Variable Definition in C
A variable definition tells the compiler where and how much storage to create for the variable. A variable definition specifies a data type and contains a list of one or more variables of that type as follows −
type variable_list;
Here, type must be a valid C data type including char, w_char, int, float, double, bool, or any user-defined object; and variable_list may consist of one or more identifier names separated by commas. Some valid declarations are shown here −
int i, j, k;
char c, ch;
float f, salary;
double d;
This is all about basics which is required to solve your question.
All the 4 declarations that u have given is perfect But One thing when u go print tha value of PI , u have to use proper format specifier
like: for int - u have to use '%d'
for float - u have to use "%f"
for double - "%d"
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#define PI 3.14: this is macro definition i think. So when we want to print 3.14 in place of PI then we have to use format specifier " %f "...