GATE CSE 2005 | Question: 32

Question

Consider the following C program:

double foo (double);		/* Line 1 */
int main() {
    double da, db;
    //input da
    db = foo(da);
}
double foo (double a) {
    return a;
}

The above code compiled without any error or warning. If Line $1$ is deleted, the above code will show:

• A. no compile warning or error

• B. some compiler-warnings not leading to unintended results

• C. some compiler-warnings due to type-mismatch eventually leading to unintended results

• D. compiler errors

Comments

Abhrajyoti00

I think you are talking about the fun declaration right?

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Yes Pranavpurkar.

@prateek_hazard Here after deleting Line 1 when main executes foo () it assumes it to be an int. But actually, in the function signature it is double. Hence type mismatch will occur.

But it will not lead to unintended results. Hence ans is Option D

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@Abhrajyoti00 

But it will not lead to unintended results. 

will u pls explain this ?

Answer 1

D since foo is defined after main so it should be declared before main.

Comments

Absolutely No.

Nowadays, there is no significance of writing functions before or after the main function.

You can write it anywhere.

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so what should be the answer??

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@sushmita

Answer is correct , its D only but the logic behind the solution is wrong as given by @_xor_ .

Plz read the next line what I have written .

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Let me give more insight :--

In c programming the function definition can be done anywhere , after the main or before the main . I think there is no problem.(Plz check the code in gcc compilers)

CODE 1

 double foo (double);        /* Line 1 */
int main() {

    double da, db;
    //input da

    db = foo(da);

}

double foo (double a) {
    return a;
}

CODE 2

double foo (double);        /* Line 1 */
double foo (double a) {
    return a;
}

int main() {

    double da, db;
    //input da

    db = foo(da);

}

You can see the difference as in CODE 1 I have written the function definition just above the main and in CODE 2 I have written function definition just after the main function . There is no problem with these codes.

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Coming to function prototype ------

Positioning of function prototype -

1. If function definition is written after main then and then only we write prototype declaration in global declaration section
2. If function definition is written above the main function then ,no need to write prototype declaration

Hope u understand . Let me know If I am wrong . @Arjun Sir

http://www.c4learn.com/c-programming/c-function-prototype-declaration/

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THAT I KNOW. You are right. I was confused about the point that if we write the function definition after calling the function, without even declaring the function or its prototype will it give compiler error or not???

Because i think C compiler will assume the datatypes of parameters from the call itself but the return type need to be specified.

Reference- http://stackoverflow.com/questions/2575153/must-declare-function-prototype-in-c#comment45797395_24135237

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Plz note :   I am doing all the coding in codeblock compiler that is a gcc compiler , could be run in windows environment And I have the latest version .

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double foo (double a) {
    return a;
}
int main() {
    double da, db;
    db = foo(da);
}

I have not written the prototype of this function however this code is 100 % correct . No compilation error.

So there are two rules -

1. If ur function is after the main function then u need to define the prototype unless its return type is default return type that is int.
2. If ur function is above the main function then there is no need to define the prototype.

Hope  it helps.

Answer 2

In c  if a function is called before its declaration, the compiler assumes return type of the function as int so deleting line 1 cause error.

Answer 3

When the function prototype is removed Compiler would give Type mismatch error, as already answered above.

So Answer is D

Answer 4

  

Only warning with output

 

 

 

Compiler Error 

 

References: