Function with bidimensional array as parameter

Question

I read that to declare a function with a bidimensional array as parameter, I need to specify the number of columns of the array, but if I don't know the size of the matrix I need to use double pointer. However, I can't understand this process very well, can someone give me some short and simple example of this type of function?

Thank you

Also, I tried to write a program but it gives me some warning.

#include<stdio.h>

int diagonal(int**,int );--->first note

int main(){
    int N;
    scanf("%d",&N);
    int array[N][N];
    int i;
    int j;
    printf("Insert the numbers:\n");
    for(i=0;i<N;i++){
            for(j=0;j<N;j++){
            scanf("%d",&array[i][i]);
          }
    }
    diagonal(&array[N][N],N); ---->second warning
}

int diagonal(int**A,int N){
    int i;
    int condition=0;
    for(i=0;i<N-1;i++){
       if(A[0][0]!=A[i+1][i+1]){
          return -1;
       }else{
          condition=1;
       }
   }
   if(condition==1){
      int val=A[i][i];
      int sum= N*val;
      return sum;
   }
}

Compiler output:

3|note: expected 'int **' but argument is of type 'int *'|

17|warning: passing argument 1 of 'diagonal' from incompatible pointer type|


||=== Build finished: 0 error(s), 1 warning(s) (0 minute(s), 0 second(s)) ===|

The program should scan a matrix and return the sum of elements on the main diagonal if the elements on the diagonal have the same value return -1 if not.

dbush · Accepted Answer · 2016-06-23 17:03:27Z

2

If you want to use a variable size array as an argument, you need to specify the size first, then use that parameter as the array size in the array argument:

int diagonal(int N, int A[N][N] );

int main() {
    ...
    diagonal(N, array);
}

int diagonal(int N, int A[N][N]){
    ...
}

answered Jun 23, 2016 at 17:03

dbush

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3 Comments

Giorgio M. Over a year ago

I'm sorry if the question may sounds dumb,but i'm a beginner.In the declaration shoudn't i delete the "N" parameters? i mean if i put int diagonal(int N, int A[N][N] ); the compiler says that "N" is undeclared and if i delete "N" the program won't run

dbush Over a year ago

@GiorgioM. In most cases, the parameter names in a declaration are not required, but in this case it's needed to let the compiler know it's dealing with a variable sized array and what specifies the size. Attempting to declare the array parameter as int [][] is an incomplete declaration.

Giorgio M. Over a year ago

Ahhh nevermind now it works . Thank you so much and thank you to all the people that answered

V. Kravchenko · Accepted Answer · 2016-06-23 17:01:36Z

1

You are passing your array wrong. You should pass array instead of &array[N][N]. When you do &array[N][N] you just get address of [N][N] array's element and pass it, it is invalid address.

diagonal(array, N);

Also, when you do scanf, you, probably wanted to get [i][j] element, but you do [i][i] two times.

scanf("%d", &array[i][j]);

answered Jun 23, 2016 at 17:01

V. Kravchenko

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Comments

Cherubim · Accepted Answer · 2016-06-23 17:05:55Z

1

17|warning: passing argument 1 of 'diagonal' from incompatible pointer type|

diagonal(&array[N][N],N); //---->warning

here &array[N][N] is of the type int* but your function definition:

int diagonal(int**,int );

has first argument type as int** so you are sending wrong type as an argument. that's the reason why you are get this warning.

edited Jun 23, 2016 at 17:05

answered Jun 23, 2016 at 16:58

Cherubim

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