Strings in C Programming

Strings in C Programming – Complete Guide with MCQs for CDAC C-CAT

If you’re preparing for the CDAC C-CAT exam, GATE, technical interviews, or simply learning C Programming, understanding strings in C is essential.

Unlike languages such as Java, Python, or C++, C does not have a built-in String data type. Instead, a string is represented as an array of characters terminated by a null character ('\0').

Because strings are implemented using arrays and pointers, questions involving strings frequently appear in the CDAC C-CAT, interviews, and university exams.

What is a String in C?

One of the biggest misconceptions among beginners is that String is a data type in C.

It is not.

Unlike Java,

String name = "Anand";

or Python,

name = "Anand"

there is no String data type in C.

Instead, a string is simply an array of characters that ends with a special character called the null terminator ('\0').

For example,

char name[] = "Anand";

is equivalent to

char name[] = {
    'A',
    'n',
    'a',
    'n',
    'd',
    '\0'
};

Notice the compiler automatically adds the null character.

Without it, C would never know where the string ends.

---

How Strings are Stored in Memory

Consider

char name[] = "CAT";

Memory looks like this:

Address

1000      1001      1002      1003

+-----+-----+-----+------+
| 'C' | 'A' | 'T' | '\0' |
+-----+-----+-----+------+

Each character occupies one byte because

sizeof(char) == 1

The null terminator also occupies one byte.

Therefore

char name[] = "CAT";

occupies

3 characters
+1 null character
------------------
4 bytes

Therefore,

sizeof(name)

returns

4

not

3

This is one of the most frequently asked CDAC C-CAT questions.

---

Why is the Null Character Important?

Suppose we write

printf("%s", name);

How does printf() know where to stop?

It simply keeps reading memory until it encounters

'\0'

Example

+----+----+----+----+
| H  | i  | !  |\0 |
+----+----+----+----+

           ^
           printf stops here

If the null character is missing, printf() continues reading memory beyond the array, leading to undefined behavior.

---

Strings are Arrays

Consider

char city[] = "Delhi";

Internally, this is just an array.

Index

0     1     2     3     4     5

+----+----+----+----+----+------+
| D  | e  | l  | h  | i  |\0 |
+----+----+----+----+----+------+

So,

city[0]

returns

'D'

while

city[4]

returns

'i'

and

city[5]

returns

'\0'

---

Every Character is an Integer

People often think characters are special values.

They are not.

Every character is simply an integer represented using the ASCII table.

Example

printf("%d", 'A');

Output

65

Similarly,

printf("%d", 'a');

prints

97

while

printf("%c", 97);

prints

a

Characters and integers are interchangeable because characters are stored using their numeric ASCII values.

---

Did You Know?

This question appears surprisingly often in interviews.

sizeof('A')

Most beginners answer

1

But in C, a character literal has the type int.

Therefore

sizeof('A')

typically returns

4

because it is equivalent to

sizeof(int)

However,

sizeof(char)

always returns

1

Remember this difference.

Expression	Typical Result
sizeof(char)	1
sizeof('A')	4
sizeof(int)	4

Note: This behavior is specific to C. In C++, 'A' has type char, so sizeof('A') is usually 1.

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CDAC C-CAT Tip

Whenever you see a question involving strings, immediately ask yourself:

• Is this an array or a pointer?
• Does it contain a null terminator?
• Is the question about memory or contents?
• Is it comparing addresses or characters?

More than half of tricky C-CAT string questions can be solved correctly by answering these four questions first.

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What’s Next?

Now that you know what a string actually is, the next section explains why the array name is actually the address of the first character, how pointer arithmetic works, and why arr[i] is exactly the same as *(arr+i).

These concepts form the foundation for understanding every function in <string.h>.