Computer Knowledge - MCQ Practice Questions

calloc(n, size) allocates n blocks of size bytes and initializes to 0. malloc(size) allocates size bytes without initialization. calloc() is typically slower due to initialization.

/* */ is used for multi-line comments in C. // is used for single-line comments and was introduced in C99.

Since both 5 and 2 are integers, integer division occurs ($\frac{5}{2}$ = 2). The result 2 is then converted to float as 2.000000.

In structures, each member has its own memory location. In unions, all members share the same memory location, so only one can hold a value at a time.

When static is used with a global variable, it restricts its scope to the file where it is declared. Without static, global variables are accessible across files using extern.

Array name decays to pointer. p[5] is equivalent to *(p+5) which is *(arr+5) or arr[5]. This demonstrates pointer arithmetic.

Declaration tells the compiler about a variable's name and type (e.g., 'extern int x;'). Definition actually allocates memory (e.g., 'int x = 5;'). A variable can be declared multiple times but defined only once.

++a increments a to 6 and returns 6. Then a++ returns 6 and increments a to 7. So b = 6 + 6 = 12.

An empty structure in C has a size of 1 byte. This is to ensure each structure instance has a unique address in memory.

strlen() counts characters excluding the null terminator. "Hello" has 5 characters, so strlen(s) returns 5.

The left shift operator (<<) shifts bits to the left by 1 position, which is equivalent to multiplying by 2. So 5 << 1 = 10.

p points to arr, so p[5] is equivalent to *(p+5) which gives the value at arr[5].

The void pointer is a generic pointer that can hold addresses of any data type. void is also used for functions returning nothing and parameters.

The #define directive replaces MAX with 10 during preprocessing. So x = 10 and output is 10. (Note: semicolon after MAX is not needed but doesn't affect the output)

All three functions can read strings, though gets() is deprecated due to security issues. fgets() is safer as it limits input size.

sizeof(arr) gives total size of array. sizeof(arr[0]) gives size of one element. Dividing gives the number of elements: $\frac{20}{4}$ = 5.

Both syntaxes are correct. C allows initializing 2D arrays with or without explicit braces for each row.

Integer division truncates the decimal part. $\frac{5}{2}$ = 2 (not 2.5) because both operands are integers.

getchar() reads a single character from standard input (stdin) and returns its ASCII value.

The == operator compares values. Since a and b both have value 5, the condition is true and "Equal" is printed.