I am assuming that for the first example, you want to set the PWM duty cycle with two push buttons, one to increase the duty cycle and one to decrease it. See the attached example.

For the second example, you can just A/D convert the input, to get a value between 0 and 1023, then divide that by 10, to get a value between 0 and 102, then clamp it to 100 if it's more than 100 (using a greater than or less than op). The resulting value, between 0 and 100, can be specified as the PWM duty cycle.