“Introduction to Programming With Java” Lecture - 6 U MESH P ATIL

‘switch’ construct Introduction to Arrays Contents for Today’s Lecture

class print_num { public static void main(String args[]) { int a_number; a_number = 0; if(a_number = = 1) System.out.println("One"); else { if(a_number = = 2) System.out.println("Two"); else { if(a_number = = 3) System.out.println("Three"); else System.out.println("No. is out of the range"); } } } } ‘if-else’ Program

class print_num_switch { public static void main(String args[]) { int a_number; a_number = 3; switch(a_number){ case 1: System.out.println("One"); break; case 2: System.out.println("Two"); break; case 3: System.out.println("Three"); break; default: System.out.println("No. is out of the range"); } } } ‘switch’ Program

switch(expression){ case value1: statements; break; case value2: statements; break;.. case valueN: statements; break; default: statements; } Syntax

The case values can be compared only for equality with the switch expression The expression must be of type int, char, short, byte Each case value must be a constant, not a variable Duplicate case values are not allowed The default part is optional Note

Definition: An array is a group/collection of variables of the same type that are referred to by a common name and an index Examples: Collection of numbers Collection of names Collection of suffixes Arrays

Array of numbers: Array of names: Array of suffixes: Examples ment tion ness ves Sholay Shaan Shakti

Array is like a pen box with fixed no. of slots of same size. Analogy

Declaration of array variable: data-type variable-name[]; eg. int marks[]; This will declare an array named ‘marks’ of type ‘int’. But no memory is allocated to the array. Allocation of memory: variable-name = new data-type[size]; eg. marks = new int[5]; This will allocate memory of 5 integers to the array ‘marks’ and it can store upto 5 integers in it. ‘new’ is a special operator that allocates memory. Syntax

Accessing elements in the array: Specific element in the array is accessed by specifying name of the array followed the index of the element. All array indexes in Java start at zero. variable-name[index] = value; eg. marks[0] = 10; This will assign the value 10 to the 1 st element in the array. ; And marks[2] = 863; This will assign the value 863 to the 3 rd element in the array. Syntax…

STEP 1 : (Declaration) int marks[]; marks  null STEP 2: (Memory Allocation) marks = new int[5]; marks  marks[0] marks[1] marks[2] marks[3] marks[4] STEP 3: (Accessing Elements) marks[0] = 10; marks  marks[0] marks[1] marks[2] marks[3] marks[4] Example

class try_array { public static void main(String args[]) { int marks[]; marks = new int[3]; marks[0] = 10; marks[1] = 35; marks[2] = 84; System.out.println(“Marks obtained by 2 nd student=” + marks[1]); } Program

Arrays can store elements of the same data type. Hence an int array CAN NOT store an element which is not an int. Though an element of a compatible type can be converted to int and stored into the int array. eg. marks[2] = (int) 22.5; This will convert ‘22.5’ into the int part ‘22’ and store it into the 3 rd place in the int array ‘marks’. Array indexes start from zero. Hence ‘marks[index]’ refers to the (index+1) th element in the array and ‘marks[size-1] refers to last element in the array. eg. marks[0] refers to 1 st element, marks[1] refers to 2 nd element… etc. etc. Note

Combined declaration & memory allocation: data-type variable-name[] = new data-type[size]; eg. int marks[] = new int[5]; This will declare an int array ‘marks’ and will also allocate memory of 5 integers to it. Combined declaration, allocation & assignment: data-type variable-name[] = {comma-separated values}; eg. int marks[] = {10, 35, 84, 23, 5}; This will declare an int array ‘marks’, will allocate memory of 5 integers to it and will also assign the values as- marks  marks[0] marks[1] marks[2] marks[3] marks[4] Alternative Syntax

1.Write a program that uses two arrays of size 5. One string array for storing names of students and one int array for storing marks obtained by the students. Assign values to the elements in the arrays. Print names and marks of students who have scored more than 35 marks. 2.Write a program same as the above, but don’t use numbers (like 0, 1, 2…etc) to access the elements in the array. Declare an int variable ‘i’ and use it as an index into the arrays. Assignment

Thank you… End