Decision Control Statements in C

Decision Control Statements in C

• Decision control statements are used to execute code based on a condition.
• The three main decision control statements in C are if, if-else, and switch-case.

if Statement

• The if statement evaluates a condition and executes a block of code if the condition is TRUE.
• Conditions are evaluated as either TRUE or FALSE.
• If the expression results in zero, or the direct value is zero, the condition is FALSE.
• Examples:
  • if(10) is TRUE.
  • if(0) is FALSE.
  • if(x + y) is TRUE if (x+y) is not equal to zero.
  • if(num1 > 5) is TRUE if the value of num is greater than 5.

Simple if Statement

• The if statement evaluates the condition.
• If the condition is TRUE, it executes the block of code that follows.
• If the condition is FALSE, it skips the code.
• Syntax:

  if (condition) {
      // Statements to be executed if condition is true
  }
  

• Example:

  if (number < 0) { // Checks if number is negative
      printf("You entered negative number: %d", number);
  }
  

if - else Statement

• The if-else statement evaluates a condition.
• If the condition is TRUE, it executes the first block of code.
• If the condition is FALSE, it executes the second block of code.
• Syntax:

  if (condition) {
      // Statements to be executed if condition is true
  } else {
      // Statements to be executed if condition is false
  }
  

• Example:

  if (number < 0) { // Checks if number is negative
      printf("You entered negative number: %d", number);
  } else {
      printf("You entered zero or positive number: %d", number);
  }
  

Nested if Statement

• A nested if statement is an if-else statement within another if-else statement.
• Syntax:

  if (condition1) {
      if (condition2) {
          // Statements to be executed if condition1 and condition2 are TRUE
      } else {
          // Statements to be executed if condition1 is TRUE and condition2 is FALSE
      }
  } else {
      // Statements to be executed if condition1 is FALSE
  }
  

• Example:

  if (number < 0) { // Checks if number is negative
      printf("You entered negative number: %d", number);
  } else { 
      if (number == 0) { // Checks if number is equal to zero
          printf("You entered zero");
      } else {
          printf("You entered positive number: %d", number);
      }
  }
  

if – else – if Statement (if-else Ladder)

• The if-else-if ladder allows for multiple conditions to be checked.
• Each condition is evaluated sequentially.
• The first condition that is TRUE results in its corresponding code being executed.
• If none of the conditions are TRUE, the code in the final 'else' block is executed.
• Syntax:

  if (condition1) {
          // Statements to be executed if condition1 is TRUE
  } else if (condition2) {
      // Statements to be executed if condition1 is FALSE and condition2 is TRUE
  } else if (condition3) {
      // Statements to be executed if condition1 and condition2 are FALSE, and condition3 is TRUE
  } ... else {
      // Statements to be executed if all conditions are FALSE
  }
  

• Example:

  if(number < 0) { // Checks if number is negative
      printf("You entered negative number: %d", number);
  } else if (number > 0) { // Checks if number is positive
      printf("You entered positive number: %d", number);
  } else { 
      printf("You entered zero");
  }