Getting Started || chapter 1 || let us c

1. What is C? C is a general-purpose, high-level programming language that was developed in the early 1970s by Dennis Ritchie. It is widely used for developing system software, device drivers, and application software. C is a compiled language, which means that it is converted into machine code by a compiler before it is executed.

2. Getting Started with C This section covers the basics of C programming, including the C character set, constants, variables, and keywords.

• The C Character Set: C uses a character set that includes letters, digits, and special symbols. It also includes escape sequences, which allow you to represent special characters in a string.
• Constants, Variables, and Keywords: In C, a constant is a value that does not change during program execution, while a variable is a value that can change. Keywords are reserved words that have special meaning in the C language.

3. Types of C Constants C constants are values that do not change during program execution. There are three types of constants in C:

• Integer Constants: An integer constant is a sequence of digits without a decimal point.
• Real Constants: A real constant is a number with a decimal point.
• Character Constants: A character constant is a single character enclosed in single quotes.

4. Rules for Constructing Constants There are specific rules for constructing integer, real, and character constants in C.

• Rules for Constructing Integer Constants: An integer constant can be a decimal, octal, or hexadecimal number.
• Rules for Constructing Real Constants: A real constant can be a floating-point number or an exponential notation.
• Rules for Constructing Character Constants: A character constant can be a single character or an escape sequence.

5. Types of C Variables In C, a variable is a value that can change during program execution. There are three types of variables in C:

• Local Variables: A local variable is declared inside a function and is accessible only within that function.
• Global Variables: A global variable is declared outside of any function and is accessible throughout the program.
• Static Variables: A static variable is a local variable that retains its value between function calls.

6. Rules for Constructing Variable Names In C, variable names must follow certain rules:

• A variable name must begin with a letter or an underscore.
• A variable name can contain letters, digits, and underscores.
• A variable name cannot be a keyword.

7. C Keywords Keywords are reserved words that have special meaning in the C language. Some examples of keywords in C include "if," "else," "while," "int," "float," "char," and "return."

8. The First C Program The first C program is usually a simple "Hello, World!" program, which prints the message "Hello, World!" to the screen. Here is an example:

c
#include <stdio.h> 
int main() {
printf("Hello, World!"); 
return 0; 
}

9. Compilation and Execution To run a C program, you need to compile it first using a compiler. The compiler will convert the C code into machine code, which can then be executed on the computer. You can use a command-line compiler or an integrated development environment (IDE) to compile and run C programs.

10. Receiving Input In C, you can receive input from the user using the "scanf" function. Here is an example:

c
#include <stdio.h> 
int main() { 
int num;
printf("Enter a number: "); 
scanf("%d", &num);
printf("You entered: %d", num);
return 0;
 }

1. C Instructions Instructions are the building blocks of a C program. There are different types of instructions in C, including:

• Type Declaration Instruction: A type declaration instruction is used to declare a variable and its data type. For example, "int num;" declares an integer variable called "num."

• Arithmetic Instruction: An arithmetic instruction performs mathematical operations on values. For example, "num1 + num2" adds the values of "num1" and "num2."

• Integer and Float Conversions: C automatically converts integers to floats when necessary. However, explicit conversions can also be done using the cast operator. For example, "(float) num" converts the integer variable "num" to a float.

• Hierarchy of Operations: C has a hierarchy of operations, where certain operations are performed before others. For example, multiplication and division are performed before addition and subtraction. To change the order of operations, parentheses can be used.

• Associativity Of Operators: Associativity determines the order in which operations are performed when they have the same priority. For example, the expression "num1 * num2 / num3" is evaluated from left to right.

2. Control Instruction in C Control instructions in C allow you to control the flow of a program. There are different types of control instructions in C, including:

• Conditional Statements: Conditional statements allow you to execute a block of code if a condition is true. The most common conditional statement in C is the "if" statement. For example:

c
if (num > 0) { 
printf("The number is positive.");
 }

• Loop Statements: Loop statements allow you to repeat a block of code multiple times. The most common loop statements in C are the "for" and "while" loops. For example:

css
for (int i = 0; i < 5; i++) { 
 printf("%d ", i); 
}

• Switch Statement: A switch statement allows you to test a variable for multiple values and execute different code for each value. For example:

c
switch (num) { 
case 1: 
    printf("The number is one."); 
    break; 
case 2: 
    printf("The number is two."); 
    break; 
default: 
    printf("The number is neither one nor two.");
 }

3. Summary C is a powerful programming language that is widely used for system software, device drivers, and application software. To get started with C, you need to learn about the C character set, constants, variables, and keywords. You also need to know how to compile and run C programs, receive input, and use instructions and control statements.