Arrays and Strings in C++

Hello students, welcome to Kwickprep. Your class has forty students. Will you create forty separate variables for their marks? No! Today we learn arrays, which store many values under one name. We will cover one and two dimensional arrays, two kinds of strings, array programs, and passing arrays to functions.

First, what is an array? An array is a group of values that all have the same data type. The values sit side by side in memory, under one name. We reach each value using its position number, called the index or subscript. The index starts at zero, so the last index is always one less than the size.

This array called runs holds the scores of five batters. The number in square brackets is the size, and the values go inside curly braces. Runs of zero is the first score, forty five. Runs of four is the fifth and last score, sixty four. Pause and predict. What happens with runs of five? There is no such element, and C plus plus does not check, so you get a garbage value or a crash.

Picture the array as a row of boxes. Index zero holds forty five, the first element. Index one holds twelve. Index two holds seventy eight, the highest score. Index three holds thirty. Index four holds sixty four, the last element. Index five is outside the array, which is called out of bounds, and it is a serious bug.

Loops and arrays work together. Here the array a holds the five runs. The loop counter goes from zero to four, one index at a time. Each score is added to sum. At the same time, if a score is bigger than big, it becomes the new big. Big starts as the first element, not zero, so it works even for negative numbers. The total is two hundred twenty nine and the highest is seventy eight.

Linear search checks each element one by one until it finds the value. Here we look for roll number twenty one. Pos starts at minus one, which means not found. The loop compares each element with twenty one, using double equals. It is found at index two, which is the third position.

A two dimensional array is a table with rows and columns, like a marks register. The first size is the number of rows, and the second is the number of columns. So marks has two rows of three marks each, one row per student. Marks of one, two means row one, column two. Both start from zero, so it is the second student's third mark, eighty five.

To visit every cell, we use a loop inside a loop. The outer loop picks a row, and the inner loop moves across its columns. For each row, t, the total, starts at zero and adds three marks. The first student's total is two hundred forty. The second student's total is two hundred twenty.

Now strings. A C style string is an array of characters that ends with a special null character, written as backslash zero. Riya has four letters, so she needs five boxes, including the null character. The function string length, from the header C string, counts the letters, so it prints four. You cannot copy these strings with an equals sign, so you use functions like string copy.

Modern C plus plus gives the string class, from the string header. A string grows by itself, so there is no fixed size to worry about. You join strings with plus and copy them with a single equals sign. City plus space City gives Surat City. Its length is ten, because the space also counts.

Let us compare the two kinds of strings. A char array has a fixed size, while a string object grows by itself. A char array must end with the null character, but a string object manages that for you. To copy, a char array needs string copy, while a string just uses equals. To join, use string cat, or simply plus. For length, use string length, or the length function. To compare, use string compare, or simply double equals.

Here is a common trap. See in with the extraction operator stops reading at the first space. So if you type Riya Shah, only Riya is stored. The get line function, from the string header, reads the whole line, including spaces. If you type Riya Shah, this program prints Hello, Riya Shah.

To pass an array to a function, write the parameter with empty square brackets. In the call, write only the array name, with no brackets. The function cannot know the array size, so we also pass the size, here four. Total adds the four marks and returns three hundred.

Here is an important exam point. An array is not copied when passed. The function receives the address of the first element. So any change inside the function changes the original array. Bonus adds five to every mark, and marks of zero in main becomes sixty five. To stop accidental changes, write const before the parameter.

Let us revise what we learned today. An array stores values of the same type under one name, with indexes from zero to size minus one. A two dimensional array has rows and columns, and we visit it with nested loops. A char array string ends with the null character, while a string object grows by itself. Use get line to read a line with spaces. And arrays are passed by address, so a function can change them. Try finding the lowest score in the runs array yourself.