Conditionals

A conditional in C can be written using if, else-if, else, ternary operators, and switch statements.

An if statement tests an expression and executes code based on its truth.

if (x == 3) {
  printf("x is 3!");
}

An else-if statement tests an expression and must come after an existing if or else-if.

if (x > 3) {
  printf("x is greater than 3");
} else if (x < 3) {
  printf("x is less than 3");
}

An else statement is accessed when all preceding if and/or else-if statements return false.

if (x > 3) {
  printf("x is greater than 3");
} else if (x < 3) {
  printf("x is less than 3");
} else {
  printf("x equals 3");
}

A dangling else statement results when it’s ambiguous which conditional the else statement is attached to.

A ternary operator is a condensed if-else statement.

min = a < b ? a : b; // This is the same as the if-else below

if (a < b) {
  min = a;
} else {
  min = b;
}

A switch statement is a condensed series of cascading else statements. It tests a value and compares it against multiple cases.

switch (grade) {
  case 9:
    printf("Freshman\n");
    break;
  case 10:
    printf("Sophomore\n");
    break;
  case 11:
    printf("Junior\n");
    break;
  case 12:
    printf("Senior\n");
    break;
  default:
    printf("Invalid\n");
    break;
}

A conditional in C can use logical operators such as && and || to test multiple expressions and ! to negate an expression.