41. Is it possible to have more than one main() function in a C program ?
Ans: The function main() can appear only once. The program execution starts from main.
42. How can we read/write Structures from/to data files?
Ans: To write out a structure we can use fwrite() as Fwrite( &e, sizeof(e),1,fp);Where e is a structure
variable. A corresponding fread() invocation can read the structure back from file. calling fwrite() it writes out sizeof(e) bytes from the address &e. Data files written as memory images with fwrite(),however ,will not be portable, particularly if they contain floating point fields or Pointers. This is because memory layout of structures is machine and compiler dependent. Therefore, structures written as memory images cannot necessarily be read back by programs running on other machine, and this is the important concern if the data files you’re writing will ever be interchanged between machines.
Ans: The function main() can appear only once. The program execution starts from main.
42. How can we read/write Structures from/to data files?
Ans: To write out a structure we can use fwrite() as Fwrite( &e, sizeof(e),1,fp);Where e is a structure
variable. A corresponding fread() invocation can read the structure back from file. calling fwrite() it writes out sizeof(e) bytes from the address &e. Data files written as memory images with fwrite(),however ,will not be portable, particularly if they contain floating point fields or Pointers. This is because memory layout of structures is machine and compiler dependent. Therefore, structures written as memory images cannot necessarily be read back by programs running on other machine, and this is the important concern if the data files you’re writing will ever be interchanged between machines.
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43. what are C tokens? (IMP)
Ans: There are six classes of tokens: identifier, keywords, constants, string literals, operators and other separators.
44. What is preincrement and post increment?
Ans: ++n (pre increment) increments n before its value is used in an assignment operation or any
expression containing it. n++ (post increment) does increment after the value of n is used.
Ans: There are six classes of tokens: identifier, keywords, constants, string literals, operators and other separators.
44. What is preincrement and post increment?
Ans: ++n (pre increment) increments n before its value is used in an assignment operation or any
expression containing it. n++ (post increment) does increment after the value of n is used.
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45. Difference between an array of pointers and a pointer to an array?
Ans:
Array of pointers
1- Declaration is: data_type *array_name[size];
2-Size represents the row size.
3- The space for columns may be dynamically
Pointers to an array
1-Declaration is data_type ( *array_name)[size];
2-Size represents the column size.
46. Discuss on pointer arithmetic?
Ans:
1- Assignment of pointers to the same type of pointers.
2- Adding or subtracting a pointer and an integer.
3-subtracting or comparing two pointer.
4-incrementing or decrementing the pointers pointing to the elements of an array. When a pointer
to an integer is incremented by one , the address is incremented by two. It is done automatically
by the compiler.
5-Assigning the value 0 to the pointer variable and comparing 0 with the pointer. The pointer
having address 0 points to nowhere at all.
47. How are structure passing and returning implemented?
Ans: When structures are passed as arguments to functions, the entire structure is typically pushed on
the stack, using as many words as are required. Some compilers merely pass a pointer to the structure, though they may have to make a local copy to preserve pass-by-value semantics.
Structures are often returned from functions in a location pointed to by an extra,compiler-supplied “hidden” argument to the function. Some older compilers used a special,static location for structure returns, although this made structure-valued functions non-reentrant, which ANSI C disallows.
48. What is a structure?
Ans: Structure constitutes a super data type which represents several different data types in a single unit. A structure can be initialized if it is static or global.
49. What are the differences between structures and union?
Ans: A structure variable contains each of the named members, and its size is large enough to hold all the members. Structure elements are of same size. A union contains one of the named members at a given time and is large enough to hold the largest member. Union element can be of different sizes.
50. In header files whether functions are declared or defined?
Ans: Functions are declared within header file. That is function prototypes exist in a header file,not function bodies. They are defined in library (lib).
Ans:
Array of pointers
1- Declaration is: data_type *array_name[size];
2-Size represents the row size.
3- The space for columns may be dynamically
Pointers to an array
1-Declaration is data_type ( *array_name)[size];
2-Size represents the column size.
46. Discuss on pointer arithmetic?
Ans:
1- Assignment of pointers to the same type of pointers.
2- Adding or subtracting a pointer and an integer.
3-subtracting or comparing two pointer.
4-incrementing or decrementing the pointers pointing to the elements of an array. When a pointer
to an integer is incremented by one , the address is incremented by two. It is done automatically
by the compiler.
5-Assigning the value 0 to the pointer variable and comparing 0 with the pointer. The pointer
having address 0 points to nowhere at all.
47. How are structure passing and returning implemented?
Ans: When structures are passed as arguments to functions, the entire structure is typically pushed on
the stack, using as many words as are required. Some compilers merely pass a pointer to the structure, though they may have to make a local copy to preserve pass-by-value semantics.
Structures are often returned from functions in a location pointed to by an extra,compiler-supplied “hidden” argument to the function. Some older compilers used a special,static location for structure returns, although this made structure-valued functions non-reentrant, which ANSI C disallows.
48. What is a structure?
Ans: Structure constitutes a super data type which represents several different data types in a single unit. A structure can be initialized if it is static or global.
49. What are the differences between structures and union?
Ans: A structure variable contains each of the named members, and its size is large enough to hold all the members. Structure elements are of same size. A union contains one of the named members at a given time and is large enough to hold the largest member. Union element can be of different sizes.
50. In header files whether functions are declared or defined?
Ans: Functions are declared within header file. That is function prototypes exist in a header file,not function bodies. They are defined in library (lib).
