CODEWITHSUNDEEP
cperformanceoptimizationwhile-loopinfinite-loop
Tapasweni Pathak
Tapasweni Pathak

Reputation: 562

what is wrong with the loops

I am solving a problem of adding the last digits of numbers lying between a range (for ex. between 'm' and 'n' where m < n).I have coded this

 #include <stdio.h>

 int main()
 {
 int t=0;
 long int m=0,n=0,num=0,sum=0,lsum=0,i=0;
 scanf("%d",&t);
 while(t--){
    scanf("%ld%ld",&m,&n);
    i=m;
    while(i<=n){
       while(i!=0){
          num=i%10;
          i/=10;
       }
       lsum=lsum+(sum%10);
       i++;
    }
}
printf("\n%ld",lsum);
return 0;
}

Here t=No of Test Cases. m and n is the range. I don't know why it is running infinitely in the terminal. I am using gcc(4.3.2) compiler.How can I optimize it for speed ,or is it the case where the while conditions are never terminated, but why?

Upvotes: 3

Views: 166

Answers (2)

Hicham
Hicham

Reputation: 979

There is an infinite loop int the code : 

 while(i<=n)
 {       
     while(i!=0)
   {        
      num=i%10;        
      i/=10; 
   }       
   lsum=lsum+(sum%10);       
   i++;    
 }

the first while(1<= n) is always true : the second loop makes i = 0 or i = 1 !

Upvotes: 4

Petar Minchev
Petar Minchev

Reputation: 47363

You are dividing the i: i/=10. This means that i is always set back to 1 at the end of the loop. You should use a temporary variable for the dividing. Like this:

    while(i<=n){
       int temp = i;
       while(temp !=0){
          num=temp %10;
          temp /=10;
       }
       lsum=lsum+(sum%10);
       i++;
    }

P.S. There are many other errors in your code. But they are not connected with the infinite looping.

Upvotes: 4

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