Computer Programming 1

1. Computer Programming 1 Assignment

2. Assignment • We have used gets to input a value into variable • The second way to give a variable a value is known as assignment • Assignment allows us to give a value to the variable directly in a program • We may give the variable a constant value or use the value of other variables. • For example, suppose we have a variable called feet which we wish to give the value 12. In C we write: feet = 12; • This can be read as “feet is assigned the value 12” or “feet becomes12”. • We could use any value instead of 12

3. Assignment • Other examples of assigning values to variables might be: feet = 130; ins = 10; metres = 4; • We must have declared the variable above before we can use them e.g. intfeet, ins, metres; or float feet, ins, metres; • Note we can define several variables in a single statement.

4. Assignment: Example • Consider a program to convert feet to inches. A simple (and fairly useless) C program to do this might be: /* convert.c: converts feet to inches Author: Joe Carthy Date: 01/01/94 */ main() { intfeet, inches; feet = 10; inches = feet * 12 ; printf(“The number of inches is %d \n“, inches ) ; } • Executing this program produces as output: The number of inches is 120

5. Assignment: Example • Pictorially, after execution of the second assignment statement, the variables in memory may be visualised as. • Here we use the value of one variable (feet) to compute the value of another variable (inches). Memory 120 inches 10 feet

6. Assignment • Other examples of such an assignment are: pints = gallons * 8; cms= (km * 100000) + (m * 1000); where the values of variables on the right hand side are used to compute the values assigned to the variables on the left hand side of the assignment.

7. Assignment: User Input • The program to convert feet to inches as presented above is very limited in that it always produces the same answer. • It always converts 12 feet to inches. • A better version would ask the user to enter the number of feet to be converted and display the appropriate result: /* convert2.c: convert feet to inches, Version 2 Author: Joe Carthy Date: 01/01/94 */ main() { intfeet, inches ; printf(“Enter quantity of feet: “); scanf(“%d“, &feet ) ; inches = feet * 12 ; printf(“The number of inches is %d“, inches ) ; }

8. Assignment: User Input • Executing this program produces as output: Enter quantity of feet: 4 The number of inches is 48 • The scanf(“%d“, &feet) statement reads a whole number from the keyboard and stores it in the variable feet. • The & character is vital and scanf() will not function properly without it. • Yes it has a messy look to it, but unfortunately in the C programming language this is one of the common methods for reading such quantities. • The %d tells scanf() to read a whole number; %f can be used to read a real number; %c to read a character and %s to read a string (containing no spaces e.g. a single word).

9. Assignment: Example 2 • As another example of the use of I/O and variables consider a simple calculator program which prompts for two numbers, adds them and displays the sum: /* calc.c: calculator program Author: Joe Carthy Date: 01/01/94 */ main() { intnum1, num2, sum; printf(“Enter first number: “); scanf(“%d”, &num1 ); printf(“Enter second number: “); scanf(“%d“, &num2 ); sum = num1 + num2 ; printf(“The sum of %d and %d is %d “, num1, num2, sum); }

10. Assignment: Example 2 • Executing this program produces as output: Enter first number: 14 Enter second number: 10 The sum of 14 and 10 is 24 • NOTE: in this program, we illustrate that a single printf() can display the value of a number of variables, in this case the values of three variables are displayed.

11. Assignment: Portfolio Exercises • The following programs should prompt the user to enter the required data and display an appropriate message that explains the output. • You should use the float type where appropriate. It is used for real numbers – numbers with a decimal point. • Write a program (WAP) to read the base and height of a triangle and display the area • WAP to read the radius of a circle and display the area – take PI as 3.1417 • WAP to read in an amount of Euros and convert it to Sterling – assume 1E = 0.85Stg • For each program, draw memory maps showing the variables and the values they have at the end of executing the program.