C Interview Questions & Answers

[Kalyan]

C Interview Questions & Answers

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

1. void main(){
int const * p=5;
C Aptitude
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+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[ s ] may be surprising. But in the case of C it is same as
s.

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 precision 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 (== , >, <, <=, >=,!= ) .

4. main() {
static int var = 5;
printf("%d ",var--);
if(var)
main();
}

Answer:
5 4 3 2 1

Explanation:
When static storage class is given, it is initialized once. The change in the value of a static variable is retained even between the function calls. Main is also treated like any other ordinary function, which can be called recursively.

5. main(){
int c[ ]={2.8,3.4,4,6.7,5};
int j,*p=c,*q=c;
for(j=0;j<5;j++) {
printf(" %d ",*c);
++q; }
for(j=0;j<5;j++){
printf(" %d ",*p);
++p; }
}

Answer:
2 2 2 2 2 2 3 4 6 5

Explanation:
Initially pointer c is assigned to both p and q. In the first loop, since only q is incremented and not c , the value 2 will be printed 5 times. In second loop p itself is incremented. So the values 2 3 4 6 5 will be printed.