Need to understand the working of the while loop condition in the below C program

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C++

/* The below program receives strings from keyboard and writes them to file */
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
void main( )
{
FILE *p ;
char string[80] ;
p = fopen ( "check.txt", "w" ) ;
if ( p == NULL )
{
puts ( "Unable to open file" ) ;
exit(1) ;
}
printf ( "\nEnter text :\n" ) ;
while ( strlen ( gets ( string ) ) > 0 )
{
fputs ( string, p ) ;
fputs ( "\n", p ) ;
}
fclose ( p ) ;
getch();
}

In the above program I am not able to understand the working of the while condition >> while ( strlen ( gets ( string ) ) > 0 ) <<

Please help me understand it.Please let me know if more clarity in the question is needed.

Posted 4-Dec-14 13:46pm

Member 11287281

Updated 4-Dec-14 16:18pm

Chris Maunder774.2K

v4

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barneyman 4-Dec-14 21:17pm

like all bracketed statements, work from the inside out

gets takes string as a param, and happens to return the same string

strlen is then returning the length of that returned string

and while that returned length is >0 the loop continues

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ZurdoDev · Answer 1 · 2014-12-04T15:17:00

Solution 1

Just google the gets() function in c. Here is a link, http://www.tutorialspoint.com/c_standard_library/c_function_gets.htm[^]

In fact, the comment at the top of the code and the printf statement right before the while loop explain exactly what is happening.

Posted 4-Dec-14 15:17pm

ZurdoDev

AndersonChau · Answer 2 · 2014-12-04T15:38:00

The while loop can be read as the following :

C#

int mLen = 0;
char* strInput = gets ( string ); // console blocks here waiting for input
mLen = strlen(strInput);

while ( mLen > 0 )
{
   fputs ( string, p ) ;
   fputs ( "\n", p ) ;
   strInput = gets ( string ); // console blocks here waiting for input
   mLen = strlen(strInput);
}