Computers do not understand English language. It can only understand machine code, a binary stream of 1s and 0s.
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To learn any language we need to first learn alphabets, then we learn to write sentences and then to write paragraphs. Similarly, in learning C programming language, we first learn about the Character Set(Alphabets, Digits, Special Symbols), next we learn words(keywords, variables, constants), and then we learn statements(C programming instructions), and then we write C programs.
Keywords, Identifiers And Literals: C
Every word in a C program is classified as either a keyword or an identifier. All keywords have fixed meanings predefined in the language and these meanings can not be changed.
In programming languages, constants are usually called as literals and variables are called as identifiers.
As name suggests, a constant is an entity whose value doesn’t change during the course of program execution. A variable, on the other hand, is an entity whose value may change during the course of program execution.
C Constants can be divided into 2 categories.
1. Primary Constants.
2. Secondary Constants.
Primary Constants are further divided into Integer Constants, Real Constants and Character constants.
Keyword for Integer is int and the format specifier is %d.
Keyword for Real is float or double and the format specifier is %f.
Keyword for Character is char and the format specifier is %c.
#include < stdio.h >
int main()
{
const int a = 5;
a = a + 1;
printf("Value of a is %d", a);
}
Output:
error: Assignment of read-only variable ‘a’.
a is a constant variable and thus its value can not be changed through the course of program execution.
#include < stdio.h >
int main()
{
int a = 5;
a = a + 1;
printf("Value of a is %d", a);
}
Output:
Value of a is 6
Note: Literals are constant values and not constant variables.