Bdtjtk

So, I have to create a program that, when the user inserts a table, has to send in output only the border of the table. I used a matrix for the input but when the user ends the input, the program stops and I get segmentation fault.

#include <stdio.h>

#define VAL 50



void inputMatrice(int m[VAL][VAL], int *ncol, int *nrig);

void bordi(int m[VAL], int ncol, int nrig, int v, int *nv);

void outputVettore(int v, int nv);



int main(){

    int m[VAL][VAL], v[VAL], *ncol, *nrig, nc, nr, nv;

    ncol = &nc;

    nrig = &nr;

    inputMatrice(m, ncol, nrig);

    nv=0;

    printf("ciao");

    bordi(m, nc, nr, v, &nv);

    outputVettore(v, nv);



}

/*Funzione per input matrici*/



void inputMatrice(int m[VAL][VAL], int *ncol, int *nrig){



    int i=0, j=0;

    printf("Inserisci il numero di righe: ");

    scanf("%d", nrig);

    printf("Inserisci il numero di colonne: ");

    scanf("%d", ncol);

    for(i=0;i<*nrig;i++){

        for(j=0;j<*ncol;j++){

            printf("Inserisci i valori della tabella nella posizione %d,%d: ", i+1, j+1);

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

        }

    }

}



void bordi(int m[VAL], int ncol, int nrig, int v, int *nv){

    int i=0, j=0, k=0;

    for(j=1; j<ncol; j++){

        v[k]=m[i][j];

        *nv++;

    }

    for(i=1;i<nrig;i++){

        v[k] = m[i][j];

        *nv++;

    }

    for(j=(ncol-1); j>0; j++){

        v[k]=m[i][j];

        *nv++;

    }

    for(i=(nrig-1); j>0; i++){

        v[k]=m[i][j];

        *nv++;

    }

}

void outputVettore(int v, int nv){

    int i=0;

    for(i=0;i<nv;i++){

        printf("|%d|", v[i]);

    }



}

Sorry for the italian Output and for the bad english.

The error occurs in
void bordi(int m[VAL], int ncol, int nrig, int v, int *nv) function.

Fix 3rd and 4th for loops conditions. You incremented j in first loop but didn't decrement or set it to 0, so you get an infinite loop.

The line in your program *nv++; increments the pointer which is totally wrong in logic, try incrementing the value .
that is, Try :-
(*nv)++;

The problem is in function bordi(). Look at this for loop:

for(j=(ncol-1); j>0; j++){

    v[k]=m[i][j];

    *nv++;

}

The loop control variable j initialize with ncol-1 and checking for condition j>0. After executing the loop statements, the j will be incremented by 1 (j++). So the loop condition j>0 will always true [until the j overflows] and after few iterations your program starts accessing invalid value of array m (m[i][j]) which is causing the segmentation fault.

To fix this problem, replace j++ with j-- in the loop.

The same problem exists in the next for loop as well but in a little different way:

for(i=(nrig-1); j>0; i++){

    v[k]=m[i][j];

    *nv++;

}

here, in the loop condition you are using variable j.

You need to do two changes in this for loop.

for(i=(nrig-1); i>0; i--){

                ^^   ^^