C Programming – Understanding c-‘0’

c++

I was trying to test one of the K&R function which uses c-'0'. To understand clearly I wrote a two line code as below. My question is why is it printing "1". And what does the "numeric value" actually mean in this context. Thanks!

char c = 'a';
printf("%c",c-'0');

Best Answer

c - '0' only has a definite specific value when c is a digit ('0', '1', ..., or '9').

When c is '0', '0' - '0' is 0 because they are equal when c is '1', '1' - '0' is 1 because '1' immediately follows '0' in any character set any C implementation choses to use. The same for '2' and the other digits: '9' - '0' has a value of 9.

And you really shouldn't print a value with the "%c" format specifier.

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C Programming – What is ‘{0}’?

This is just an initializer list for an array. So it's very like the normal syntax:

char buf[5] = { 1, 2, 3, 4, 5 };

However, the C standard states that if you don't provide enough elements in your initializer list, it will default-initialize the rest of them. So in your code, all elements of buf will end up initialized to 0.

printf doesn't display anything because buf is effectively a zero-length string.

Best Answer

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C Programming – What is ‘{0}’?

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