what is the difference between int and int * in C

Question

i'm trying to compile a function to populate a matrix with zeros and ones as part of an adjacency matrix assignment but i keep getting errors when i use the make comma

this is the function that i have in a populateMat.c file.

#include "defs.h"
void PopulateMat(adjmat *mat[N][N]){

printf("\n the matrix size is [%d] x [%d]\n please enter connections between nodes.\n", N,N);
int i;
int j;
for ( i = 0; i < N ;i++){
    for ( j = 0; j < N ;j++)
    {
        printf("\n is there a connection between node %d to node %d ?\n yes - 1 \n no - 0\n", i, j);
        scanf("%d", mat[i][j]);
        if (!(&mat[i][j]==0 || (int)&mat[i][j]==1)) {
            printf("\n%d",mat[i][j]);
            printf("wrong indication inserted.\n insert 1 for yes \n 0 for no ");
            j--;
        }
    }
}

}

and this is the error when i run gcc -Wall -ansi -pedantic populateMat.c

populateMat.c: In function ‘PopulateMat’:
populateMat.c:13:19: warning: format ‘%d’ expects argument of type ‘int *’, but argument 2 has type ‘int (*)[3][3]’ [-Wformat=]
             scanf("%d", mat[i][j]);
                   ^
populateMat.c:15:24: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘int (*)[3][3]’ [-Wformat=]
                 printf("\n%d",mat[i][j]);
                        ^
/usr/lib/gcc/i686-linux-gnu/5/../../../i386-linux-gnu/crt1.o: In function `_start':
(.text+0x18): undefined reference to `main'
collect2: error: ld returned 1 exit status

my main.c is

int main()
{
    adjmat mat;                                    // defined in defs.h 
    typedef int adjmat [N][N];
    PopulateMat(&mat);
    printf("adjacency matrix received");
    // הדפסת מטריצת שכנויות
    printMat(mat);
    adjacency(&mat);
    return 0;
}

and Clion is giving this warning about populateMat(&mat) ** incompatible pointer types passing 'adjmat ' (aka 'int ( )[3][3]') to parameter of type 'adjmat ( )[3]' ** i've been trying to figure it out for way to long, help!

Answer 1

Your scanf("%d", mat[i][j]); : should be like this in for loop, scanf("%d", &mat[i][j]);

Function definition: void PopulateMat(adjmat *mat, N)

If statement code should look like this: if (!(mat[i][j]==0 || mat[i][j]==1)) No need to use & after ||

Answer 2

The typedef used to create an alias name for other data type. This statement

    typedef int adjmat [N][N];

creates adjmat an alias of int [N][N] type.

In this

void PopulateMat(adjmat *mat[N][N]){

the type of function parameter mat is adjmat *mat[N][N] , that means mat is of type adjmat *(*)[N] which is equivalent to int (*(*)[N])[N][N] .
In main() , you are passing &mat as argument to PopulateMat() . The type of &mat is adjmat * which is equivalent int (*)[N][N] .
The type of argument passed to PopulateMat() and type of parameter of PopulateMat() is not matching, hence you are getting incompatible type warning on this statement - PopulateMat(&mat); .

You should correct the type of PopulateMat() function parameter mat . It should be adjmat * :

void PopulateMat(adjmat *mat) {
 ....
 ....

the adjmat *mat is equivalent to int (*mat)[N][N] .

With this, you can access the i ^th row and j ^th column like this (*mat)[i][j] .
Note that scanf() expects pointer as argument. So, for taking input to i ^th row and j ^th column of mat , do this

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

---

Instead of passing address of mat to PopulateMat() function, you can pass mat as well because an array decays to pointer (with few exceptions).

So, you can also do

PopulateMat(mat);

and, in this case, the prototype of Populate() should be

void PopulateMat(adjmat mat);

here the type of mat is int (*)[N] (array to pointer decay only happen for inner most dimension).

With this, in the Populate() function, you can access the i ^th row and j ^th column of mat like this mat[i][j] .

Hope this helps.