Why you mustn't write scanf(“%.2lf”, &a) in C?

Question

My friend have just started learning programming. He showed me his code and asked why it return some weird number. After taking a look at it, I saw that he was using sca

Answer 1

The C standard specifies that scanf conversion specifiers begin with %, and the POSIX standard specifies they begin with either % or %n$.

Neither the C standard nor the POSIX standard allows for a . in the conversion specifier, so this character is invalid.

You may have a decimal integer in your conversion specifier before the type specifier, but it specifies the maximum field width of the type. This means that scanf will read at most 2 characters before stopping when passed %2lf.

Additionally, lf specifies that the value should be a double, so a should be of type double.