Access violation writing location 0x00000000. reading int from keyboard

Question

I am trying to read the input from a keyboard which i will use to create a set of multiplications. If i hardcode the integer to use then the program works fine however when

Answer 1

Change

scanf("%d", multiple);

to

scanf("%d", &multiple);

Answer 2

scanf("%d", multiple);

should be:

scanf("%d", & multiple);

In other words, you need to give scanf a pointer to the thing you want to read into. This is a classic mistake in the use of scanf(), and one everyone makes from time to time, so remember this for the next time you make it :-)

Answer 3

You are not passing the address of variable for multiple to store the result from scanf hence the requirement for scanf("%d", &multiple);.

This is telling the runtime, to read an integer and place it into the address-of variable, hence & must be used. Without it, you got a runtime error as you are passing the value of the variable but the runtime does not know what to do with it.

In a nut-shell, an address-of variable is indicated by &.

Hope this helps, Best regards, Tom.

Answer 4

Just to explain why this happened (as Neil already explained what was causing it), scanf was expecting an address to write to. When you passed in the value of 'multiple', it was interpreted as an address, specifically address 0 as that was the value at the time.

The reason for this is so that scanf can set the value of your variable to the value of the input. If you do not pass a pointer you are passing a copy of the value of the variable. When you pass a pointer you are passing a copy of the value of the pointer, so as long as scanf writes to that same memory address it can change the variable's value.

Answer 5

scanf expects a pointer to the variable to set.

The correct form is

scanf("%d", &multiple);