How to initialize an array to something in C without a loop?

Besides the initialization syntax, you can always memset(arr, 0, sizeof(int)*10*10)

The quick-n-dirty solution:

int arr[10][10] = { 0 };

If you initialise any element of the array, C will default-initialise any element that you don't explicitly specify. So the above code initialises the first element to zero, and C sets all the other elements to zero.