Logical and Relational Operators

We can use these operators to define the conditions under which conditional and iterative constructs are executed. Logical operators are not(!), and(&&) and or(||) and relational operators are greater than(>), less than(<), greater than or equal to(>=), less than or equal to(<=), equal to(==) and not equal to(!=).

Logical AND example

Martha wants a program to check if her students are between a certain height - students who are too short or too tall cannot be placed on the carnival ride. She comes up with the following code:

#include <stdio.h>

int main() {
  float height;
  printf("Please enter your height: ");
  scanf("%f", &height);

  if (height < 180 && height > 120) {
    printf("You can enter the ride!\n");
  } else {
    printf("Please do not enter the ride\n");
  }

  return 0;
}

The condition height<180 && height>120 only evaluates to true when both of the comparisons evaluate to true, that is, when the height of the student is both greater than 120(height>120) and less than 180(height<180).

Logical OR example

Consider a scenario where we want to check which of a list of numbers is a multiple of 2 OR 3:

#include <stdio.h>

int main(void) {
  for (int number = 0; number <= 20; number++) {
    if (!(number % 2 == 0 || number % 3 == 0)) {
      printf("\033[0;41m %d - NOT DIVISIBLE by 2 or 3\n", number);
    } else {
      printf("\033[0;32m %d - DIVISIBLE by 2 or 3\n", number);
    }
  }

  return 0;
}

Recall that %(the modulo operator) is used to get the remainder of a division and a number is divisible by another if the remainder is 0.

Coloring text using color codes in the terminal

Read more about coloring the text in the terminal from this C for dummies article.