C Aptitude Questions and answers with explanation

C Aptitude 20
C program is one of most popular programming language which is used for core level of coding across the board. C program is used for operating systems, embedded systems, system engineering, word processors,hard ware drivers, etc.

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In the coming days, we will post C aptitude questions, answers and explanation for interview preparations.

The C aptitude questions and answers for those questions along with explanation for the interview related queries.

We hope that this questions and answers series on C program will help students and freshers who are looking for a job, and also programmers who are looking to update their aptitude on C program.
Some of the illustrated examples will be from the various companies, and IT industry experts.
Read more about C Programming Language . and read the C Programming Language (2nd Edition). by K and R.

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

C aptitude 20.1

  main()
{
int *j;
{
int i=10;
j=&i;
}
printf("%d",*j);
}


Answer: 10

Explanation: The variable i is a block level variable and the visibility is inside that block only. But the lifetime of i is lifetime of the function so it lives up to the exit of main function. Since the i is still allocated space, *j prints the value stored in i since j points i.

C aptitude 20.2

   main()
{
int i=-1;
-i;
printf("i = %d, -i = %d n",i,-i);
}


Answer: i = -1, -i = 1

Explanation: -i is executed and this execution doesn’t affect the value of i. In printf first you just print the value of i. After that the value of the expression -i = -(-1) is printed.

C aptitude 20.3

     main()
{
const int i=4;
float j;
j = ++i;
printf("%d %f", i,++j);
}

Answer: Compiler error

Explanation: i is a constant. you cannot change the value of constant

C aptitude 20.4

      main()
{
int a[2][2][2] = { {10,2,3,4}, {5,6,7,8} };
int *p,*q;
p=&a[2][2][2];
*q=***a;
printf("%d..%d",*p,*q);
}

Answer: garbagevalue..1

Explanation: p=&a[2][2][2] you declare only two 2D arrays. but you are trying to access the third 2D(which you are not declared) it will print garbage values. *q=***a starting address of a is assigned integer.

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