Sams Teach Yourself C in 21 Days

12: while (1)

13: {

14: printf(“\nEnter the string to convert (blank to exit): “);

15: gets(buf);

16:

17: if ( strlen(buf) == 0 )

18: break;

19:

20: d = atof( buf );

21:

22: printf(“The converted value is %f.”, d);

23: }

24: return 0;

25: }

Enter the string to convert (blank to exit): 1009.12

The converted value is 1009.120000.

Enter the string to convert (blank to exit): abc

The converted value is 0.000000.

Enter the string to convert (blank to exit): 3

The converted value is 3.000000.

Enter the string to convert (blank to exit):

Thewhileloop on lines 12–23 lets you keep running the program until you enter

a blank line. Lines 14 and 15 prompt for the value. Line 17 checks whether a

blank line is entered. If it is, the program breaks out of the whileloop and ends. Line 20

callsatof(), converting the value entered (buf) to a type double,d. Line 22 prints the

final result.

Character Test Functions ....................................................................................

The header file ctype.h contains the prototypes for a number of functions that test char-

acters, returning TRUEorFALSEdepending on whether the character meets a certain con-

dition. For example, is it a letter or is it a numeral? The isxxxx()functions are actually

macros, defined in ctype.h. You learn about macros on Day 21, “Advanced Compiler

Use.” At that time, you might want to look at the definitions in ctype.h to see how they

work. For now, you only need to see how they’re used.

Theisxxxx()macros all have the same prototype.

int isxxxx(int ch);

506 Day 17

LISTING17.15 continued

INPUT/

OUTPUT

ANALYSIS

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