COMPUTER PROGRAMMING 1Assignment

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 becomes 12”. We could use any value instead of 12

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.

int feet, ins, metres;

orfloat feet, ins, metres;

Note we can define several variables in a single statement.

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()

{

int feet, 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

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

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.

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()

{

int feet, inches ;

printf(“Enter quantity of feet: “);

scanf(“%d“, &feet ) ;

inches = feet * 12 ;

printf(“The number of inches is %d“, inches ) ;

}

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).

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()

{

int num1, 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);

}

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.

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.