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Sample Technical Questions

C Sample Question

Note : All the C sample programs are tested under Turbo C/C++ compilers.
It is assumed that,

• Programs run under DOS environment,
• The underlying machine is an x86 system,
• Program is compiled using Turbo C/C++ compiler.

The program output may depend on the information based on this assumptions (for example sizeof(int) == 2 may be assumed).

Following are some C sample questions.

Predict the output or error(s) for the following:

1. void main()
   {
   	int  const * p=5;
   	printf("%d",++(*p));
   }

   Answer:
   

   Compiler error: Cannot modify a constant value.

   Explanation:

   p is a pointer to a "constant integer". But we tried to change the value of the "constant integer".

2. main()
   {
   	char s[ ]="man";
   	int i;
   	for(i=0;s[ i ];i++)
   	printf("\n%c%c%c%c",s[ i ],*(s+i),*(i+s),i[s]);
   }

   Answer:

   mmmm
   aaaa
   nnnn

   Explanation:

   s[i], *(i+s), *(s+i), i[s] are all different ways of expressing the same idea. Generally array name is the base address for that array. Here s is the base address. i is the index number/displacement from the base address. So, indirecting it with * is same as s[i]. i[s] may be surprising. But in the case of C it is same as s[i].

3. main()
   {
   	float me = 1.1;
   	double you = 1.1;
   	if(me==you)
   printf("I love U");
   else
   		printf("I hate U");
   }

   Answer:

   I hate U

   Explanation:

   For floating point numbers (float, double, long double) the values cannot be predicted exactly. Depending on the number of bytes, the precession with of the value represented varies. Float takes 4 bytes and long double takes 10 bytes. So float stores 0.9 with less precision than long double.

   Rule of Thumb:

   Never compare or at-least be cautious when using floating point numbers with relational operators (== , >, <, <=, >=,!= ).

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