java - Recursive function with local variable not executing if statement - 


public int count7(int n)  {     int count = 0;     if (n%10 == 7) count= 1;     if(n%10 != 7) count= 0;      if (n < 10 && n==7) return 1;     if (n < 10 && n!=7) return 0;     else return count7(n/10) + count; }

i have above function recursively adds occurrences of 7 in given number. each time divides number 10 reduce 1 number , checks if last digit equals 7.

when run count7(7), returns 1. have question regarding why never hits first if statement (if n%10 == 7) count = 1;

if program written as: 

public int count7(int n)  {     int count = 0;     if (n%10 == 7) count= 0;     if(n%10 != 7) count= 0;      if (n < 10 && n==7) return 1;     if (n < 10 && n!=7) return 0;     else return count7(n/10) + count; }

the call count7(7) still work. question recursive calls placed on stack, why last call not assign count 1 , instead assign 0?

eg:

count7(717)

count7(7) + count <-------this hits base case since n < 10 count(71) + count count(717) + count

count assigned 1 whenever n % 10 == 7. base case returns 1. please explain 1 case thing not able understand properly.

you have 3 return statements in play

if (n < 10 && n==7) return 1; if (n < 10 && n!=7) return 0; else return count7(n/10) + count;

only third 1 (the recursive case) uses count variable @ all. when count7(7), triggers base case immediately, returning 1 without ever caring count equal to, because first return statement used instead of third, imagine you're expecting.


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