Definition:
A variable in C is a name given to a memory location that stores data. The value of a variable can change during program execution.
Syntax:
data_type variable_name = value;
Rules for Naming Variables:
1. Can contain letters (A-Z, a-z), digits (0-9), and underscore (_).
2. Must start with a letter or an underscore.
3. Cannot be a C keyword.
4. Case-sensitive (age and Age are different).
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Types of Variables in C
1. Integer Variable (int)
Stores whole numbers.
Example:
#include <stdio.h>
int main() {
int a = 10;
printf("Value of a: %d", a);
return 0;
}
Output:
Value of a: 10
2. Floating-point Variable (float, double)
Stores decimal numbers.
Example:
#include <stdio.h>
int main() {
float pi = 3.14;
double largeValue = 3.1415926535;
printf("Float: %f\n", pi);
printf("Double: %lf", largeValue);
return 0;
}
Output:
Float: 3.140000
Double: 3.141593
3. Character Variable (char)
Stores a single character.
Example:
#include <stdio.h>
int main() {
char grade = 'A';
printf("Grade: %c", grade);
return 0;
}
Output:
Grade: A
4. String Variable (char array)
Stores a sequence of characters.
Example:
#include <stdio.h>
int main() {
char name[] = "John";
printf("Name: %s", name);
return 0;
}
Output:
Name: John
5. Boolean Variable (_Bool) (C99 and later)
Stores 1 (true) or 0 (false).
Example:
#include <stdio.h>
#include <stdbool.h>
int main() {
bool isCodingFun = 1; // true
printf("Is coding fun? %d", isCodingFun);
return 0;
}
Output:
Is coding fun? 1
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Types of Variable Scope in C
1. Local Variable: Declared inside a function, accessible only within that function.
2. Global Variable: Declared outside all functions, accessible throughout the program.
3. Static Variable: Retains its value between function calls.
4. Extern Variable: Declared in one file but accessible in another file.
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Example with Local, Global, and Static Variables
#include <stdio.h>
int globalVar = 20; // Global variable
void demoFunction() {
static int staticVar = 5; // Static variable
int localVar = 10; // Local variable
printf("Local: %d, Static: %d, Global: %d\n", localVar, staticVar, globalVar);
staticVar++;
}
int main() {
demoFunction();
demoFunction();
return 0;
}
Output:
Local: 10, Static: 5, Global: 20
Local: 10, Static: 6, Global: 20
---
Conclusion
Variables store data and can change values.
Different data types store different kinds of values.
Scope determines variable accessibility.
Static variables retain their values across function calls.
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