Structure of C Program

The Structure of C program is fundamental to understand how to write code effectively. This section will outline the basic syntax of a C program, including its structure, syntax, and examples :

Table of Contents

What is the Structure of C ?

The Structure of a C program refers to the arrangement of various elements that make up the program, including preprocessor directives, function declarations, variable declarations, and statements. Each part plays a specific role in the program’s functionality and overall organization.

Syntax of C

The syntax of C programming refers to the set of rules that defines the combinations of symbols and keywords that are used in a C Program. Understanding the syntax is crucial for writing valid and functional C codes.

Example of Syntax :
#include <stdio.h> // Preprocessor directive

// Main function - execution starts here
int main() {
    // Variable declarations
    data_type variable_name;

    // Statements
    statement1;
    statement2;
    // ...

    return value; // Return statement
}
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Key Elements of C Syntax

  • Preprocessor Directives:
    • Syntax: #include <header_file.h>
    • Used to include standard libraries or other header files before the compilation of the program.
  • Function Declarations:
    • Syntax: return_type function_name(parameter_list);
    • Declares a function, specifying its return type and parameters (if any).
  • Main Function:
    • Syntax: int main() { ... }
    • The entry point of a C program where execution begins.
  • Variable Declarations:
    • Syntax: data_type variable_name;
    • Declares a variable of a specified data type.
  • Statements:
    • Syntax: statement1; statement2;
    • Executable instructions that must end with a semicolon (;).
  • Comments:
    • Single-line comment: // This is a single-line comment
    • Multi-line comment: /* This is a multi-line comment */
    • Comments are used to document code and are ignored by the compiler.
  • Data Types:
    • Common data types include:
      • int: for integers
      • float: for floating-point numbers
      • double: for double-precision floating-point numbers
      • char: for characters
  • Operators:
    • Arithmetic operators: +, -, *, /, %
    • Relational operators: ==, !=, >, <, >=, <=
    • Logical operators: &&, ||, !

We’ll discuss about them in detail one by one in our upcoming sections.

Some more Examples of C

Here are some basic C Programs which are taught in College :

1. Adding Two Numbers

This program takes two integers as input and prints their sum.

#include <stdio.h>

int main() {
    int num1, num2, sum;

    // Input two numbers
    printf("Enter first number: ");
    scanf("%d", &num1);
    printf("Enter second number: ");
    scanf("%d", &num2);

    // Calculate sum
    sum = num1 + num2;

    // Display the result
    printf("Sum: %d\n", sum);

    return 0;
}
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2. Printing Numbers from 1 to 10

This program prints the numbers from 1 to 10 using a loop.

#include <stdio.h>

int main() {
    int i;

    // Print numbers from 1 to 10
    printf("Numbers from 1 to 10:\n");
    for (i = 1; i <= 10; i++) {
        printf("%d\n", i);
    }

    return 0;
}
C

3. Finding the Largest of Three Numbers

This program takes three numbers as input and determines the largest among them.

#include <stdio.h>

int main() {
    int num1, num2, num3;

    // Input three numbers
    printf("Enter three numbers:\n");
    scanf("%d %d %d", &num1, &num2, &num3);

    // Determine the largest number
    if (num1 >= num2 && num1 >= num3) {
        printf("Largest number: %d\n", num1);
    } else if (num2 >= num1 && num2 >= num3) {
        printf("Largest number: %d\n", num2);
    } else {
        printf("Largest number: %d\n", num3);
    }

    return 0;
}
C

4. Calculating the Factorial of a Number

This program calculates the factorial of a given number using a loop.

#include <stdio.h>

int main() {
    int num, i;
    unsigned long long factorial = 1; // Use long long for larger numbers

    // Input a number
    printf("Enter a positive integer: ");
    scanf("%d", &num);

    // Calculate factorial
    for (i = 1; i <= num; i++) {
        factorial *= i;
    }

    // Display the result
    printf("Factorial of %d = %llu\n", num, factorial);

    return 0;
}
C

5. Reversing a Number

This program reverses a given integer.

#include <stdio.h>

int main() {
    int num, reversedNum = 0, remainder;

    // Input a number
    printf("Enter an integer: ");
    scanf("%d", &num);

    // Reverse the number
    while (num != 0) {
        remainder = num % 10; // Get the last digit
        reversedNum = reversedNum * 10 + remainder; // Build the reversed number
        num /= 10; // Remove the last digit
    }

    // Display the result
    printf("Reversed Number: %d\n", reversedNum);

    return 0;
}
C

These basic C programs introduce fundamental programming concepts such as input/output, loops, conditionals, and arithmetic operations. As you practice these programs, you’ll gain a better understanding of how to structure and write C code effectively.

Understanding the syntax of C is essential for writing valid programs. By adhering to these rules and conventions, programmers can create effective and efficient code. In upcoming posts, we will explore specific features of C, including control structures, data types, and functions.

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