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Example: Replacing leading and trailing characters in a string

Sequencing principles demonstrated​

An extension (a problem solving sequence) which includes a variation (a problem solving sequence).

Prerequisite content​

Prior to asking the learner to solve a problem, the following content is provided.

The following code prints each character, one-by-one, in a string. The code illustrates traversing a string in the forward direction using a for loop.

for (int i = 0; i < txt.length(); i++)
  cout << str[i] // Display the character at position i

Illustrates traversing a string in the backward direction using a for loop.

for (int i = txt.length() - 1; i >= 0; i--)
  cout << str[i] // Display the character at position i

Find the first occurence of "n" in a string​

The following code illustrates using a while loop that runs while two conditions are true. One of them is while the end of the string has not been reached, which is common.

i = 0;
while (index < str.length() && str[index] <> 'n')
  i++;
if (str[index] <> 'n')
  pos = i;
else:
  pos = -1; // "n" not found

Problem​

Replace all leading and trailing spaces in a string with the - character.

Solution​

index = 0
while (index < len(str.length() && string[index] == " ")
 {
    str[index] = "-";
    index++;
    }
index = len(string) - 1
while (index >= 0 && string[index] == " ") {
    str[index] = "-";
    index--;
    }

Sequencing analysis of the solution​

The solution uses an extension, which includes a variation.

The extension​

Two loops are needed. One traverses forward. The other traverses backward. The background info. did not give an example of using two loops in the same program.

The variation​

The background info used while (index < str.length() && str[index] <> 'n'). In the solution, while (index < str.length() && string[index] == " ") is a variation of that.