Chapter 1.2 - Exemplify the elementary C concept through sample programs | Part - 3
SAMPLE PROGRAM OF 3 - INTEREST CALCULATION
The program in Fig. 5 calculates the value of money at the end of each year of investment, assuming an interest rate of 11 percent and prints the year, and the corresponding amount, in two columns. The output is shown in Fig. 6 for a period of 10 years with an initial investment of 5000.00. The program uses the following formula.
Value at the end of the year = Value at the start of the year (1 + interest rate)
In the program, the variable value represents the value of money at the end of the year while the amount represents the value of money at the start of the year. The statement
amount = value;
makes the value at the end of the current years as the value start of the next year.
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| Fig. 5 Program For Investment Problem |
Let us consider the new features introduced in this program. The 5 and 6 lines begin with #define instructions. A #define instruction defines value to a symbolic constant for use in the program. Whenever a symbolic name is encountered, the compiler substitutes the value associated with the name automatically. To change the value, we have to simply change the definition. In this example, we have defined two symbolic constant PERIOD and PRINCIPAL and assigned values 10 and 5000.00 respectively. These values remain constant throughout the execution of the program.
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| Fig. 6 Output of the investment program |
The #define Directive
A #define is a preprocessor compiler directive and not a statement. Therefore #define lines should not end with a semicolon. A symbolic constant is generally written in uppercase so that they are easily distinguished from lowercase variable names. #define instructions are usually placed at the beginning before the main() function. A symbolic constant is not declared in the declaration section.
We must note that the defined constants are not variables. We may not change their values within the program by the assignment statement. For example, the statement
PRINCIPLE = 10000.00;
The declaration section declares years as integer and amount, value and inrate as floating point numbers. Note all the floating-point variables are declared in one statement. They can also be declared as
float amount; float value; float inrate;
When two or more variables are declared in one statement, they are separated by a comma.
All computations and printing are accomplished in a while loop. while is a mechanism for evaluating repeatedly a statement or a group statements. In this case, as long as the value of year is less than or equal to the value of PERIOD, the four statement that follows while being executed. Note that these four statements are grouped by braces. We exit the loop when the year becomes greater than PERIOD.
C supports the basic four arithmetic operators (*,/,+,-) along with serval other.
