 2d array in 1d array with a function?

Question

I have the following task: Create a 2d array A[M][N], where M and N are inputted by the user as well the elements in each row and column. There must also be two functions: 1)The first one needs to calculate the average of all positive numbers in the 2d array. This function works just fine, at least I think so.

2)Here is where my problem is and I simply ran out of options. The second function needs to create a new array B whose elements are the sums of the elements in each row in array A. After that it needs to print out array B.

The problem is as follows: Upon inputting 2 and 2 for M and N, as well as "2" for each of the elements in the 2x2 array (I have tried with 3 everywhere too), the second function should print out array B with elements "4 4". It, however, prints out 4 and 0. When trying 3 for every prompt it printed out the first element just fine-"9" the other 2 elements should also be 9, however the program just spewed some random numbers.

The code in question:

#include <stdio.h>
#include <math.h>
#include <string.h>
//1.
float average(int Y, int X, int A[Y][X]){
    float sum=0;
    float br=0;
    int k,r;
    for(k=0;k<Y;k++){
        for(r=0;r<X;r++){
            if(A[k][r]>0){
                
                sum+=A[k][r];
                br++;
            }
        }
    }
    if(br>0){   
    return sum/br;
}
else
{
    return 0;
}

//2.
void SumArray(int arrA[10][10], int m, int n, int B[10][1]);
int main()
{
    int i,j,M,N;
    
    printf("INPUT ROWS:\n");
    scanf("%d", &M);
    getchar();
    
    printf("INPUR COLUMNS:\n");
    scanf("%d", &N);
    getchar();
    int A[M][N];

    
    for(i=0;i<M;i++)
    {
        for(j=0;j<N;j++)
        {
        printf("INPUT A[%d][%d]:", i,j);
        scanf("%d", &A[i][j]);
        }
    }
    printf("\n");
    printf("ARRAY A LOOKS LIKE SO:\n");
    
    for(i=0;i<M;i++)
    {
        for(j=0;j<N;j++)
        {
            printf("%d ", A[i][j]);
        }
        printf("\n");
    }
    
    int B[M][1];
    for(i=0;i<M;i++)
    {
        B[i][0]=0;
    }

    //1.
    float avg= average(M,N,A);
    printf("THE AVARAGE OF ALL POSITIVE ELEMENTS IS:\n%f\n", avg);
    //2.
    printf("ARRAY B LOOKS LIKE SO:\n");
    SumArray(A, M, N, B);
    
    return 0;
}
//2.
void SumArray(int arrA[10][10], int m, int n, int B[10][1])      
{

    int i,j;
    float sum;

    for( i = 0; i < m; i++)
    {
        sum=0;
        for( j = 0;j < n; j++)
        {
             sum+= arrA[i][j];              
        }
        B[i][0]=sum;
    }
    for(i=0;i<m;i++){
        printf(" %d ", B[i][0]);
    }
}

What I tried (I am a beginner when it comes to programming): Making array B a 2D array (it was 1D in the beginning), Swapping B[10] with B[m] and B[n], different compilers.

You've hard-wired `SumArray` to operate on 10x10 arrays, and 10x1 arrays. So that code will only work on arrays with those dimensions. Why? Why not declare the arguments the way you did in `average`? — Tom Karzes, Apr 03 '23 at 13:25
Please don't SHOUT (all caps is shouting and considered as rude). You won't get an answer faster. — Jabberwocky, Apr 03 '23 at 13:25

score 0 · Answer 1 · answered Apr 04 '23 at 08:57

0

You should use 1D array for B.

void SumArray(int M, int N, int A[M][N], int B[M]) {
  memset(B, 0, M * sizeof *B);
  for(int m = 0; m < M; m++)
  for(int n = 0; n < N; n++)
    B[m] += A[m][n];
}

...

int B[M];
SumArray(M, N, A, B);

answered Apr 04 '23 at 08:57

tstanisl

13,520
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score 0 · Answer 2 · answered Apr 04 '23 at 09:21

In your main function, the main 2-D array with data is a VLA (variable-length array):

    int i,j,M,N;
    ...
    int A[M][N];

Your average is compatible with this definition:

float average(int Y, int X, int A[Y][X])

But your SumArray function is not compatible:

void SumArray(int arrA[10][10], int m, int n, ...)

The SumArray function regards the MxN array as 10x10, and this messes up all the indexing. You should make all your definitions and declarations compatible. For example:

void SumArray(int m, int n, int arrA[m][n], int B[m])

Note: to make the syntax work, you have to make SumArray receive the dimensions before the VLA itself.

Another option: declare and define all your arrays as 10x10, use only MxN elements, leaving all the others unused. In this case, you should make sure both M and N are not greater than 10 (if the user enters e.g. 11, write an error message).

This is the only option if your compiler doesn't support VLA (some compilers don't).

How do I store the sums of the elements in each row of a 2d array in 1d array with a function?

2 Answers2