What's the real use of using n[c-'0']?

Question

I\'m a novice in C and I came across the code like this :

int n[10];
if(c>=\'0\' && c<=\'9\')
++n[c-\'0\']

In if

Answer 1

This allows to use a char as an index of an array. For example you could define a string "012345", probably read from an external file, and compute for each character c-'0', which will give the integers 0, 1, 2, 3, 4, and 5 respectively.