Variables & Data Types in C

Declaration

• We cannot declare a variable without specifying its data type.
• The data type of a variable depends on what we want to store in the variable and how much space we want it to hold.
• The syntax for declaring a variable is simple:
• data_type    variable_name;
  or
  data_type variable_name = value;

Rules for defining a variable in C

• Can contain alphabets, digits, and underscore (_)
• A variable name can start with an alphabet and underscore only
• Can't start with a digit
• No whitespace & reserved keywords is allowed
• Valid variable names: int harry, float harry123, char _harry34
• Invalid variable names: $harry, int 77harry, char long;

Data Types in C

• Basic Data Type: int, char, float, double
• Derived Data Type: array, pointer, structure, union
• Enumeration Data Type: enum
• Void Data Type: void

Data Types: Size (32-bit architecture)

                        

                                #include <stdio.h>
                                int main() {
                                    printf("%lu\n", sizeof(int));
                                    printf("%lu\n", sizeof(char));
                                    printf("%lu\n", sizeof(long));
                                    // 'lu' is used for unsigned long
                                    return 0;
                                }