casting - C cast literal char '0' to int 0 (zero), how?

Question

How would I go to cast/convert literal char '0' to int 0?

i.e.:

char string[] = "0101";
char ch = string[0];
x = magic(ch);
if (x)
    printf("int zero")

Answer 1

ch = 0;

Now, if you want to convert any digit-character to its numeric equivalent, you'd need something like:

ch = ch - '0';