c - Explanation of a program using functions

Question

#include <stdio.h>

float a(int n);

main()
{
    int N;
    float z;
    puts("Dose to n (>=2)");
    scanf("%d",&N);
    z=a(N);
    printf("Gia n=%d h anadromikh sxesh dinei %f
",N,z);
}


float a(int n)
{  
    if(n==2)
        return (7);
    else if(n==3) 
        return ((8*49-1)/1);
    else 
        return ((8*a(n-1)*a(n-1)-1)/a(n-2));


}

guys can you please explain me how this program works? i mean, if i put for example n=8 , how will it find a7,a6 etc so it get the a8 ??

Answer 1

Basically,

In CC++ Programming the function call work on Stack Segment in Memory.See Here

and in your program you are calling function recursively.

return ((8*a(n-1)*a(n-1)-1)/a(n-2)); at this stage for input n = 8

The function all will be

for a(8)->(8*a(7)*a(7)-1)/a(6)))

for a(7)->(8*a(6)*a(6)-1)/a(5)))

for a(6)->(8*a(5)*a(5)-1)/a(4)))

for a(5)->(8*a(4)*a(4)-1)/a(3)))

for a(4)->(8*a(3)*a(3)-1)/a(2)))

for a(3) program will return (8*49-1)/1

for a(2) program will return (7)

These all function will get its own stack segment in stack memory.

And the stack segment as it works on LIFO.

the stack segment will be from Last a(8)->a(7)->a(6)->a(5)->a(4)->a(3)->a(2) and it depends on the compiler`s function calling methodology so stack segment function calling may vary. hope this will help you to understand.