So, here's my C code. While I was toying with my code in order to learn the format specifiers, especially %c:
#include <stdio.h>
void main()
{
double a = 0.21;
printf("%c", a);
}
I happened to encounter that even if I pass a floating value as an argument in printf() function for the format specifier %c, the compiler (my compiler is gcc) somehow converts the value 0.21 into decimal value 223 which corresponds to ASCII character ß.
For a = 0.22 the output is: ) whose decimal value in ASCII table is 29
I ran the code on both VS code and CLion IDEs, but the results were same. Now it is making me scratch my head for days and I can't figure it out.
I want to know how the values 0.21 and 0.22 are getting converted into the decimal 223 and 29 or how they correspond to the ASCII 223 and 29 i.e. ß and ) respectively.
Since the value 0.21, 0.22 does not corresponds to any of the ASCII, I was expecting the program to print nothing.
But based on the output I thought that this might have something to do with the binaries.
As 0.21 in binary is 0.00110101110000101000111101011100...
& 223 is 11011111
and 0.22 in binary is 0.00111000010100011110101110000101...
& 29 is 00011101
And I could not find any conversion pattern.
Passing a float (which is automatically converted to a double in this case) for a %c has undefined behavior. printf looks for the argument where you program would have passed it if its type was int or a smaller type that promotes to int and uses that value. In your case the value happens to be 223 or 29 depending on circumstances and it could be something else on a different CPU, or after any unrelated change in the program or even just at a different time or place... The behavior is undefined, you could also get no output or a program crash (unlikely but not impossible).
Use compiler warnings to try and detect such problems (gcc -Wall -Wextra -Werror) and avoid scratching your head trying to make sense of undefined behavior.