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

In C, '0' is an integer whose value represents the digit zero as a character, not the value 0, which would be the null character. Other answers have omitted this, but it's important to note that the C language mandates that the decimal digits have consecutive values, so that if c is a digit, c-'0' is the numeric value of that digit, i.e.

'0'-'0' = 0
'1'-'0' = 1
'2'-'0' = 2
.
.
.
'9'-'0' = 9