Hey guys so Im trying to do a homework and I cant find the fatal error on my program all day long.Let me explain : Firstly,you give the number of rows,col then the cells of the array (only "." for free spaces and "*" for mines, all in one row without spaces) then the crashing happens.
main(){
int i,col,row,count,N,M,j;
char **p;
printf("Give number of rows\n");
scanf("%d",&N);
printf("Give number of columns\n");
scanf("%d\n",&M);
p=malloc(N*sizeof(char *)); //Saving room for the array
if (p==NULL)
return -1;
for (i=0;i < N ; ++i){
p[i] = malloc (M * sizeof(char));
if (*(p+i) == NULL)
return -1;
}
for (i=0; i< N;++i){
for ( j = 0 ; j < M ;++j)
scanf("%c",&p[i][j]); //Insert "*" for mines and the rest with "."
}
for (row=1; row<= N;++row){ //Here the things get messy
for ( col = 1 ; col <= M ;++col){
if(p[row][col]=='.'){
count = 0 ;
if(p[row][col+1]=='*' && col < M)
count=count+1;
if(p[row][col-1]=='*' && col > 1)
count=count+1;
if(p[row+1][col]=='*' && row < N)
count=count+1;
if(p[row-1][col]=='*' && row > 1)
count=count+1;
if(p[row+1][col+1]=='*' && (row < N && col < M))
count=count+1;
if(p[row+1][col-1]=='*' && (row < N && col > 1))
count=count+1;
if(p[row-1][col+1]=='*' && ( row > 1 && col < M))
count=count+1;
if(p[row-1][col-1]=='*' && ( row > 1 && col > 1))
count=count+1;
printf("%d ", count);
}
printf("* ");
}
printf("\n");
}
printf("\n");
for (i=0; i< N;++i){
for ( j = 0 ; j < M ;++j)
printf("%c ",p[i][j]);
printf("\n");
}
for (i = 0 ; i <N ; ++i)
free(p[i]);
free(p);
}
Firstly, here's what I did to debug (actually I saw the problem in the code and just verified this way, but this will be useful to you).
Add #include <stdio.h> and #include <stdlib.h> at the head of the file.
gcc -Wall -O0 -g x.c -o x to compile with debug and no optimisation.
I then used following to run within gdb:
gdb x
...
(gdb) run
Starting program: /home/amb/so/x
warning: no loadable sections found in added symbol-file system-supplied DSO at 0x7ffff7ffa000
Give number of rows
1
Give number of columns
1
.
Program received signal SIGSEGV, Segmentation fault.
0x00000000004007d4 in main () at x.c:25
25 if(p[row][col]=='.'){
(gdb) print row
$1 = 1
(gdb) print col
$2 = 1
(gdb)
See how in less than 10 seconds it showed me where the error was?
You have two problems:
for (row=1; row<= N;++row){ //Here the things get messy
for ( col = 1 ; col <= M ;++col){
if(p[row][col]=='.'){
The SEGV appears here as you access p[N][M], but the indices of p can only go from 0 to N-1 and 0 to M-1 respectively. This loop should probably read:
for (row=0; row < N;++row){ //Here the things get messy
for ( col = 0 ; col < M ;++col){
if(p[row][col]=='.'){
(note change to start at row=0, and row < N not row <= M and similarly for col).
The second problem you have is to do with what to do at the edges:
Lines like this:
if (p[row][col-1]=='*' && col > 1)
count=count+1;
should have the col > 1 condition first so they don't evaluate the array element unless the condition is true. Also, as col goes 0..M-1, you want
if ((col > 0) && (p[row][col-1]=='*'))
count=count+1;
Note I've put in some brackets to avoid any ambiguity.
The same applies when looking at the other edges:
if (p[row][col+1]=='*' && col < M)
count=count+1;
should be:
if ((col < M-1) && (p[row][col+1]=='*'))
count=count+1;
That should get you going. But learn to use a debugger.