The selection process usually consists of 4 rounds, so there are lot many questions.
Written Test: Questions from aptitude, quant, domain etc.
Programming Round: A problem has to be solved; write the code, execute it, get the solution.
Technical Interview: Some questions from programming concepts, about final year project etc.
HR Interview: Tell me about yourself, salary expectation, relocation plans, why IBM? etc.
Some simplest programs that one can prepare are,
WAP to print next to the last word of a sentence, WAP to remove the vowels from the input string, WAP to convert uppercase to lower case and vice versa of a given string or sentence, WAP to print the desired character from string, WAP to reverse a string etc.