CODEWITHSUNDEEP
c
newbee14
newbee14

Reputation: 1

strange behaviour when printing a float and then an Array

I try to print out two arrays with the following function using XCode 6.1.1:

for (int j=0; j<4; j++) {
    for (int k=0; k<4; k++) {
        printf("%2d ", Lattice[0][j+N*k]);
    }
    printf("        ");
    for (int k=0; k<4; k++) {
        printf("%2d ", Lattice[1][j+N*k]);
    }
    printf("\n");
}
printf("\n");

Everything works fine when calling the function, as long as I don't print out a float before. When printing an int, there's no problem. So it's a little strange, right? I'm initializing the array like this:

int **Lattice =  (int**)malloc(2*sizeof(int*));
if (Lattice == NULL) return NULL;

for (int i=0; i<2; i++){
    Lattice[i] =  (int *)malloc(2*sizeof(int));
    if (Lattice[i] == NULL) {
        for (int n=0; n<i; n++)
            free(Lattice[n]);
        free(Lattice);
        return NULL;
    }
    else{
        for (int j=0; j<N; j++) {
            for (int k=0; k<M; k++) {
                Lattice[i][j+N*k] = 0;
            }
        }
    }
}
return Lattice;

Too bad, I can't upload an image of the output.

The matrices should show only zeros, but with the float there will be big numbers in some entries which i can't explain.

I'm grateful for any hints. Thank you.

Upvotes: 0

Views: 82

Answers (1)

Jonathan Mee
Jonathan Mee

Reputation: 38909

So your code has some pretty serious problems.

Lattice[0] and Lattice[1] need to have dimensions 4x4 for your printing block of code to make any sense. Incidentally this means N and M need to equal 4 as well or you need to change your printing for loop conditions to j < N and k < M respectively.

Your malloc needs to allocate space for that as well, so: Lattice[i] = (int *)malloc(N * M * sizeof(int));

This should cause your loops to work correctly, but you do not have floats anywhere in your code. You cannot use printf to print an int as a float. The value will not be promoted. It will simply be treated as a float.

Upvotes: 1

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