string s = "Just a random string in C#.";

string pattern = @"(?i:\bC#\b)";
Match match = Regex.Match(s, pattern);
// Doesn't work
// I also tried:
// @"(?i:\bC\#\b)" escaping #
// @"(?i:\bC\u0023\b)" using unicode

// But same pattern works for any other alphabetical word
string pattern2 = @"(?i:\brandom\b)";
Match match2 = Regex.Match(s, pattern2);

string s = "Just a random string in C#.";

string pattern = @"(?i:\bC#\b)";
Match match = Regex.Match(s, pattern);
// Doesn't work
// I also tried:
// @"(?i:\bC\#\b)" escaping #
// @"(?i:\bC\u0023\b)" using unicode

// But same pattern works for any other alphabetical word
string pattern2 = @"(?i:\brandom\b)";
Match match2 = Regex.Match(s, pattern2);

string s = "We are living in a <upcase>yellow submarine</upcase>. We don't have <upcase>anything</upcase> else.";
string startTag = "<upcase>";
string endTag = "</upcase>";

// I want it to match:
// 1. <upcase>yellow submarine</upcase>
// 2. <upcase>anything</upcase>

// This pattern match nothing
string pattern = $@"(?'startTag'\s*{startTag})" + $@"(?'text'.*(?!{endTag}))" + $@"(?'endTag'{endTag})";

// This pattern match till last endTag instead for first endTag after the startTag:
// 1. <upcase>yellow submarine</upcase>. We don't have <upcase>anything</upcase>
string pattern = $@"(?'startTag'\s*{startTag})" + $@"(?'text'.*)" + $@"(?'endTag'{endTag})";

MatchCollection matches = Regex.Matches(s, pattern);

string s = "We are living in a <upcase>yellow submarine</upcase>. We don't have <upcase>anything</upcase> else.";
string startTag = "<upcase>";
string endTag = "</upcase>";

// I want it to match:
// 1. <upcase>yellow submarine</upcase>
// 2. <upcase>anything</upcase>

// This pattern match nothing
string pattern = $@"(?'startTag'\s*{startTag})" + $@"(?'text'.*(?!{endTag}))" + $@"(?'endTag'{endTag})";

// This pattern match till last endTag instead for first endTag after the startTag:
// 1. <upcase>yellow submarine</upcase>. We don't have <upcase>anything</upcase>
string pattern = $@"(?'startTag'\s*{startTag})" + $@"(?'text'.*)" + $@"(?'endTag'{endTag})";

MatchCollection matches = Regex.Matches(s, pattern);

string pattern = "."; // Match every character except new line

string pattern = "."; // Match every character except new line

// Array A[] has the items to sort; array B[] is a work array.
void TopDownMergeSort(A[], B[], n)
{
    CopyArray(A, 0, n, B);           // one time copy of A[] to B[]
    TopDownSplitMerge(A, 0, n, B);   // sort data from B[] into A[]
}

// Split A[] into 2 runs, sort both runs into B[], merge both runs from B[] to A[]
// iBegin is inclusive; iEnd is exclusive (A[iEnd] is not in the set).
void TopDownSplitMerge(B[], iBegin, iEnd, A[])
{
    if (iEnd - iBegin <= 1)                     // if run size == 1
        return;                                 //   consider it sorted
    // split the run longer than 1 item into halves
    iMiddle = (iEnd + iBegin) / 2;              // iMiddle = mid point
    // recursively sort both runs from array A[] into B[]
    TopDownSplitMerge(A, iBegin,  iMiddle, B);  // sort the left  run
    TopDownSplitMerge(A, iMiddle,    iEnd, B);  // sort the right run
    // merge the resulting runs from array B[] into A[]
    TopDownMerge(B, iBegin, iMiddle, iEnd, A);
}

//  Left source half is A[ iBegin:iMiddle-1].
// Right source half is A[iMiddle:iEnd-1   ].
// Result is            B[ iBegin:iEnd-1   ].
void TopDownMerge(B[], iBegin, iMiddle, iEnd, A[])
{
    i = iBegin, j = iMiddle;
 
    // While there are elements in the left or right runs...
    for (k = iBegin; k < iEnd; k++) {
        // If left run head exists and is <= existing right run head.
        if (i < iMiddle && (j >= iEnd || A[i] <= A[j])) {
            B[k] = A[i];
            i = i + 1;
        } else {
            B[k] = A[j];
            j = j + 1;
        }
    }
}

void CopyArray(A[], iBegin, iEnd, B[])
{
    for (k = iBegin; k < iEnd; k++)
        B[k] = A[k];
}

// Array A[] has the items to sort; array B[] is a work array.
void TopDownMergeSort(A[], B[], n)
{
    CopyArray(A, 0, n, B);           // one time copy of A[] to B[]
    TopDownSplitMerge(A, 0, n, B);   // sort data from B[] into A[]
}

// Split A[] into 2 runs, sort both runs into B[], merge both runs from B[] to A[]
// iBegin is inclusive; iEnd is exclusive (A[iEnd] is not in the set).
void TopDownSplitMerge(B[], iBegin, iEnd, A[])
{
    if (iEnd - iBegin <= 1)                     // if run size == 1
        return;                                 //   consider it sorted
    // split the run longer than 1 item into halves
    iMiddle = (iEnd + iBegin) / 2;              // iMiddle = mid point
    // recursively sort both runs from array A[] into B[]
    TopDownSplitMerge(A, iBegin,  iMiddle, B);  // sort the left  run
    TopDownSplitMerge(A, iMiddle,    iEnd, B);  // sort the right run
    // merge the resulting runs from array B[] into A[]
    TopDownMerge(B, iBegin, iMiddle, iEnd, A);
}

//  Left source half is A[ iBegin:iMiddle-1].
// Right source half is A[iMiddle:iEnd-1   ].
// Result is            B[ iBegin:iEnd-1   ].
void TopDownMerge(B[], iBegin, iMiddle, iEnd, A[])
{
    i = iBegin, j = iMiddle;
 
    // While there are elements in the left or right runs...
    for (k = iBegin; k < iEnd; k++) {
        // If left run head exists and is <= existing right run head.
        if (i < iMiddle && (j >= iEnd || A[i] <= A[j])) {
            B[k] = A[i];
            i = i + 1;
        } else {
            B[k] = A[j];
            j = j + 1;
        }
    }
}

void CopyArray(A[], iBegin, iEnd, B[])
{
    for (k = iBegin; k < iEnd; k++)
        B[k] = A[k];
}

if(condition)
{
    code here;
}

if(condition)
{
    code here;
}

if(condition){
    code here;
}

if(condition){
    code here;
}