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Output of C Programs | Set 11
• Difficulty Level : Medium
• Last Updated : 27 Dec, 2016

Asked by Shobhit

 `#include``int` `fun(``int` `n, ``int` `*fg)``{``   ``int` `t, f;``   ``if``(n <= 1)``   ``{``     ``*fg = 1;``      ``return` `1;``   ``}``   ``t = fun(n-1, fg);``   ``f = t + *fg;``   ``*fg = t;``   ``return` `f;``}``int` `main( )``{``  ``int` `x = 15;``  ``printf` `( ``"%d\n"``, fun (5, &x));``  ``getchar``();``  ``return` `0;``}`

In the above program, there will be recursive calls till n is not smaller than or equal to 1.

```fun(5, &x)
\
\
fun(4, fg)
\
\
fun(3, fg)
\
\
fun(2, fg)
\
\
fun(1, fg)
```

fun(1, fg) does not further call fun() because n is 1 now, and it goes inside the if part. It changes value at address fg to 1, and returns 1.

Inside fun(2, fg)

```   t = fun(n-1, fg); --> t = 1
/* After fun(1, fg) is called, fun(2, fg) does following */
f = t + *fg;      -->  f = 1 + 1 (changed by fun(1, fg)) = 2
*fg = t;           --> *fg = 1
return f (or return 2)
```

Inside fun(3, fg)

```   t = fun(2, fg); --> t = 2
/* After fun(2, fg) is called, fun(3, fg) does following */
f = t + *fg;       -->  f = 2 + 1 = 3
*fg = t;            --> *fg = 2
return f (or return 3)
```

Inside fun(4, fg)

```   t = fun(3, fg);   --> t = 3
/* After fun(3, fg) is called, fun(4, fg) does following */
f = t + *fg;       -->  f = 3 + 2 = 5
*fg = t;            --> *fg = 3
return f (or return 5)
```

Inside fun(5, fg)

```   t = fun(4, fg);   -->  t = 5
/* After fun(4, fg) is called, fun(5, fg) does following */
f = t + *fg;       -->  f = 5 + 3 = 8
*fg = t;            --> *fg = 5
return f (or return 8 )
```

Finally, value returned by fun(5, &x) is printed, so 8 is printed on the screen

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