scanf in C

8 Key excerpts on "scanf in C"

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  eBook - PDF

  Computer Simulation in Physics and Engineering

  • Martin Oliver Steinhauser(Author)
  • 2012(Publication Date)
  • De Gruyter

    (Publisher)

  In a way, this function is the complement of printf() , see Section 2.2.6 on Page 117. The data stream is read from (stdin), which usually is the keyboard. scanf() – like printf() – is declared in the header file , which is why you have to include this header file, as in Listing 14. When you run this program, you are asked in line 7 to enter an integer. 25 In pure C++ these functions could easily be generalized to return whatever types of real , complex , or integer variables through the use of classes and templates. Section 2.2 First steps in C 123 Listing 13. Use of predefined macros. (*) 1 #include 2 #include 3 4 #if defined ( __STDC_VERSION__ )&& __STDC__VERSION >= 199901 L 5 void function( void ) { 6 printf ( Name of t h i s f u n c t i o n : %s n , __func__) 7 } 8 #else 9 void function( void ) { 10 printf ( No C99 s t a n d a r d c o m p i l e r n ); 11 } 12 #endif 13 14 int main ( void ) { 15 #ifdef __STDC__ 16 printf ( Using an ANSI C c o m p i l e r n ); 17 #endif 18 printf ( Date of c o m p i l a t i o n : %s n , __DATE__); 19 printf ( Time of c o m p i l a t i o n : %s n , __TIME__); 20 21 printf ( Line : %3d | F i l e : %s n , __LINE__ , __FILE__ ); 22 #line 99 f i l e . c /* sets the line number and the file name */ 23 printf ( Line : %3d | F i l e : %s n , __LINE__ , __FILE__ ); 24 function (); 25 return EXIT_SUCCESS ; 26 } Listing 14. Example for the use of the C scanf() function. 1 /* Usage of scanf () */ 2 #include 3 4 int main ( int argc , char *argv []) 5 { 6 int var; 7 printf ( P l e a s e e n t e r an i n t e g e r : ); 8 scanf ( %d , &var); 9 printf ( You e n t e r e d %d n , var); 10 return (0); 11 } scanf() in line 8 awaits your input, which you have to verify by pressing the return key. Then the input value is assigned to the integer variable var in line 8 and printed in line 9. The screen output when running Listing 14 is: Please enter an integer: 34567 You entered 34567

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  eBook - ePub

  Learn C Programming

  A beginner's guide to learning C programming the easy and disciplined way

  • Jeff Szuhay(Author)
  • 2020(Publication Date)
  • Packt Publishing

    (Publisher)

  to limit possible input characters section.
• printf() allows the field width and precision to be specified with the * and arguments; scanf() uses * for a completely different purpose—to suppress assignment. For instance, using * allows us to skip over an input value, if needed.
One final difference between printf() and scanf() is that in the input strings to scanf(), whitespace is critical in the process of parsing the input strings into values. We will explore this behavior next.

Reading numerical input with scanf()

To begin our exploration of scanf(), we begin by reading an integer and a double from the console. Rather than attempt to explain how scanf() interprets the input, I believe it would be far better to first get an intuitive experience of how it works. We begin with the following program:
#include <stdio.h>int main( void ) {int anInteger = -1;doubleaDouble = -1.0;printf( "Enter an integer and a decimal number: " );scanf( "%d%lf" , &anInteger , &aDouble ); printf( "1. integer:%d\n" , anInteger );printf( "2.double:%lf\n" , aDouble ); }
This simple program first initializes values that will be used to store input. If scanf() can't assign values, we will see these default values. We will use two simple numbers for now. However, as we will see, if the user enters these numbers, we will be unable to tell whether they are default values that were not assigned by scanf() or whether the user actually entered these numbers.
The program then prints a prompt for the user to enter an integer and a decimal number. It then reads what is entered using scanf()and tries to assign values to the two variables. The last two statements print the values of the two variables. The essential work of this program takes place in the single scanf() statement. Notice that even though there is no space between %d and %lf, whitespace remains an important consideration for input.