C# Control Flow Statements – Interview Questions

1. What is the difference between if-else, switch, and the ternary operator?

All three are used for decision-making in C#, but they are suitable for different situations.

Differences

Simple Example

int marks = 75;

// if-else
if (marks >= 50)
    Console.WriteLine("Pass");
else
    Console.WriteLine("Fail");

// switch
switch (marks)
{
    case >= 50:
        Console.WriteLine("Pass");
        break;

    default:
        Console.WriteLine("Fail");
        break;
}

// Ternary
string result = marks >= 50 ? "Pass" : "Fail";
Console.WriteLine(result);

Output (all three): Pass

Explanation

• if-else: Checks whether marks are greater than or equal to 50.

• switch: Matches the marks against a relational pattern.

• Ternary: Returns "Pass" or "Fail" based on the condition.

Key Points

• Use if-else for complex conditions.

• Use switch when selecting among multiple cases.

• Use the ternary operator for simple conditional assignments.

• Avoid nested ternary operators when they reduce readability.

2. What is the difference between for, foreach, while, and do-while?

All four are looping statements used to execute code repeatedly.

Differences

Simple Example

// for
for (int i = 1; i <= 3; i++)
    Console.WriteLine(i);

// foreach
int[] numbers = { 1, 2, 3 };

foreach (int number in numbers)
    Console.WriteLine(number);

// while
int x = 1;

while (x <= 3)
    Console.WriteLine(x++);

// do-while
int y = 1;

do
{
    Console.WriteLine(y++);
}
while (y <= 3);

Output (each loop):

1
2
3

Explanation

• for: Runs three times using a counter.

• foreach: Reads each element from the array.

• while: Checks the condition before executing.

• do-while: Executes first, then checks the condition.

Execution Flow

for / while
    |
Check Condition
    |
    +-- True  → Execute → Repeat
    |
    +-- False → Exit


do-while
    |
Execute
    |
Check Condition
    |
    +-- True  → Repeat
    |
    +-- False → Exit

Key Points

• for is best when the number of iterations is known.

• foreach is best for reading collection elements.

• while is useful when the iteration count is unknown.

• do-while always executes at least once.

• foreach does not require manual index management.

3. What is the difference between break, continue, and return?

These statements control the execution flow of loops and methods.

Differences

Simple Example

static void Test()
{
    for (int i = 1; i <= 5; i++)
    {
        if (i == 2)
            continue;

        if (i == 4)
            break;

        Console.WriteLine(i);
    }

    Console.WriteLine("Completed");
}

Output:

1
3
Completed

Explanation

• continue: When i == 2, skips printing 2 and proceeds to the next iteration.

• break: When i == 4, immediately exits the loop.

• return: If we replace break with return, the entire Test() method exits, so "Completed" will not print.

Execution Flow

Loop
 |
 +-- continue → Skip current iteration
 |               |
 |               +→ Next iteration
 |
 +-- break    → Exit loop
 |               |
 |               +→ Continue after loop
 |
 +-- return   → Exit entire method

Key Points

• break terminates the nearest enclosing loop or switch.

• continue skips the remaining statements in the current loop iteration.

• return exits the current method immediately.

• return can also return a value to the calling method.

• In nested loops, break exits only the innermost loop.

Quick Interview Revision

Interview Tip: The most commonly tested differences are while vs do-while, for vs foreach, and break vs continue vs return.