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Q.42 What is the return value of f(p,p), if the value of p is initialized to 5 before the call? Note that | Q.42 What is the return value of f(p,p), if the value of p is initialized to 5 before the call? Note that | ||
the first parameter is passed by reference, whereas the second parameter is passed by value. | the first parameter is passed by reference, whereas the second parameter is passed by value. | ||
| − | + | <syntaxhighlight lang="c"> | |
int f (int &x, int c) { | int f (int &x, int c) { | ||
c = c - 1; | c = c - 1; | ||
| Line 8: | Line 8: | ||
return f(x,c) * x; | return f(x,c) * x; | ||
} | } | ||
| − | + | </syntaxhighlight > | |
(A) 3024 | (A) 3024 | ||
| Line 18: | Line 18: | ||
===Solution=== | ===Solution=== | ||
| + | In GATE 2013 marks were given to all as the same code in C/C++ produces undefined behavior. This is because * is not a sequence point. The correct code must replace | ||
| + | return f(x,c) * x; | ||
| + | with | ||
| + | res = f(x,c); | ||
| + | return res * x; | ||
| + | |||
| + | In this code, there will be 4 recursive calls with parameters (6,4), (7,3), (8,2) and (9,1). The last call returns 1. But, because of pass by reference, in all the previous functions, x is now 9. Hence, the value returned by f(p,p) will be 9 * 9 * 9 * 9 * 1 = 6561. | ||
| + | |||
| + | {{Template:FBD}} | ||
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| + | [[Category: GATE2013]] | ||
| + | [[Category: Previous year GATE questions]] | ||
| + | [[Category:Coding Questions]] | ||
Q.42 What is the return value of f(p,p), if the value of p is initialized to 5 before the call? Note that the first parameter is passed by reference, whereas the second parameter is passed by value.
<syntaxhighlight lang="c">
int f (int &x, int c) {
c = c - 1; if (c==0) return 1; x = x + 1; return f(x,c) * x;
} </syntaxhighlight > (A) 3024
(B) 6561
(C) 55440
(D) 161051
In GATE 2013 marks were given to all as the same code in C/C++ produces undefined behavior. This is because * is not a sequence point. The correct code must replace
return f(x,c) * x;
with
res = f(x,c); return res * x;
In this code, there will be 4 recursive calls with parameters (6,4), (7,3), (8,2) and (9,1). The last call returns 1. But, because of pass by reference, in all the previous functions, x is now 9. Hence, the value returned by f(p,p) will be 9 * 9 * 9 * 9 * 1 = 6561.
Q.42 What is the return value of f(p,p), if the value of p is initialized to 5 before the call? Note that the first parameter is passed by reference, whereas the second parameter is passed by value.
<syntaxhighlight lang="c">
int f (int &x, int c) {
c = c - 1; if (c==0) return 1; x = x + 1; return f(x,c) * x;
} </syntaxhighlight > (A) 3024
(B) 6561
(C) 55440
(D) 161051
In GATE 2013 marks were given to all as the same code in C/C++ produces undefined behavior. This is because * is not a sequence point. The correct code must replace
return f(x,c) * x;
with
res = f(x,c); return res * x;
In this code, there will be 4 recursive calls with parameters (6,4), (7,3), (8,2) and (9,1). The last call returns 1. But, because of pass by reference, in all the previous functions, x is now 9. Hence, the value returned by f(p,p) will be 9 * 9 * 9 * 9 * 1 = 6561.
GATECSE