Learn to Program with C_ Learn to Program using the Popular C Programming Language ( PDFDrive )

Chapter 8 ■ Arrays
You can change 40 to any size you wish. If in has been declared as FILE *, we can prompt the
user for the file name and test if everything is okay with this:
printf("Enter name of file: ");
scanf("%s", dataFile);
if ((in = fopen(dataFile, "r")) == NULL) {
printf("File cannot be found\n");
exit(1);
}
Since we are using %s to read the name of the file, the name may not contain a space. If your
file name may contain a space, you can use gets.
8.7 Array as Argument to a Function
In Chapter 7, we saw how arguments are passed to functions. In C, arguments are passed
“by value.” When an argument is passed “by value,” a temporary location is created with the value
of the argument, and this temporary location is passed to the function. The function never has
access to the original argument.
We also saw that when, for instance, we use gets(item) to read a string into the character
array item, the function is able to put the string into the argument item. This implies that the
function has access to the actual argument – no copy is involved.
In C, an array name denotes the address of its first element. When we use an array name as an
argument to a function, the address of the first element is passed to the function that, therefore,
has access to the array.
We now take a closer look at some issues involved in writing functions with array arguments.
We will write a function, sumList, which returns the sum of the integers in an array passed to
the function. For example, if the array contains the following:
the function should return 24.
We could write the function header like this:
int sumList(int num[])
The array argument is written just like an array declaration but with no size specified.
However, the square brackets must be present to distinguish it from a simple argument. For
instance, if we had written int num, this would mean that num is an ordinary int variable.
You can specify a size, if you wish, using a constant, a symbolic constant, or any integer
expression that can be evaluated at the time the program is compiled. (C99 and later versions of
C allow variable-length arrays in which an array subscript can be specified at runtime. We will see
an example in Section 9.4.1.) However, your program will be more flexible if you do not.
211
www.it-ebooks.info