Pins confusion in projects

is it that we can not use any other pin other than A0 pin for the ldr project ?
is it that A0 pin can not be used to connect the other end of the resistor in led project?

A0 is the pin to be used if you want to read analog signals. LDR sensor gives analog voltage which varies with light. ADC(Analog - to - Digital Converter) convert this to Digital. So you have to use A0 pin to get proper output.

The circuit is a voltage divider circuit shown in image. So here Z1 = LDR sensor, Z2 = Resistor. Vin = 3.3V, Vout = A0 pin. Thats why the resistor is connected as shown in tutorial

For more info:

We make use of the ‘A0’ pin for LDR project because :
1)the input from the LDR sensor is of analog type and we know that the ‘A0’ pin is used whenever the input is analog type
2) the output of the LDR is supposed to be digital
The resisitor is used to form a voltage divider circuit and hence it is connected to the ‘A0’ pin and the ground