Understanding calling one function inside another C - c

Question

I'd like to ask the following misunderstandings of C language, which I see I'm having.
I'm sorry if the code is not properly indented, I tried as much as I could but there are not so many guides on the internet.
The program asked given a starting number 'val' and a Even-Odd or Odd-Even alternating sequence (which stops whenever this rules is violated) to print the greater prime number with 'val'.
I tried with two functions and the main: one to control the GCD between two given numbers and the other to keep tracks of the greatest one, but I think I miss something in the code or in the conception of C function,
Because when compiled it returns me 0 or great number which I'm not entering.
One example to understand what I should do:
If my sequence was 10, 7, 8, 23 and my val was 3, I had to print 23, because it is the greatest integer prime with 3.
Here's the code :
#include <stdio.h>
int mcd(int a, int b)
{ // Gcd function
if (a == 0)
return b;
else
return mcd(b % a, b);
}
int valuta(int val, int h) // Valuing Max function
{
int temp = 0;
if (mcd(val, h) == 1 && h > temp)
temp = h;
return temp;
}
int main()
{
int val, d, x, y, z, t, contatore = 1;
scanf("%d", &val);
scanf("%d%d", &x, &y);
if (x > y && mcd(val, x) == 1)
{ // Two options
t = x;
}
else if (y > x && mcd(val, y) == 1)
{
t = y;
}
if ((x % 2 == 0 && y % 2 == 0) || (x % 2 == 1 && y % 2 == 1))
{ // Bad case
if (x > y && mcd(val, x) == 1)
{
t = x;
contatore = 0;
}
else if (y > x && mcd(val, y) == 1)
{
t = y;
contatore = 0;
}
}
else
{
while (contatore == 1)
{
scanf("%d", &z);
t = valuta(val, z);
if (x % 2 == 0 && z % 2 == 0)
{ // Even- Odd - Even
scanf("%d", &d);
t = valuta(val, d);
if (d % 2 == 0)
{
contatore = 0;
}
else
{
contatore = 0;
}
}
if (x % 2 == 1 && z % 2 == 1)
{ //Odd- Even- Odd
scanf("%d", &d);
t = valuta(val, d);
if (d % 2 == 1)
{
contatore = 0;
}
else
{
contatore = 0;
}
}
}
}
printf("%d\n", t);
return 0;
}
PS. Is there any way to reduce the number of lines of code or to reduce the effort in coding? I mean, a straightforward solution will be helpful.

Answer 1

Your valuta() function is flawed in that it needs to return the maximum qualifying value so far but has no knowledge of the previous maximum - temp is always zero. The following takes the previous maximum as an argument:
int valuta(int val, int h, int previous )
{
return ( mcd(val, h) == 1 && h > previous ) ? h : previous ;
}
And is called from main() thus:
t = valuta( val, x, t ) ;
The test mcd(val, h) == 1 is flawed, because mcd() only ever returns the value of parameter b which is not modified in the recursion, so will never return 1, unless the argument b is 1. Since I have no real idea what mcd() is intended to do, I cannot tell you how to fix it. It appear to be a broken implementation of Euclid's greatest common divisor algorithm, which correctly implemented would be:
int mcd(int a, int b)
{
if(b == 0)
return a;
else
return mcd(b, a % b);
}
But I cannot see how that relates to:
"[...] he greatest integer prime with 3 [...]
The odd/even even/odd sequence handling can be drastically simplified to the extent that it is shorter and simpler than your method (as requested) - and so that it works!
The following is a clearer starting point, but may not be a solution since it is unclear what it is it is supposed to do.
#include <stdio.h>
#include <stdbool.h>
int mcd(int a, int b)
{
if(b == 0)
return a;
else
return mcd(b, a % b);
}
int valuta(int val, int h, int previous )
{
return ( mcd(val, h) && h > previous ) ? h : previous ;
}
int main()
{
int val, x, t ;
printf( "Enter value:") ;
scanf("%d", &val);
typedef enum
{
EVEN = 0,
ODD = 1,
UNDEFINED
} eOddEven ;
eOddEven expect = UNDEFINED ;
bool sequence_valid = true ;
printf( "Enter sequence in odd/even or even/odd order (break sequence to exit):\n") ;
while( sequence_valid )
{
scanf("%d", &x);
if( expect == UNDEFINED )
{
// Sequence order determined by first value
expect = (x & 1) == 0 ? EVEN : ODD ;
}
else
{
// Switch expected odd/even
expect = (expect == ODD) ? EVEN : ODD ;
// Is new value in the expected sequence?
sequence_valid = (expect == ((x & 1) == 0 ? EVEN : ODD)) ;
}
// If the sequence is valid...
if( sequence_valid )
{
// Test if input is largest qualifying value
t = valuta( val, x, t ) ;
}
}
// Result
printf("Result: %d\n", t);
return 0;
}