A practical introduction to Pascal programming language - GIARA

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Data structures str(num,w) - Stores in the variable w the text representation of num, where num is anynumeric (real or integer) variable. val(w,num,cod) - Stores in the numeric variable num the value represented by the stringw. In case the string w represents a number, the variable cod takes value 0, but if some erroroccurred cod takes a value other than 0. pos(w1,w2) - Find the first position at which w1 contains w2, if any. In case w2 does notappear in w1, the function returns the value 0. copy(w,pos,len) - Creates a new string that contains len chars of the string w starting atposition pos.Considering all the functionalities they offer, very often it is more practical to use stringsinstead of arrays of chars when handling sentences or words. However, note that string canonly hold lines of text, and cannot be used to substitute arrays of chars with more than onedimension (e.g. 2D matrices).4.3 Exercises4.3.1 Working with arrays and matricesExercise 4.1. Create a program that reads a vector of N positions (being N a constant) and displayits contents.□When the length of an array is known (and that is the case for the exercises in this book),the best way to go through its positions is using a for statement. Note that we define the rangeof the iteration using as limit value the constant previously declared, so that any change in thevalue of the constant does not invalidate the existing code.Program 76: Exercise 4.1program c04e01;constN=10;typerealVector=ARRAY[1..N] OF real;vari:integer;myVector:realVector;begin(* 1- Reading the vector *)writeln(’About to start’);for i:=1 to N dobeginwrite(’Enter value ’,i,’: ’);readln(myVector[i]);end;(* 2- Displaying the values *)writeln(’The contents of the vector are:’);for i:=1 to N dowriteln(’At pos ’,i,’: ’,myVector[i]:4:3)end.⊡67
A Practical Introduction to Pascal Programming LanguageExercise 4.2. Create a program that reads two vectors of N elements (being N a constant) andcalculates their scalar product. Each vector must be read at one single line, in which the user hasto input N numbers split by blank spaces.□This exercise brings forward two different tasks: reading several values in the same lineand computing the scalar product of two vectors. For the former one, we have to use theread command, which reads all the consecutive digits until the user inputs a blank space, thencombines them to create a number. Since the read is enclosed in for construction, the process isrepeated as many as N times. In this way, the use does not need to be asked for several numbersone after another, alleviating the work of inputing a long sequence of numbers. Regarding theformer, we only need an accumulating variable that increasingly sums the product of the elementsin the vectors.Program 77: Exercise 4.2program c04e03;constN=5;typerealVector=ARRAY[1..N] OF real;vari:integer;vecA,vecB:realVector;result:real;begin(* Reading the first vector *)writeln(’Introduce the first vector of ’,N,’ elements, splitted by blank spaces.’);for i:=1 to N doread(vecA[i]);(* Reading the second one *)writeln(’Introduce the second vector of ’,N,’ elements, splitted by blank spaces.’);for i:=1 to N doread(vecB[i]);(* Initializing the variable and computing the result *)result:=0;for i:=1 to N doresult:=result+vecA[i]*vecB[i];(* Displaying the result *)writeln(’The result is ’,result:3:3,’.’)end.⊡Exercise 4.3. Create a program that reads a matrix of N × N integers (being N a constant) anddisplays its elements.□Working with matrices or, in a general way, with d-dimensional arrays is not problematic. Inthis case, we use a double combination of indices for accessing the values, so that the first onerepresents the row, and the second one points out the column. Note that declaring a type for thematrix is not strictly necessary, but enhances slightly the readability of the program68
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A Practical Introduction to Pascal
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ContentsIntroduction to this book 9
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Guidelines and structureThis book i
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