Lecture 6:  Conditionals

Content Tested: Conditional expressions, writing programs with conditionals

Lecture Content:

• Conditional execution
• If statement
• Conditional expressions
• Relational and logical operators
• Compound statements

Goals:

• Understand conditional expressions
• Using conditional statements in programs

Assessment Technique:  Conditionals Exercises

Purpose:

Activity:

1.  Write a C program that prompts the user to enter a number (of integer type) and prints the absolute value of this number.  For the purpose of this activity, please do not use the abs function in the math library.
(Hint:  You might want to describe the algorithm in English before writing any code.  When you have written the code, be sure to hand-trace the code with sample input values.)
 
 
 
 
 
 

2.  (Exercise 5 in chapter 4 of Hanly, Koffman)  Write a program that takes the x-y coordinates of a point in the Cartesian plane and prints a message telling either an axis on which the point lies or the quadrant in which it is found.

Sample lines of output:

(-1.0, -2.5) is in quadrant III
(0.0, 4.8) is on the y axis
 
 
 

Solutions

/* absolute value function */
/* prompts the user to enter an integer value and prints the
 * absolute value of the entered integer
 */

#include <stdio.h>

int main (void) {
   /* declarations */
   int abs_value;

   /* prompt user */
   printf("Please enter an integer.\n");
   scanf("%d", &abs_value);

   /* check to see if abs_value is < 0 */
   if(abs_value < 0){
       abs_value = -abs_value;
   }

   /* print the absolute value */
   printf("Absolute value: %d\n", abs_value);

   /* successful return */
   return 0;
}

2.

/* Program prints out the axis (or axes) on which a point lies or the
   quadrant in which a point lies.  The user is asked to enter the x
   and y coordinates of the point */

#include <stdio.h>

int main (void) {

    /* declarations */
    double x_coordinate, y_coordinate;

    /* Prompt user to enter x-coordinate value */
    printf("Please enter the x-coordinate: ");
    scanf("%lf", &x_coordinate);

    /* Prompt user to enter y-coordinate value */
    printf("Please enter the y-coordinate: ");
    scanf("%lf", &y_coordinate);

    /* check for point on x-axis */
    if(y_coordinate == 0.0){
        printf("(%f, %f) is on the x axis\n", x_coordinate, y_coordinate);
    }

    /* check for point on y-axis */
    if(x_coordinate == 0.0){
        printf("(%f, %f) is on the y axis\n", x_coordinate, y_coordinate);
    }

    /* check for quadrant I */
    else if(x_coordinate > 0.0 && y_coordinate > 0.0){
        printf("(%f, %f) is in quadrant I\n", x_coordinate, y_coordinate);
    }

    /* check for quadrant II */
    else if(x_coordinate < 0.0 && y_coordinate > 0.0){
        printf("(%f, %f) is in quadrant II\n", x_coordinate, y_coordinate);
    }

    /* check for quadrant III */
    else if(x_coordinate < 0.0 && y_coordinate < 0.0){
        printf("(%f, %f) is in quadrant III\n", x_coordinate, y_coordinate);
    }

    /* check for quadrant IV */
    else{
        printf("(%f, %f) is in quadrand IV\n", x_coordinate, y_coordinate);
    }

    /* all possibilities covered by now */

    /* terminate successfully */
    return 0;
}

Possible Uses of Activity:

• Have students work in groups to complete this activity.  The instructor may want to circulate throughout the groups to ensure that each group is making progress.  After the groups have completed the problems, the instructor can ask for volunteers for each problem.
• Have students work individually on their problems and form a small group to discuss their answers.