C Language | Introduction to C | Variables and Data Types

Variables store values temporarily so that a program can reuse input and calculation results.

Declaring and Initializing Variables

A variable names a storage area in memory. The compiler maps the identifier to an address and allocates space according to its type.

type variable1, variable2, ...;

Identifiers may contain letters, digits, and underscores, but cannot begin with a digit or use a reserved keyword. C identifiers are case-sensitive.

Basic type specifiers

Exact sizes other than char depend on the implementation. Use the compiler documentation or sizeof when a size matters.

Assign a value with =, or initialize it during declaration.

int iVariable1 , iVariable2;
iVariable1 = 10;

int iVariable3 = 100;

An uninitialized local variable has an indeterminate value.

Code 1

#include <stdio.h>

int main() {
 int iVariable1 = 10 , iVariable2;
 iVariable2 = 100;
 return 0;
}

Format Specifiers

printf() uses format specifiers that begin with %.

Code 2

#include <stdio.h>

int main() {
 int iVariable = 10;
 printf("iVariable = %d\n" , iVariable);
 return 0;
}

Combining Type Specifiers

Additional specifiers adjust a type’s range or characteristics.

Use signed for signed values and unsigned for values that do not need a negative range.

Code 3

#include <stdio.h>

int main() {
 signed char chVariable = -1;
 unsigned char uchVariable = 255;
 printf("chVariable = %d\nuchVariable = %d\n" , chVariable , uchVariable);
 return 0;
}

Unsigned integer conversion is defined modulo the type’s range. Conversions to signed types outside their representable range depend on the implementation.