C Programming: Datatypes, Modifiers & Variables

1. Datatypes and Their Properties

A datatype tells the C compiler what kind of data a variable is intended to store.

A datatype determines:

1. The type of data that can be stored.
2. The amount of memory normally required.
3. The operations that can be performed.
4. The range of values that can be represented.

2. Memory and Bytes

Computer memory is commonly measured in bytes. A byte consists of 8 bits.

3. Basic C Datatypes

3.1 int

The int datatype is used to store integer (whole-number) values.

int age = 45;
int marks = 95;
int temperature = -10;

3.2 float

float is used for floating-point numbers, which can contain a fractional part.

float price = 23.45f;
float temperature = 36.5f;

The suffix f indicates that the numeric literal is a float.

3.3 double

double generally provides more precision than float.

double pi = 3.141592653589793;
double distance = 12345.678901;

3.4 char

The char datatype stores a single character. Character constants are written inside single quotes.

char grade = 'A';
char symbol = '$';
char digit = '5';

4. ASCII

ASCII stands for American Standard Code for Information Interchange.

ASCII assigns numeric codes to commonly used characters. Standard ASCII uses values from 0 to 127.

5. Example Using Different Datatypes

#include <stdio.h>

int main(void)
{
    int x = 45;
    float y = 2.34f;
    double z = 48.369;
    char ch = 'A';

    printf("x = %d\n", x);
    printf("y = %f\n", y);
    printf("z = %f\n", z);
    printf("ch = %c\n", ch);

    return 0;
}

Common Format Specifiers

6. sizeof Operator

The sizeof operator is used to determine the amount of memory, in bytes, occupied by a datatype or object.

Syntax:

sizeof(variable)
sizeof(datatype)

Example

#include <stdio.h>

int main(void)
{
    printf("Size of int    = %zu bytes\n", sizeof(int));
    printf("Size of float  = %zu bytes\n", sizeof(float));
    printf("Size of double = %zu bytes\n", sizeof(double));
    printf("Size of char   = %zu byte\n", sizeof(char));

    return 0;
}

7. Datatype Modifiers

C provides modifiers that can be used with certain datatypes to change their range or representation.

The commonly used modifiers are:

They are particularly important when working with integer types.

8. Signed vs Unsigned

signed

A signed integer can represent both positive and negative values.

signed int temperature = -20;
int marks = 90;

int is signed by default unless explicitly declared as unsigned.

unsigned

An unsigned integer represents non-negative values (zero and positive values).

unsigned int count = 100;
unsigned int population = 500000;

For an integer type of a given width, using unsigned generally allows a larger maximum positive value because negative values are not represented.

9. short vs long

short and long can be used to select integer types with different minimum ranges and potentially different sizes.

short int smallNumber;
long int largeNumber;

short smallNumber2;
long largeNumber2;

Checking the Size

#include <stdio.h>

int main(void)
{
    short int x;

    printf("Memory allocated for x = %zu bytes\n", sizeof(x));

    return 0;
}

10. Variables in C

A variable is a named memory location used to store a value that can change during program execution.

Declaration

A variable must be declared before it is used.

int x;

Assignment

A value can then be assigned to the variable.

x = 10;

Complete Example

#include <stdio.h>

int main(void)
{
    printf("C Program\n");

    int x;
    x = 10;

    printf("x = %d\n", x);

    return 0;
}

11. Initialization and Assignment

Giving a variable its first value is called initialization.

int x;
x = 10;       // initialization

After initialization, the variable can be assigned new values.

x = 20;       // reassignment
x = 30;       // reassignment

Example

#include <stdio.h>

int main(void)
{
    int x;

    x = 10;
    printf("x = %d\n", x);

    x = 20;
    printf("x = %d\n", x);

    x = 30;
    printf("x = %d\n", x);

    return 0;
}

12. Declaration with Initialization

A variable can be declared and initialized in the same statement.

int x = 10;

Example

#include <stdio.h>

int main(void)
{
    int x = 10;

    printf("x = %d\n", x);

    return 0;
}

13. Uninitialized Variables

A local variable declared without an initial value does not automatically contain a useful value.

#include <stdio.h>

int main(void)
{
    int x;

    printf("x = %d\n", x);  // Do NOT do this

    return 0;
}

14. const Keyword

The const qualifier can be used when a variable should not be modified through that identifier after initialization.

#include <stdio.h>

int main(void)
{
    const int x = 4;

    printf("x = %d\n", x);

    // x = 12;  // Error

    return 0;
}

15. Redeclaring a Variable

A variable cannot be declared again with the same name in the same scope.

#include <stdio.h>

int main(void)
{
    int x;

    x = 12;
    printf("x = %d\n", x);

    // float x;   // Error: x already declared in this scope

    return 0;
}

16. Declaring Multiple Variables

Multiple variables of the same datatype can be declared in one statement using commas.

int a, b, c;

Assigning the Same Value

#include <stdio.h>

int main(void)
{
    int a, b, c;

    a = b = c = 10;

    printf("a = %d\n", a);
    printf("b = %d\n", b);
    printf("c = %d\n", c);

    return 0;
}

The expression is evaluated from right to left:

c = 10;
b = c;
a = b;

Therefore, all three variables finally contain 10.

17. Assigning Different Values

Multiple variables can also be declared and initialized with different values in one statement.

#include <stdio.h>

int main(void)
{
    int x = 5, y = 10, z = 15;

    printf("x = %d\n", x);
    printf("y = %d\n", y);
    printf("z = %d\n", z);

    return 0;
}

18. Quick Revision

19. Practice Questions

A. Multiple Choice Questions

B. Fill in the Blanks

C. Predict the Output

#include <stdio.h>

int main(void)
{
    int x = 10;

    printf("%d\n", x);

    x = 20;

    printf("%d\n", x);

    return 0;
}

#include <stdio.h>

int main(void)
{
    int a, b, c;

    a = b = c = 25;

    printf("%d %d %d\n", a, b, c);

    return 0;
}

D. Find the Error

#include <stdio.h>

int main(void)
{
    int x = 10;

    float x = 20.5f;

    printf("%d\n", x);

    return 0;
}

E. Programming Exercises

1. Write a C program to declare an int, float, double, and char variable and print their values.
2. Write a program to display the size of char, int, float, and double using sizeof().
3. Write a program that declares three integer variables and assigns the same value to all three using chained assignment.
4. Write a program that declares three integer variables and initializes them with three different values.
5. Write a program demonstrating the difference between int and unsigned int.
6. Write a program using const and try to modify the constant. Observe the compiler error.
7. Write a program that stores a character in a char variable and prints it using %c.
8. Write a program that prints the ASCII value of a character.

20. Challenge Questions

21. Final Summary

Datatypes are fundamental to C programming because they tell the compiler how data should be represented and manipulated. Variables provide named storage locations for that data.

The most commonly used basic datatypes are int, float, double, and char. Modifiers such as signed, unsigned, short, and long can be used with appropriate integer types.

The sizeof operator helps determine the actual size of a datatype or object on the current system. Variables should be initialized before they are used, and const can be used when a value should not be modified through a particular identifier.