Learn C: Basics

Basic Syntax and Structure

C programs are structured into functions, with the main function serving as the entry point. Each C program must have a main function.

Structure of a C Program

#include <stdio.h>

int main() {
    // Your code here
    return 0;
}

This simple template includes:

• #include <stdio.h> - This preprocessor directive includes the standard input-output header file, which is necessary for functions like printf.
• int main() - The main function where program execution begins.
• return 0; - This statement indicates that the program ended successfully.

Variables and Data Types

In C, variables are used to store data. You must declare a variable before using it, specifying its data type.

Common Data Types

• int - For integer values.
• float - For floating-point numbers (decimals).
• double - For double-precision floating-point numbers.
• char - For single characters.

Example of variable declaration:

int age;
float salary;
char grade;

Operators

C provides several operators to perform arithmetic, comparison, and logical operations:

• Arithmetic Operators: +, -, *, /, %
• Comparison Operators: ==, !=, >, <, >=, <=
• Logical Operators: && (logical AND), || (logical OR), ! (logical NOT)

Example of using operators:

int a = 10;
int b = 20;
int sum = a + b; // Arithmetic operator
if (a > b) {
    printf("a is greater than b");
} else {
    printf("a is not greater than b");
}

Control Flow Statements

C provides several control flow statements to make decisions and repeat tasks:

• if - Executes a block of code if a condition is true.
• else - Executes a block of code if the condition in the if statement is false.
• for - Loops through a block of code a specified number of times.
• while - Loops through a block of code while a condition is true.
• do-while - Loops through a block of code at least once and then repeats as long as a condition is true.

Example of Control Flow

// if-else statement
int number = 10;
if (number % 2 == 0) {
    printf("Number is even");
} else {
    printf("Number is odd");
}

// for loop
for (int i = 0; i < 5; i++) {
    printf("%d\n", i);
}

// while loop
int i = 0;
while (i < 5) {
    printf("%d\n", i);
    i++;
}

// do-while loop
int j = 0;
do {
    printf("%d\n", j);
    j++;
} while (j < 5);

Functions

Functions are blocks of code that perform a specific task. They help in breaking down complex programs into smaller, manageable parts.

Defining a Function

return_type function_name(parameters) {
    // body of the function
    return value;
}

Example of a function that adds two numbers:

int add(int a, int b) {
    return a + b;
}

int main() {
    int result = add(5, 3);
    printf("The sum is %d", result);
    return 0;
}

Input and Output

C uses functions from the stdio.h library to handle input and output. The printf function is used for output, while scanf is used for input.

Example of Input and Output

#include <stdio.h>

int main() {
    int age;
    printf("Enter your age: ");
    scanf("%d", &age);
    printf("You are %d years old.\n", age);
    return 0;
}

Arrays

Arrays are used to store multiple values of the same type in a single variable. They are indexed starting from 0.

Example of an Array

int numbers[5] = {1, 2, 3, 4, 5};

for (int i = 0; i < 5; i++) {
    printf("%d\n", numbers[i]);
}

Conclusion

Understanding the basics of C programming is essential for building a solid foundation in software development. With knowledge of variables, data types, operators, control flow, functions, and arrays, you're well on your way to writing effective C programs.

In the next section, we will cover more advanced topics such as pointers, data structures, and memory management.