How to search for a word in a string in FreeBASIC

Question

I am trying to create an internal function in my FreeBASIC program where i want to check for the word "echo" in the string variable "line0" and if "echo" is part of the string, i want it to echo the input (except "echo")

Answer 1

did you do any kind of research? Sorry, but I assume you did not.

The answer is, there is already a function for this task builtin in Basic language.

The function you are searching for is "INSTR". Please read the available documentation for FreeBasic. If you then decide to try to write your own INSTR function (if you need a feature which is not provided by the builtin function), try to do your coding, and if you stuck, we´ll try to help.

Your described task will therefore include the following functions:

INSTR  ' check if the string is here
LEN    ' to know the length of your search string
MID    ' to create the 'reduced' output (maybe you will to have it used twice)

Answer 2

BASIC's Instr function can search through a string and find out if it contains a certain substring. It can do so starting at the first position of the string or any other position if we mention the value in the parameter list. The result that Instr returns is the character position of the find or else zero to denote that the substring was not found.

It's the optional mentioning of the start position that makes all the difference in writing an algorithm that has to find all occurences of a certain substring.
Once Start = 1 Position = Instr(Start, MyString, MySubString) has found the first substring, we can move the start position to just past the find and start over again. We keep doing so until the Instr function returns zero which tells us there are no more occurences of the substring.

Echo asked: What is this echo that echoes in my ear?
^   ^                    ^   ^     ^   ^            ^
1   |                    |   |     |   |            |
+4  5                    |   |     |   |            |
                         26  |     |   |            |
                         +4  30    |   |            |
                                   36  |            |
                                   +4  40           |
                                                    0 "Not found"

A function that prints its result directly

This SkipText function expects from 1 to 3 parameters. The second and third parameters are optional because of the mention of a default value in the parameter list.

• param1 is the string to search (in)
• param2 is the string to search for
• param3 can limit the number of removals

Declare Function SkipText (a As String, b As String = "", c As Integer = 1) As Integer
Dim As String s

s = "Echo asked: What is this echo that echoes in my ear?"

Print "The function outputs directly"
Print " Unmodified: ";
SkipText(s)
Print " Modified*1: ";
SkipText(s, "echo", 1)
Print " Modified*2: ";
SkipText(s, "echo", 2)
Print " Modified*3: ";
SkipText(s, "echo", 3)

GetKey  ' So you can inspect the output

Function SkipText (a As String, b As String, c As Integer) As Integer

    Dim As Integer h, i, j, k

    h = IIf(c < 1, 1, c)  ' Guard against bogus input
    i = 1
    j = 1 + Len(a) - Len(b)
    Do While i <= j
        k = InStr(i, a, b)  ' Case-sensitive
        If k = 0 Then Exit Do
        Print Mid(a, i, k-i);
        i = k + Len(b)  
        h -= 1
        If h = 0 Then Exit Do
    Loop
    Print Mid(a, i)
    Return 0
End Function

A function that returns a string that the caller can then print

Next SkipText function expects from 1 to 3 parameters. The second and third parameters are optional because of the mention of a default value in the parameter list.

• param1 is the string to search (in)
• param2 is the string to search for
• param3 can limit the number of removals

If you tried the above code snippet, you will have seen that the first "Echo", the one that starts with a capital, was not removed. This happens because FreeBasic's Instr always works 'case-sensitive'. The simple solution to remove in a 'case-insensitive' way is to use the UCase function like in:
Position = Instr(Start, UCase(MyString), UCase(MySubString))

Declare Function SkipText (a As String, b As String = "", c As Integer = 1) As String
Dim As String s

s = "Echo asked: What is this echo that echoes in my ear?"

Print "The function returns a (reduced) string"
Print " Unmodified: "; SkipText(s)
Print " Modified*1: "; SkipText(s, "echo", 1)
Print " Modified*2: "; SkipText(s, "echo", 2)
Print " Modified*3: "; SkipText(s, "echo", 3)

GetKey  ' So you can inspect the output

Function SkipText (a As String, b As String, c As Integer) As String

    Dim As String t = ""
    Dim As Integer h, i, j, k

    h = IIf(c < 1, 1, c)  ' Guard against bogus input
    i = 1
    j = 1 + Len(a) - Len(b)
    Do While i <= j
        k = InStr(i, UCase(a), UCase(b))  ' Case-insensitive
        If k = 0 Then Exit Do
        t = t + Mid(a, i, k-i)
        i = k + Len(b)  
        h -= 1
        If h = 0 Then Exit Do
    Loop
    Return t + Mid(a, i)
End Function

() Because these are tiny code snippets, I wasted no time choosing sensible identifiers. In longer programs you should always pick meaningful names for any identifiers.
() FreeBasic comes with a nice, comprehensive manual. If anything isn't clear, first consult the manual, then maybe ask a question on this forum.