chapter09

# chapter09 - COP 3275 Chapter 09 Jonathan C.L Liu Ph.D CISE...

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COP 3275: Chapter 09 Jonathan C.L. Liu, Ph.D. CISE Department University of Florida, USA

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Introduction A function is a series of statements that have been grouped together and given a name. Each function is essentially a small program, with its own declarations and statements. Advantages of functions: A program can be divided into small pieces that are easier to understand and modify. We can avoid duplicating code that’s used more than once. A function that was originally part of one program can be reused in other programs. 2
Defining and Calling Functions Before we go over the formal rules for defining a function, let’s look at three simple programs that define functions. 3

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Program: Computing Averages A function named average that computes the average of two double values: double average(double a, double b) { return (a + b) / 2; } The word double at the beginning is the return type of average . The identifiers a and b (the function’s parameters ) represent the numbers that will be supplied when average is called. 4
Program: Computing Averages Every function has an executable part, called the body, which is enclosed in braces. The body of average consists of a single return statement. Executing this statement causes the function to “return” to the place from which it was called; the value of (a + b) / 2 will be the value returned by the function. 5

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Program: Computing Averages A function call consists of a function name followed by a list of arguments. average(x, y) is a call of the average function. Arguments are used to supply information to a function. The call average(x, y) causes the values of x and y to be copied into the parameters a and b . An argument doesn’t have to be a variable; any expression of a compatible type will do. average(5.1, 8.9) and average(x/2, y/3) 6
Program: Computing Averages We’ll put the call of average in the place where we need to use the return value. A statement that prints the average of x and y : printf("Average: %g\n", average(x, y)); The return value of average isn’t saved; the program prints it and then discards it. If we had needed the return value later in the program, we could have captured it in a variable: avg = average(x, y); 7

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Program: Computing Averages The average.c program reads three numbers and uses the average function to compute their averages, one pair at a time: Enter three numbers: 3.5 9.6 10.2 Average of 3.5 and 9.6: 6.55 Average of 9.6 and 10.2: 9.9 Average of 3.5 and 10.2: 6.85 8
average.c /* Computes pairwise averages of three numbers */ #include <stdio.h> double average(double a, double b) { return (a + b) / 2; } int main(void) { double x, y, z; printf("Enter three numbers: "); scanf("%lf%lf%lf", &x, &y, &z); printf("Average of %g and %g: %g\n", x, y, average(x, y)); printf("Average of %g and %g: %g\n", y, z, average(y, z)); printf("Average of %g and %g: %g\n", x, z, average(x, z)); return 0; } 9

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Program: Printing a Countdown To indicate that a function has no return value, we specify that its return type is
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chapter09 - COP 3275 Chapter 09 Jonathan C.L Liu Ph.D CISE...

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