Fundamental Concepts of C Programming: Short Answer Questions (5 Marks)

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Fundamental Concepts of C Programming: Short Answer Questions (5 Marks)

This blog post provides detailed answers to common short-answer questions in C programming. Whether you're a student preparing for exams or a beginner looking to strengthen your fundamentals, these explanations and examples will help you understand key concepts in C.

1. Define “constant”, “identifier” and “keyword” in C.

• Constant: A constant in C is a value that remains unchanged throughout the execution of a program. Constants can be defined using the #define directive or as const variables.
  Example:

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  #define PI 3.14   // PI is a constant value
  const int MAX = 100;  // MAX is a constant variable
  

• Identifier: An identifier is the name given to variables, functions, arrays, or any other user-defined item in a C program. An identifier must begin with a letter (uppercase or lowercase) or an underscore (_), followed by letters, digits, or underscores. It cannot be a keyword.
  Example:

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  int age; // 'age' is an identifier
  

• Keyword: A keyword is a reserved word that has a predefined meaning in C and cannot be used as an identifier. C has a set of keywords such as int, float, if, while, etc.
  Example:

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  int sum = 10; // 'int' is a keyword
  

2. What is a variable? List the major data types used in a C program.

A variable in C is a memory location where data can be stored, modified, and retrieved. Each variable is associated with a data type, which defines the kind of data it can store.

Major data types in C:

• int: Used for storing integer values.
  Example:

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  int age = 25;
  

• float: Used for storing single-precision floating-point numbers.
  Example:

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  float temperature = 36.6;
  

• char: Used for storing a single character.
  Example:

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  char grade = 'A';
  

• double: Used for storing double-precision floating-point numbers (greater precision than float).
  Example:

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  double pi = 3.14159;
  

• void: Represents an empty type. Used for functions that do not return any value.

3. What is a structure in a C program? Explain.

A structure is a user-defined data type in C that allows grouping different data types into a single unit. A structure can contain variables of different types, which are called members or fields of the structure.

Example:

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struct Student {
    char name[50];
    int roll;
    float marks;
};

Here, the structure Student has three members: name, roll, and marks, which can hold different types of data.

To use a structure:

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struct Student student1;
student1.roll = 101;
strcpy(student1.name, "John");
student1.marks = 85.5;

4. List out the different types of operators in C. Describe the logical operator with an example.

Types of operators in C:

• Arithmetic Operators: +, -, *, /, % (Used to perform mathematical operations)
• Relational Operators: ==, !=, <, >, <=, >= (Used to compare two values)
• Logical Operators: && (AND), || (OR), ! (NOT) (Used to perform logical operations)
• Bitwise Operators: &, |, ^, ~, <<, >> (Used to perform bit-level operations)
• Assignment Operators: =, +=, -=, *=, /=, %= (Used to assign values to variables)
• Increment/Decrement Operators: ++, -- (Used to increase or decrease a variable’s value)

Logical Operator Example:

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int a = 5, b = 10;
if (a > 0 && b > 0) {
    printf("Both are positive numbers");
}

Here, the && operator checks if both conditions are true.

5. Define a pointer in C with an example.

A pointer is a variable that stores the memory address of another variable. Pointers are powerful tools in C, used for dynamic memory allocation, array handling, and function arguments.

Example:

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int x = 10;
int *ptr = &x;  // pointer ptr stores the address of variable x
printf("Value of x: %d\n", *ptr); // Dereferencing the pointer gives the value of x

Here, &x gives the memory address of x, and *ptr dereferences the pointer to access the value of x.

6. Describe the different modes of file handling in C.

In C, file handling allows reading and writing data to files. The file must be opened in one of the following modes:

• "r": Open for reading. If the file doesn’t exist, it returns NULL.
• "w": Open for writing. If the file doesn’t exist, it creates a new file. If the file exists, it truncates the file.
• "a": Open for appending. If the file doesn’t exist, it creates a new file. If the file exists, data is written at the end.
• "r+": Open for both reading and writing.
• "w+": Open for both reading and writing. Creates a new file if it doesn’t exist, truncates it if it does.
• "a+": Open for both reading and appending.

7. Explain the file handling concept in C.

File handling in C allows programs to read and write data from or to a file. It involves three basic operations:

1. Opening a file using the fopen() function.
2. Performing operations like reading and writing using functions such as fprintf(), fscanf(), fputs(), fgets(), etc.
3. Closing the file using the fclose() function to release the resources.

Example:

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FILE *fp;
fp = fopen("file.txt", "w");
fprintf(fp, "Hello, World!");
fclose(fp);

8. Differentiate between an array and a structure with an example.

• Array: An array is a collection of elements of the same data type stored in contiguous memory locations. Example:

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

• Structure: A structure is a user-defined data type that can store variables of different types.
  Example:

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  struct Student {
      char name[50];
      int roll;
      float marks;
  };
  

9. Explain the array and structure with examples.

• Array Example:

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  int arr[3] = {10, 20, 30};
  printf("%d", arr[1]); // Output: 20
  

• Structure Example:

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  struct Student {
      char name[50];
      int roll;
      float marks;
  };
  
  struct Student student1;
  student1.roll = 101;
  strcpy(student1.name, "John");
  student1.marks = 85.5;
  

10. What is a function? List out the advantages of functions.

A function is a block of code that performs a specific task. Functions help in organizing and modularizing the code.

Advantages of Functions:

1. Code Reusability: Functions allow code to be reused multiple times.
2. Modular Programming: Functions break the code into smaller modules, making it easier to understand and maintain.
3. Easier Debugging: Errors can be isolated and fixed in specific functions.
4. Improved Readability: Functions help in organizing the code logically.

11. Describe fscanf and fprintf functions.

• fscanf(FILE *fp, format, variables): Reads data from a file based on the specified format.
  Example:

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  FILE *fp = fopen("data.txt", "r");
  int age;
  fscanf(fp, "%d", &age);  // Reads an integer from the file
  fclose(fp);
  

• fprintf(FILE *fp, format, variables): Writes data to a file based on the specified format.
  Example:

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  FILE *fp = fopen("output.txt", "w");
  fprintf(fp, "Age: %d", 25);  // Writes the integer to the file
  fclose(fp);
  

12. Differentiate between a structure and a union.

• Structure: A structure allocates memory for each member independently, allowing each member to hold different data types.
• Union: A union allocates memory equal to the size of its largest member, and all members share the same memory space.

Example:

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union Data { int i; float f; };
struct Data { int i; float f; };

In a structure, both i and f can hold different values at the same time, whereas in a union, only one of them can hold a value at any given time.