C Programming Fundamentals Flashcards

Question 1

What is the role of the main function in a C program?

Accepted Answer

The main function is the entry point where execution of a hosted C program begins. The runtime environment calls it after startup code prepares the program. Its conventional signature is int main void or int main with argc and argv parameters, and it returns an integer status to the operating system.

Question 2

What does the preprocessor do before the compiler translates a C source file?

Accepted Answer

The preprocessor processes lines beginning with a hash symbol before compilation proper begins. It performs file inclusion through include directives, macro replacement through define directives, and conditional compilation through directives like if and endif. Its output is a single translation unit that the compiler then parses.

Question 3

Why does a header file usually contain declarations rather than full function definitions?

Accepted Answer

Headers are included in many source files, so full definitions placed there would duplicate code across translation units. Declarations tell each file the names, types, and signatures of functions and variables defined elsewhere. Definitions belong in one source file, and include guards stop a header from being processed twice in the same unit.

Question 4

What are the four main stages that turn C source code into an executable program?

Accepted Answer

The four stages are preprocessing, compilation, assembly, and linking. Preprocessing expands directives and macros into expanded source text. Compilation translates that text into assembly or intermediate code and checks syntax and types. Assembly converts generated assembly into object files containing machine code. Linking combines object files and libraries into one executable.

Question 5

What is the difference between a compiler warning and a compiler error?

Accepted Answer

A compiler error stops translation of the affected code, so the program cannot build successfully. A warning reports suspicious code that is still legal C, and compilation usually continues. Enabling a broad warning set in the compiler helps catch mistakes early, even though warnings do not stop the build by default.

Question 6

What does the linker resolve when it combines object files into an executable?

Accepted Answer

The linker resolves external symbol references, matching each function or global variable used in one file with its definition in another. It also incorporates code from libraries that the program depends on. If a referenced symbol has no definition, the linker reports an undefined reference error and does not produce an executable.

Question 7

Why should you specify a C language standard when compiling a program?

Accepted Answer

Specifying a standard tells the compiler which language rules to enforce, so code behaves consistently across different compilers and platforms. Without it, compilers may default to a particular dialect with extensions that other tools reject. Choosing a standard early also prevents accidental reliance on features that are not portable.

Question 8

How would you check the exit status of a C program after it runs in a shell?

Accepted Answer

You check it by printing the shell's status variable right after the program finishes. The shell stores the value returned from main, or passed to exit, in that variable. On common POSIX shells, echoing the variable prints the status. By convention zero means success and any nonzero value signals failure.

Question 9

What is the difference between a variable and a constant in C?

Accepted Answer

A variable is a named storage location whose value can change during program execution. A constant is a value that cannot be modified once defined, which can be declared with the const qualifier or introduced through a macro. Constants help communicate intent and protect values from accidental changes.

Question 10

What are the main kinds of arithmetic types in C?

Accepted Answer

The arithmetic types in C fall into two main kinds, integer types and floating-point types. Integer types hold whole numbers such as int, short, long, and their unsigned forms. Floating-point types such as float and double store approximate real numbers using a sign, exponent, and significand.

Question 11

Why does the size of an int depend on the platform rather than being fixed?

Accepted Answer

The C standard sets only minimum ranges for basic integer types, not exact sizes, so each implementation chooses a width suited to its hardware. An int must be able to represent at least a specified minimum range, but it may be wider. For exact widths, programmers use fixed-width types from the standard integer header.

Question 12

What is the purpose of the sizeof operator, and what type does it produce?

Accepted Answer

The sizeof operator yields the size in bytes of a type or an expression, computed at compile time in most cases. Its result has the unsigned integer type size_t, defined in the standard library headers. Because sizeof is an operator rather than a function, parentheses are needed only when applied to a type name.

Question 13

What is the difference between signed and unsigned integer types in C?

Accepted Answer

A signed integer type can represent both negative and positive values, while an unsigned type represents only zero and positive values. For the same width, an unsigned type holds a larger maximum value. Unsigned arithmetic wraps around modulo a power of two, whereas signed overflow is undefined behavior in C.

Question 14

What does the char type represent in C, and is it always signed?

Accepted Answer

The char type is an integer type large enough to hold any member of the basic execution character set, and it is commonly used for individual characters and small byte values. Whether plain char is signed or unsigned is implementation-defined. Programs that depend on its sign should declare signed char or unsigned char explicitly.

Question 15

What is an enumeration, and why do programmers use it for related named constants?

Accepted Answer

An enumeration defines a type whose values are a set of named integer constants, declared with the enum keyword. Each name receives an integer value, starting at zero by default unless you assign one. Programmers use enumerations to group related values, such as states or menu options, which reads better than bare numbers.

Question 16

What value does an uninitialized local variable hold in C?

Accepted Answer

An uninitialized local variable has an indeterminate value, so reading it before assigning a value causes undefined behavior. Its contents are whatever bytes previously occupied that memory location. Variables with static storage duration, by contrast, are zero-initialized automatically before execution begins in the program.

Question 17

What is the difference between the assignment operator and the equality operator in C?

Accepted Answer

The single equals sign performs assignment, storing the value on its right into the object on its left. The double equals sign compares two values, yielding one if equal and zero otherwise. Mixing them up is a common error, and writing if x = 1 instead of if x == 1 compiles but misbehaves.

Question 18

How does integer division differ from floating-point division in C?

Accepted Answer

When both operands are integer types, division discards any fractional part and truncates the result toward zero. When at least one operand is floating-point, the operation is performed in floating-point and keeps the fraction. For example, 7 / 2 yields 3, while 7 / 2.0 yields 3.5.

Question 19

What does operator precedence determine, and how can parentheses change the result?

Accepted Answer

Operator precedence determines which operators group first when an expression contains several operators without grouping. Multiplication binds more tightly than addition, so 2 + 3 * 4 equals 14. Parentheses override the default order, so writing (2 + 3) * 4 produces 20. Associativity resolves ties between operators of equal precedence.

Question 20

What is short-circuit evaluation in the logical AND and OR operators?

Accepted Answer

Short-circuit evaluation means the right operand of && or || is evaluated only when the left operand does not already determine the result. For &&, a false left operand makes the whole expression false, so the right side is skipped. For ||, a true left operand skips the right side.

Question 21

What does the increment operator produce differently in prefix and postfix form?

Accepted Answer

Prefix increment increases the variable first and yields the new value, while postfix increment yields the old value and then increases the variable. For example, if n is 5, the expression ++n yields 6, but n++ yields 5. In both forms the variable ends up incremented by one.

Question 22

Why is modifying the same variable twice in one expression considered undefined behavior?

Accepted Answer

Modifying the same object more than once within an expression without an ordering between the changes produces undefined behavior in C. For example, i = i++ + 1 changes i twice without a guaranteed order. Compilers may produce different results, so such code should be split into separate statements.

Question 23

What is the purpose of the conditional operator, and how is it written?

Accepted Answer

The conditional operator selects one of two expressions based on a condition, providing a compact alternative to a simple if-else statement. It is written as condition ? first : second. For example, max = a > b ? a : b assigns the larger value to max.

Question 24

How does the comma operator evaluate its operands, and where is it commonly used?

Accepted Answer

The comma operator evaluates its left operand, discards that value, then evaluates the right operand, whose value becomes the result of the whole expression. It is most often used in for loop headers to update several variables at once. Elsewhere it is less common.

Question 25

How does a while loop differ from a do while loop in C?

Accepted Answer

A while loop tests its condition before each iteration, so its body may run zero times. A do-while loop executes its body first and then tests the condition, guaranteeing at least one execution. Both loops continue as long as the condition evaluates to nonzero, and both require careful updating to avoid infinite loops.

Question 26

What does the break statement do inside a loop, and how does continue differ?

Accepted Answer

The break statement exits the innermost enclosing loop or switch immediately, transferring control to the statement after it. The continue statement skips the rest of the current iteration and proceeds to the next evaluation of the loop condition. Unlike break, continue does not end the loop itself.

Question 27

What is the purpose of a switch statement, and why is break often needed inside it?

Accepted Answer

A switch statement compares an integer expression against several constant case labels and jumps to the matching one. Without a break, execution falls through into the following case, which is occasionally intentional but more often a bug. A default label handles values that match no case.

Question 28

How does a function prototype help the compiler check calls to that function?

Accepted Answer

A prototype declares the function's return type, name, and parameter types before any call appears. With this information, the compiler can verify that each call supplies the correct number and types of arguments. It can also convert arguments to the declared parameter types, which prevents errors when calling a function before its definition.

Question 29

What is the difference between passing arguments by value and passing by pointer in C?

Accepted Answer

C always passes arguments by value, meaning the function receives a copy of each argument. Changes to that copy do not affect the caller's variable. To let a function modify the caller's object, you pass the address of that object as a pointer, and the function dereferences it to write through.

Question 30

What does the void return type indicate in a function declaration?

Accepted Answer

The void return type indicates that the function does not produce a value for its caller. Such a function is called for its side effects, such as printing output or updating global state. Using the value of a void call is an error, because there is nothing to use.

Question 31

What is scope in C, and how do block scope and file scope differ?

Accepted Answer

Scope is the region where an identifier can be referred to by name. A variable with block scope is visible only inside the braces where it is declared, along with nested blocks. A variable with file scope, declared outside any function, is visible from its declaration to the end of the translation unit.

Question 32

How does a recursive function avoid running forever, and what is the base case?

Accepted Answer

A recursive function avoids infinite recursion by checking a base case, a condition under which it returns a result without calling itself again. Each recursive call must move the problem closer to that base case. For example, factorial returns one when its argument is zero.

Question 33

What is an array in C, and how are its elements laid out in memory?

Accepted Answer

An array is a fixed-size sequence of objects of the same type, stored contiguously in memory. Elements are accessed by zero-based index, so the first element has index zero. Consecutive elements sit at adjacent addresses separated by the size of the element type, which allows arithmetic on addresses.

Question 34

What happens when a C program accesses an array element beyond its bounds?

Accepted Answer

Accessing an element outside the declared bounds causes undefined behavior, which means the language places no requirement on the result. The program might crash, silently read garbage, or appear to work until later. C does not check array bounds at runtime, so the responsibility lies with the programmer.

Question 35

How is a string represented in C, and what marks its end?

Accepted Answer

A string in C is an array of char terminated by a null character, which is a byte with value zero. The terminator is counted in the array size but is not part of the visible text. Standard library functions such as strlen rely on this terminator to find where the string ends.

Question 36

What does a pointer store, and what does the unary asterisk operator do with it?

Accepted Answer

A pointer stores the address of an object of a particular type. The unary asterisk, called the indirection operator, accesses the object at that stored address, both to read and to write it. The ampersand operator does the reverse by producing the address of an object.

Question 37

How does pointer arithmetic on an array pointer depend on the element type?

Accepted Answer

Adding an integer n to a pointer advances it by n times the size of the pointed-to type, not by n bytes. For example, if p points to an int array, p + 2 points two elements ahead. Subtracting two pointers into the same array yields the number of elements between them.

Question 38

What does malloc return, and why must the result be checked before use?

Accepted Answer

The malloc function returns a pointer to a block of uninitialized memory of the requested size, or a null pointer if the allocation fails. Because allocation can fail when memory is limited, the program must test for null before dereferencing. Memory from malloc is uninitialized and must later be released with free.

Question 39

What is a common cause of a memory leak in a C program?

Accepted Answer

A memory leak occurs when allocated memory becomes unreachable without being freed, often because the only pointer to it was overwritten or went out of scope. A common cause is returning early from a function before calling free. Leaks accumulate over time, eventually exhausting available memory in long-running programs.

Question 40

Why is it dangerous to use a pointer after the memory it refers to has been freed?

Accepted Answer

After free, the pointer still holds the old address, but the object's lifetime has ended, so accessing it causes undefined behavior. The memory may be reused for another allocation, so reads may return unrelated data and writes may corrupt that other object. Good practice is to set the pointer to null after freeing it.

C Programming Fundamentals Flashcards

1Program structure and compilation

2Data types, variables, and constants

3Operators and expressions

4Control flow and functions

5Arrays, strings, pointers, and memory

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