How do we use the reserved words in c ?

 You use the reserved words, or keywords, in C by incorporating them directly into your code exactly as they are defined to perform their specific, built-in functions. You cannot use them as names for your own variables, functions, or types.

Here's a breakdown of how you typically use them:

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1. Defining Program Structure and Entry Point 🏠

Keywords define the essential scaffolding of your program.

• int and void in main: You use these to declare the return type of the entry point function.

  C

  int main() { 
      // ... 
      return 0; 
  }
  // 'int' tells the OS the function returns an integer status code.
  // 'void' can also be used if you explicitly return nothing.
  

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2. Declaring Data Types and Variables 📊

Keywords are essential for telling the compiler how to interpret and reserve memory for your data.

• int, float, char: Used when declaring variables.

  C

  int age;          // Declares a variable for an integer
  float salary = 50000.50; // Declares and initializes a float
  char initial = 'J'; // Declares a single character
  

• const: Used to declare a variable whose value cannot be changed after initialization.

  C

  const int MAX_SIZE = 100;
  

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3. Controlling Execution Flow 🚦

Keywords form the backbone of conditional logic and repetition.

• Decision Making:

  C

  if (score >= 90) {
      printf("Grade A\n");
  } else if (score >= 80) {
      printf("Grade B\n");
  } else {
      printf("Grade C\n");
  }
  

• Loops:

  C

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

• Breaking Out:

  C

  while (isRunning) {
      // ... code ...
      if (error) {
          break; // 'break' keyword immediately exits the loop
      }
  }
  

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4. Defining Functions and Scopes 🧩

Keywords help define what a function does and what scope its variables have.

• return: Used inside a function to send a value back to the caller (or end execution).

  C

  int add(int a, int b) {
      return a + b; // Sends the sum back
  }
  

• Storage Class Keywords: Control the scope and lifetime of variables.

  C

  static int counter = 0; // 'static' ensures 'counter' retains its value between function calls
  

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🛑 The Golden Rule: Cannot Be Reused

The most important thing to remember is that you cannot use them for anything else. For example, you cannot do this:

C

// ILLEGAL USAGE: Keywords cannot be identifiers
int float = 5.5;      // ERROR: 'float' is a keyword
void if() { ... }     // ERROR: 'if' is a keyword

Since keywords define the structure of the language, a simple diagram illustrating the control flow keywords might help solidify how they guide the program's execution path.

Would you like to see the full list of the 32 standard C keywords?