Creating a multi dimensional array at c

Question

Hello, need help creating a multi dimensional array i am new at C, any help is appreciated. this is the code

#include <stdio.h>

char init_board(int row, int col);

int main(int argc, char** argv) {
        int row = argv[3];
        int col = argv[4];
        char** board = init_board(row, col);

        for (int i = 0; i < row; i++) {
                for (int j = 0; j < col; j++) {
                        printf("%d", board[i][j]);
                }
        }


        return 0;
}

char init_board(int row, int col) {

        int count = 0;
        int count2 = 0;
        char** out;
        while (count < row) {
                while (count2 < col) {
                        out[count][count2] = ".";
                        count2++;
                }
                count++;
                count2 = 0;
        }
        return out;
}

any idea how i can fix this? what i am doing wrong? when i compile i receive following warnings and when i run it says segmentation fault

s@ss:~/s216/arc/ass1/ass1$ gcc ass1.c -std=c99 -o test
ass1.c: In function ‘main’:
ass1.c:6:12: warning: initialization makes integer from pointer without a cast [enabled by default]
  int row = argv[3];
            ^
ass1.c:7:12: warning: initialization makes integer from pointer without a cast [enabled by default]
  int col = argv[4];
            ^
ass1.c:8:17: warning: initialization makes pointer from integer without a cast [enabled by default]
  char** board = init_board(row, col);
                 ^
ass1.c: In function ‘init_board’:
ass1.c:27:23: warning: assignment makes integer from pointer without a cast [enabled by default]
    out[count][count2] = ".";
                       ^
ass1.c:33:2: warning: return makes integer from pointer without a cast [enabled by default]
  return out;
  ^
s@ss:~/s216/arc/ass1/ass1$ ./test x x 5 5
Segmentation fault
s@ss:~/s216/arc/ass1/ass1$

int row = argv[3]; Left hand side is an int, right hand side is a char *. That are not compatible types - exactly as the warning tells you. You need to convert argv[3] to an int with something like atoi or better still strtol. — kaylum
– kaylum, Commented Aug 3, 2016 at 5:00
Maybe this is completely irrelevant, but if everything is in bold, then nothing really stands out. Formatting is meant to draw attention to a specific part of the post, but if you draw attention everything, you may as well have drawn attention to nothing. — iRove
– iRove, Commented Aug 3, 2016 at 5:07

R Sahu · Accepted Answer · 2016-08-03 05:33:47Z

2

Type of argv[3] and argv[4] is char*. Hence, the lines

int row = argv[3];
int col = argv[4];

are wrong. You are trying to initialize two int objects with char*.

If you run the program using:

program 10 20 30 40

then,

The value of argv[0] will be "program".
The value of argv[1] will be "10".
The value of argv[2] will be "20".
The value of argv[3] will be "30".
The value of argv[4] will be "40".

Yes, they seem like they are numbers in the command line but they are strings in a C program. You can use atoi to extract the integral numbers from the strings.

int row = atoi(argv[3]);
int col = atoi(argv[4]);

Make sure to use

#include <stdlib.h>

to get the declaration of the function.

edited Aug 3, 2016 at 5:33

answered Aug 3, 2016 at 5:20

R Sahu

207k15 gold badges168 silver badges291 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

naffarn · Accepted Answer · 2016-08-03 05:35:18Z

1

When you write int row = argv[3]; you are making an int and initialising it to the value of argv[3]. However, argv is of type char **, which is a pointer to a pointer, or effectively an array of type char *. This is an invalid assignment, you need to make a char buffer to read the arguments in, then use atoi(argv[i]) to get the integer value.

edited Aug 3, 2016 at 5:35

answered Aug 3, 2016 at 5:09

naffarn

5735 silver badges13 bronze badges

Comments

Arc · Accepted Answer · 2017-12-04 17:37:56Z

0

the initially there was many errors with the code, i belive the following code is what it should have been..

#include <stdio.h>
#include <stdlib.h>

char **init_board(int row, int col);

int main(int argc, char** argv) {

        int row = atoi(argv[3]);
        int col = atoi(argv[4]);
        char** board = init_board(row, col);

        for (int i = 0; i < row; i++) {
                for (int j = 0; j < col; j++) {
                        board[i][j] = 'x';
                        printf("%c", board[i][j]);
                }
        }


        return 0;
}

char **init_board(int row, int col) {

        char** out = malloc(sizeof(char*) * row);
        for (int i = 0; i < row; i++) 
             out[i] = malloc(sizeof(char) * col);

        return out;
}

edited Dec 4, 2017 at 17:37

answered Dec 3, 2017 at 15:40

Arc

12 bronze badges

1 Comment

Anh Pham Over a year ago

Usually it's better to explain a solution instead of just posting some rows of anonymous code. You can read How do I write a good answer, and also Explaining entirely code-based answers

Collectives™ on Stack Overflow

Creating a multi dimensional array at c

3 Answers 3

Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related