Two-dimensional arrangement practice

Question

First, sorry for my poor language. I'm using VC++ Express myself.

Now I'm studying about arrangements. The book gave me a project like so:

• Make a 5x5 matrix.
• Each column is for subjects (4 of them)
• Each row is for students (same, 4 of them)
• Each cell saves a score.
• At the end of each row/column, sum the row/column.

And this is my answer program:

int main(void)
{
int arr[5][5];
int i,j;

while(1)
{
 printf("student: 1.Jim,2.Jombi,3.Joly,4.Moran if you done, type 0\n");
 scanf("%d", &i);

 if(i=0)
  break;

 printf("subject: 1.english,2.spanish,3.poolish,4.flash\n");
 scanf("%d", &j);

 printf("insult score!\n");
 scanf("%d", arr[i-1][j-1]);//insulting score
}

for(i=0;i<4;i++)//initialization of sum parts
{
 arr[i][4]=0;
 arr[4][i]=0;
}

for(i=0;i<4;i++)
 for(j=0;j<4;j++)
  arr[4][i]+=arr[j][i];

for(i=0;i<4;i++)
 for(j=0;j<4;j++)
  arr[i][4]+=arr[i][j];


for(i=0;i<5;i++)
{
 for(j=0;j<5;j++)
  printf("%d ",arr[i][j]);//printing result
 printf("\n");
}
return 0;
}

I completely don't know why this code doesn't work. Even when I tried only "while" part, it didn't work also. Why is this?

Answer 1

if(i=0)

I don't know if this is the source of your problem, but this should be:

if(i==0)

Answer 2

The index in your last for loop is one-off. Should be 4, you use 5.

Answer 3

A couple of points:

• You're missing the & (address-of) operator in your scanf() call, so you'll pass the integer in the array instead.
• Consider just doing a simple memset(arr, 0, sizeof arr); before the input loop to make sure the array is clear, rather than the nested fors to zero out just the sums. Safer, shorter, easier to understand.
• Add instrumentation, such as printing the matrix after the input step, to make sure it looks alright.

Answer 4

As has been pointed, you have an if wrong

if (i == 0)
/*   ^^^ */

And you have a scanf wrong too

scanf("%d", &arr[i-1][j-1]);
/*         ^^^ */

And you really, Really, REALLY shoud initialize the array with something (possibly zeroes)

int arr[5][5] = {0};