reverse a word

hello all,

please help me to understand the following code; it compile fine but the it gives the correct result only for a word of length =< 3. However if I comment out the statement printf("len = %d\n",len) it works fine for all inputs.

Code:

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# include <stdio.h>
# include <string.h>

char *ptr;


 
int main(int args, char *argv[]){
     
 int len = strlen(argv[1]);
 //printf("len = %d\n",len);
 int j = len - 1, i;
 char ch[len];
        for( ptr=argv[1],i=0; i<len; i++,j--){       
               
              ch[i]=*(ptr + j);
              }
                         
                printf(ch);
                printf("\n");
           
      system("PAUSE");
      }

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You probably want ch[len+1] and and then put ch[i] = '\0' after the reversing loop.

Of course, ch[len] is non-standard even for C99 compilers, so if you want to follow C standard coding, you'd have to either use a statically sized buffer [remember to check the length before copying], or call malloc to allocate a suitable size string space [don't forget the +1 for the terminating zero].

And

Code:

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printf("%s\n", ch);

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is probably a better solution, as you would get "interesting" results if the user inputs "d%" or some such [and the right combination of % in the input may even cause a crash]

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Mats