WBBSE Madhyamik Computer Application (Optional): Arrays, Strings and Simple Data Handling

What the examiner tests

Declaring and traversing arrays, computing sum/average/largest, searching, and handling strings with library functions.

Core rules

• An array stores elements of the same type in contiguous memory. int a[5]; creates indices 0 to 4; the last valid index is size − 1.
• Initialise at declaration: int a[5] = {2, 4, 6, 8, 10};. Partial initialisation fills the rest with 0.
• Traversal pattern: for (i = 0; i < 5; i++) - use <, not <=. Accumulate sum = sum + a[i], or update max when a[i] > max.
• For a maximum, initialise max with a[0], not with 0, so arrays of negative numbers work.
• A string is a char array ending with the null character '\0'. char s[6] = "WBBSE"; needs 6 cells: 5 letters plus '\0'.
• string.h functions: strlen (counts characters but not '\0'), strcpy (copy), strcat (join), strcmp (returns 0 when equal). Compare strings with strcmp, never with ==.

Worked example

Linear search in a = {4, 9, 2, 7} for key 7: i = 0: 4 ≠ 7; i = 1: 9 ≠ 7; i = 2: 2 ≠ 7; i = 3: 7 = 7 → found at index 3 after 4 comparisons. If the loop finishes without a match, print “not found”.

Traps

• Accessing a[5] in an array of size 5 - out of bounds.
• Forgetting the '\0' when counting the space needed for a string.
• Using sizeof(s) instead of strlen(s); sizeof includes the terminator and depends on the declared size.
• Using gets(); prefer fgets(), which limits input length.
• Expecting scanf("%s", s) to read a full name containing a space - it stops at whitespace.