c语言 int与float 计算,c语言初学，int和float的区别

#21

hjx11202016-03-21 22:35

这是《C primer plus》的教材，很详细

Listing 2.1. The first.c Program

#include

int main(void) /* a simple program */

{

int num; /* define a variable called num */

num = 1; /* assign a value to num */

printf("I am a simple "); /* use the printf() function */

printf("computer.n");

printf("My favorite number is %d because it is first.n",num);

return 0;

}

If you think this program will print something on your screen, you're right! Exactly what will be

printed might not be apparent, so run the program and see the results. First, use your favorite

editor (or your compiler's favorite editor) to create a file containing the text from Listing 2.1.

Give the file a name that ends in .c and that satisfies your local system's name requirements.

You can use first.c, for example. Now compile and run the program. (Check Chapter 1,

"Getting Ready," for some general guidelines to this process.) If all went well, the output should

look like the following:

I am a simple computer.

My favorite number is 1 because it is first.

All in all, this result is not too surprising, but what happenedto the ns and the %d in the

program? And some of the lines in the program do look strange. It's time for an explanation

The Example Explained

We'll take two passes through the program's source code. The first pass ("Pass 1: Quick

Synopsis") highlights the meaning of each line to help you get a general feel for what's going on.

The second pass ("Pass 2: Program Details") explores specific implications and details to help

you gain a deeper understanding.

Figure 2.1 summarizes the parts of a C program; it includes more elements than our first

example uses.

Figure 2.1. Anatomy of a C program.

Pass 1: Quick Synopsis

This section presents each line from the program followed by a short description; the next

section (Pass 2) explores the topics raised here more fully.

#include include another file

This line tells the compiler to include the information found in the file stdio.h, which is a

standard part of all C compiler packages; this file provides support for keyboard input and for

displaying output.

int main(void) a function name

C programs consist of one or more functions, the basic modules of a C program. This program

consists of one function called main. The parentheses identify main() as a function name. The

int indicates that the main() function returns an integer, and the void indicates that main()

doesn't take any arguments. These are matters we'll go into later. Right now, just accept both

int and void as part of the standard ISO/ANSI C way for defining main(). (If you have a pre-

ISO/ANSI C compiler, omit void; you may want to get something more recent to avoid

incompatibilities.)

/* a simple program */ a comment

The symbols /* and */ enclose comments, remarks that help clarify a program. They are

intended for the reader only and are ignored by the compiler.

{ beginning of the body of the function

This opening brace marks the start of the statements that make up the function. The function

definition is ended with a closing brace (}).

int num; a declaration statement

This statement announces that you are using a variable called num and that num will be an int

(integer) type.

num = 1; an assignment statement

The statement num = 1; assigns the value 1 to the variable called num.

printf("I am a simple "); a function call statement

The first statement using printf() displays the phrase I am a simple on your screen, leaving

the cursor on the same line. Here printf() is part of the standard C library. It's termed a

function, and using a function in the program is termed calling a function.

printf("computer.n"); another function call statement

The next call to the printf() function tacks on computer to the end of the last phrase printed.

The n is code telling the computer to start a new line—that is, to move the cursor to the

beginning of the next line.

printf("My favorite number is %d because it is first.n", num);

The last use of printf() prints the value of num (which is 1) embedded in the phrase in quotes.

The %d instructs the computer where and in what form to print the value of num.

return 0; a return statement

A C function can furnish, or return, a number to the agency that used it. For the present, just

regard this line as part of the ISO/ANSI C requirement for a properly written main() function.

} the end

As promised, the program ends with a closing brace.

Now that you have an overview of Listing 2.1, we'll take a closer look. Once again, we'll examine

the individual lines from the program, this time using each line of code as a starting point for

going deeper into the details behind the code and as a basis for developing a more general

perspective of C programming features.