Passing 2d array to a function in C with pointers

You can afford to use far fewer asterisks, like this. Note that the printing code reverses the order of the subscripts compared to your code.

#include <stdio.h> #define TAM 2 void printMatriz(int matriz[TAM][TAM]); int main(void) { int matriz[TAM][TAM]; for (int i = 0; i < TAM; i++) { for (int j = 0; j < TAM; j++) { printf("Matriz[%i][%i] = ", i, j); if (scanf("%i", &matriz[i][j]) != 1) { fprintf(stderr, "failed to read an integer\n"); return 1; } } } printMatriz(matriz); return 0; } void printMatriz(int matriz[TAM][TAM]) { for (int i = 0; i < TAM; i++) { for (int j = 0; j < TAM; j++) printf("%i\t", matriz[i][j]); // Reversed order of i, j printf("\n"); } } 

Sample run:

Matriz[0][0] = 19 Matriz[0][1] = 28 Matriz[1][0] = 30 Matriz[1][1] = 41 19 28 30 41 

Note that this uses C99 notation for the for loops, avoiding the need for the variables i and j outside the loops. If it's a problem, reinstate the variable definitions outside the loops.

If you really want to use pointers to matrices, you could use either of these two variants of your code:

#include <stdio.h> #define TAM 2 void printMatriz(int (*matriz)[TAM]); int main(void) { int matriz[TAM][TAM]; for (int i = 0; i < TAM; i++) { for (int j = 0; j < TAM; j++) { printf("Matriz[%i][%i] = ", i, j); if (scanf("%i", &matriz[i][j]) != 1) { fprintf(stderr, "failed to read an integer\n"); return 1; } } } printMatriz(matriz); return 0; } void printMatriz(int (*matriz)[TAM]) { for (int i = 0; i < TAM; i++) { for (int j = 0; j < TAM; j++) printf("%i\t", matriz[i][j]); printf("\n"); } } 

Or:

#include <stdio.h> #define TAM 2 void printMatriz(int (*matriz)[TAM][TAM]); int main(void) { int matriz[TAM][TAM]; for (int i = 0; i < TAM; i++) { for (int j = 0; j < TAM; j++) { printf("Matriz[%i][%i] = ", i, j); if (scanf("%i", &matriz[i][j]) != 1) { fprintf(stderr, "failed to read an integer\n"); return 1; } } } printMatriz(&matriz); return 0; } void printMatriz(int (*matriz)[TAM][TAM]) { for (int i = 0; i < TAM; i++) { for (int j = 0; j < TAM; j++) printf("%i\t", (*matriz)[i][j]); printf("\n"); } } 

Note the different notations needed in the last example — in the call (like in your original code) and in the use of the matrix.

You could do in this way:

#include <stdio.h> #define TAM 2 void printMatriz(int **matriz); int main(void) { int **matriz=(int**)malloc(sizeof(int)*TAM); for (int i = 0; i < TAM; i++) { matriz[i]=(int*)malloc(sizeof(int)*TAM); for (int j = 0; j < TAM; j++) { printf("Matriz[%i][%i] = ", i, j); if (scanf("%i", &matriz[i][j]) != 1) { fprintf(stderr, "failed to read an integer\n"); return 1; } } } printMatriz(matriz); return 0; } void printMatriz(int **matriz) { for (int i = 0; i < TAM; i++) { for (int j = 0; j < TAM; j++) printf("%d ", matriz[i][j]); printf("\n"); } } 

I want to pass the pointer of a 2d array

You can pass a pointer to the first element of the 2D array and access all the elements using that pointer like so:

#define TAM 2 void printMatrix(int * matrix); //function prototype void printMatrix(int * matrix) { int i, j; for(i = 0; i < TAM; i++) { for(j = 0; j < TAM; j++) { printf("%i\t", *(matrix + i*TAM + j)); } printf("\n"); } } 

In your main function you would do something like this:

int main() { int i, j, matrix[TAM][TAM]; for(i = 0; i < TAM; i++) { for(j = 0; j < TAM; j++) { printf("matrix[%i][%i] = ", i, j); scanf("%i", &matrix[i][j]); } } printMatrix(&matrix[0][0]); //could also do this other ways (e.g. matrix[0], *matrix) just wanted to make it explicit that you are passing a pointer to the first element of the 2D array return 0; } 

I managed to make it work, but I still get the following warning:

||=== Build: Debug in matriz (compiler: GNU GCC Compiler) ===| C:\Users\pauli\.dev\c\uvv\matriz\main.c||In function 'main':| C:\Users\pauli\.dev\c\uvv\matriz\main.c|15|warning: passing argument 1 of 'printMatriz' from incompatible pointer type [-Wincompatible-pointer-types]| C:\Users\pauli\.dev\c\uvv\matriz\main.c|4|note: expected 'int * (*)[2]' but argument is of type 'int (*)[2][2]'| C:\Users\pauli\.dev\c\uvv\matriz\main.c||In function 'printMatriz':| C:\Users\pauli\.dev\c\uvv\matriz\main.c|23|warning: format '%i' expects argument of type 'int', but argument 2 has type 'int *' [-Wformat=]| ||=== Build finished: 0 error(s), 2 warning(s) (0 minute(s), 0 second(s)) ===| ||=== Run: Debug in matriz (compiler: GNU GCC Compiler) ===| 

Your warnings are stemming from a misunderstanding of how you defined your function and then what you passed it. As others have stated, your function is defined as taking an argument of a 2D array of pointers to integers int * matrix[][], and since the name of the array is itself a pointer to the beginning of that array, the function wants a pointer to a pointer (remember the first element of int * matrix[][] will be a pointer to an int) but then you pass it &matrix which is int * (a pointer to an int) because the first element of the 2D array matrix is an int.