How convert a character to integer

Question

Suppose if I have a character let's say char a ='9' and I need to convert it into interger value 9 .How can I do that?.I have tried using inbuilt function atoi().But it is giving error saying you can only pass constant pointer as a arugument.

'90' is not a valid char. See en.cppreference.com/w/cpp/language/character_literal. — R Sahu
– R Sahu, Commented Apr 11, 2019 at 2:36

Faruk Hossain · Accepted Answer · 2019-04-11 02:46:40Z

4

It is simple. just subtract '0' from that character.

char a = '9'; int value = a - '0'; // value = 9.

because ascii value of '9' is 57 and '0' is 48.

So actually it becomes

int value = 57 - 48;

That is value = 9.

answered Apr 11, 2019 at 2:46

Faruk Hossain

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1 Comment

Pete Becker Over a year ago

It’s not just because ASCII. The C and C++ language definitions require that the encodings for the characters ’0’ .. ‘9’ be contiguous and increasing. So ch - ‘0’ works for every character encoding.

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