Why might the values in an array declared in C have values that were not set explicitly?

Well, the automatic variables in C are not initialized at all by default. The only exception to this - if you are initializing at least one element of an array, the rest of it gets initialized to zero. The same zeroing effect cannot be got by assignment which is what you are doing down the lane. Hence, the garbage values, which can be 0 by coincidence! :) Also, note that automatic variables are just local variables within a block of a function, but that doesn't mean the reverse should be true. Heard of static variables declared and defined within a function? Yeah, the desirable effect of zeroing down all the array elements by not even initializing one of them is possible having a static array declared either within any function or outside of all the functions(in this case you wouldn't need the keyword static which would otherwise become a file-scope variable). And these will occupy different segment in memory unlike the automatic ones being on stack. Here is an ex: int c[ 40 ]; // Zeroed down by default. int main(void) { int a[ 20 ] = { 20 }; // Zeros down rest. static int b[ 30 ]; // Zeroed down by default. int d[ 50 ]; // Contains garbage by default. d[ 0 ] = 12; // Still the rest of the array d will be having garbage values // as the assignment operation in C is not meant for zeroing // down the rest of the elements of the array - it's just the way // "C" is designed. return 0; } Hope this helps. Cheers, Raghavan