To construct a pyramid with uses of alphabets. Would you propose any better solution?
General Observations
The code works as long as the user puts in correct limited values.
The indentation is a little off.
You can decrease the vertical spacing quite a bit, most of the blank lines aren't necessary.
Answers

Will I face any problem for some conditions?

If a user enters a negative number or a number greater than 100 this program will have problems with indexing. Always check user input for correctness and possible error conditions. The program will actually have problems if a user enters a number greater than 52 because there are only 26 letters in the alphabet.

How can I simplify my solution?.

You could break the program up into functions, it's not quite necessary with a program this simple, but it is getting close. Two obviously separate functions that could be implemented right now are get_and_validate_user_input() and print_pyramid(). While functions might seem to make the program more complex and longer each function would be a simpler implementation and building block of the overall implementation.

Is it possible to solve this problem without using an array? Then what will be the strategy?.

Yes. It would be possible to treat the numbers as a value in a range between 'A' and 'Z'.
One Declaration Per Line
This line in the code could cause problems in maintenance in a larger program
int space,num_of_rows,p=1,t=0;

Break it up into 3 lines and always initialize variables in C.
int space = 0;
int num_of_rows = 0;
int p = 1;
int t = 0;