Control Structures: if Statements

if / else if / else Statements

The generalized grammar for if / else if / else statements is as follows. First, the series must begin with an if. You cannot begin with else if or else, they must be connected to a starting if. Second, if's and else if's must be followed directly by a set of parenthesis and a conditional expression within the parenthesis. Recall that a conditional expression will yield a zero (representing true) or non-zero (representing false) result or will simply be a literal zero or non-zero value. The if, else if, and else will all be followed by a connected statement block, marked by the open and closing pair of curly brackets. Example syntax for each is given here.

Example structure of an if by itself.

  if (expression) {
    // the statements to execute if the expression is true
  }

Example structure of an if and else combination.

  if (expression) {
    // the statements to execute if the expression is true
  }
  else {
    // the statements to execute if the expression is false
  }

Example structure of an if, else if, else if, and else set.

  if (expression1) {
    // the statements to execute if expression1 is true
  }
  else if (expression2) {
    // the statements to execute if expression2 is true
  }
  // ...
  else if (expressionN) {
    // the statements to execute if expressionN is true
  }
  else {
    // the statements to execute if expression1, expression2, and expression3 are all false
  }

Here is an example code fragment of three independent if statements.

 if (number < 0) {
   printf("Negative");
 }
 if (number < 100) {
   printf("Less than 100");
 }
 if (number >= 100) {
   printf("Greater than or equal to 100");
 }

Here is the same set of conditional expressions included within a single, dependent if and else if combination.

 if (number < 0) {
   printf("Negative");
 }
 else if (number < 100) {
   printf("Less than 100");
 }
 else if (number >= 100) {
   printf("Greater than or equal to 100");
 }