Contents :

  CHAR, RdChar(), WrChar(), string, WrStr(), RdStr().

Exercises :

• (D1) From character to string.
• (S1) Search & Replace.
• (S2) Cryptography (geheimschrift).
• (S3) Palindrome
• (X1) Cryptography II
• (H1) Fill.
• (H2) Cryptography III (geheimschrift).
• (T1) Output
• (T2) Output 2
  

D1: From character to string.

• Define a character variable a. Ask the user for a character.
• Define a word (string) as an array of 10 characters. Ask the user for a word.
• If the second character of the word is a vowel, change it to the given character (variable a).
• Print out the array, letter by letter.

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S1: Search & Replace.

1. Ask the user for a word (of maximal 30 characters) and a letter. Search for the letter in the word and print out the index's when found. Also print the number of appearances (het aantal keren dat de letter voorkomt).
2. Replace in the word the given letter by a 'z'. Print out the resulting word.

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S2: Cryptography (geheimschrift)

• Decypher the above sequence of numbers (copy the code below into your program):

• with the following code:
• each number of the sequence corresponds to a character, the transformed sequence results in a sentence.
• the corresponding character c of a number x is calculated as follow:
• The modulo 34 of x gives you the startindex s.
• If s is greater than 27, then the character is a punctuation mark (leesteken) at index s in decodeArray (c := decodeArray[s];).
• If the original number x is divisible by 3, the corresponding character is the first vowel in decodeArray AFTER the calculated startindex s.
• If x is not divisible by 3, it is the first consonant after s.
• decodeArray := "azertyuiopqsdfghjklmwxcvbna.,!2 :;";
• Hints:
• Thus, the number 38 results in the letter 't' (= first consonant (38 is not divisible by 3) after index 4 (=38 MOD 34)), the number 30 in a '!'.
• You'll have 3 arrays:
• code (array of cardinals) with the sequence of numbers to decypher
• decodeArray (array of 34 chars) with the decode key.
• result (array of chars): here you put the decoded letters (one for each number of code)


Question: the Chinese coder made 1 typical type error! Correct the code array.
 

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S3: Palindrome.

• madam
• neppen
• taartstraat

X1: CryptographyII

• write a program that codes a given sentence with the code of H2.
• for die-hards (much more difficult): write a program that codes a given sentence with the code of S2.
• hint: use the solution of H2/S2 to test your coder

H1: Fill.

• Ask the user for a letter until he enters the letter 'o'.
• put a RdLn(); after the RdChar();   (see for explanation)
  
• Fill an array of size 20 repetively with the letters, until the array is full.
• Print out the resulting string.
• eg: user enters 'a', 'b', 'c', 'o'  =>  output is "abcabcabcabcabcabcab".
• Remark: the shortest solution contains 8 lines of statements (1 statement per line, only multiple read & write statements are allowed on the same line).

H2: Cryptography III (geheimschrift).

• Decypher the next sequence of numbers (copy the code below into your program)
• code[1] := 13; code[2] := -5; code[3] := 31; code[4] := -8; code[5] := 12;

code[6] := -9; code[7] := 22; code[8] := -14; code[9] := 39; code[10] := -20;
code[11] := 23; code[12] := 6; code[13] := 26; code[14] := -20; code[15] := 29;
code[16] := -22; code[17] := 54; code[18] := -34; code[19] := 35; code[20] := -22;
code[21] := 25; code[22] := 7; code[23] := -6; code[24] := 38; code[25] := -34;
code[26] := 37; code[27] := -36; code[28] := 55; code[29] := -23; code[30] := 43;
code[31] := -34; code[32] := 47; code[33] := -40; code[34] := 59; code[35] := -58;
code[36] := 89; code[37] := -57; code[38] := 67; code[39] := -63; code[40] := 72;
code[41] := -57; code[42] := 61; code[43] := -60; code[44] := 80; code[45] := -50;
code[46] := 82; code[47] := -76; code[48] := 85; code[49] := -78; code[50] := 110;
code[51] := -109; code[52] := 113; code[53] := -110; code[54] := 142; code[55] := -128;
code[56] := 129; code[57] := -103; code[58] := 108; code[59] := -107; code[60] := 119;
code[61] := -114; code[62] := 122; code[63] := -99; code[64] := 129;
 
• with the following code:
• each number of the sequence except the first (!) corresponds to a character, the transformed sequence results in a sentence.
• decodeArray is the key table for the decoding...
• decodeArray := "azertyuiopqsdfghjklmwxcvbna.,!2 :;";
• the corresponding character c of a number x is calculated as follow:
• sum x with the previous number of the sequence, this sum gives you the index in the decodeArray of the character c.
• Hints:
• Thus the first letter is a 'i', because code[2] (= 13) + the previous code[1] (= -5) gives 8, and the 8th letter in de decodeArray is a 'i'.
• You'll have 3 arrays:
• code (array of cardinals) with the sequence of numbers to decypher
• decodeArray (array of 34 chars) with the decode key.
• result (array of chars): here you put the decoded letters (one for each number of code, minus the first)

T1: Output

• What is the output of the following program? Calculate in it on paper!!

    CONST STRING_SIZE = 30;          (* constants *)

    VAR
      str, strCopy: ARRAY[1..STRING_SIZE] OF CHAR;            (* variable-declarations *)
      i:CARDINAL;
BEGIN
    WrLn;
    str := "this is Modula2!";

    FOR i := 1 TO 4 DO
      strCopy[i] := str[i+5];
      str[i+3] := str[i];
    END;

    i := 1;
    REPEAT
      IF i < 3 THEN
        str[i] := strCopy[i];
      END;
      i := i + 1;
    UNTIL (str[i] = '!');
    str[i] := "?";
    WrStr(str);
    WrLn;

END T1.

• There are 2 errors in the unreadable result sentence. Try to correct these to get a readable sentence, only 2 numbers has to be changed in the above code. Run the code to test if it works!

T2: Output 2

• What is the output of the following program? Calculate in it on paper!!

• What is the output of the following program? Calculate in it on paper.

• Op de 2 lijnen met (* xx *) wil ik in feite de waarden van arr1[i] en arr2[i] onderling verwisselen. Wat moet ik aan de code veranderen om dit te verkrijgen