c - how can u assign an integer value to a char datatype? -

in below code how can char data type assigned integer variable (as in char data type alphabets written in single quote) , while printing char data type using %d subscript instead of using %c ?

#include <stdio.h>      int main()     {         char = 30, b = 40, c = 10;         char d = (a * b) / c;//a char value storing integer value ?how ?         printf ("%d ", d);          return 0;     } 

how can char data type storing integer value

chars small integers can hold values in range [-128;127].
(on systems may [0;255]. on rare platforms can have size, never see these cases.)

character literals '0' codes of corresponding symbols. example, '0' equal 48.
(on encodings. values rare.)

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why %d works char? because when pass chars , shorts ... function argument, automatically converted ints.
, printf declared printf(const char *, ...);.