Top 35 C Programming Interview Questions and Answers

This question checks your understanding of the basics of the C programming language. 

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C is a versatile, procedural programming language created by Dennis Ritchie at Bell Labs. It’s extensively used in system programming, embedded systems, and applications that demand high performance.

This question tests your knowledge of the origin of the C programming language. 

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The C programming language was developed by Dennis Ritchie in 1972 at Bell Labs. Ritchie designed C as a system programming language to rewrite the UNIX operating system, enhancing its portability and efficiency. 

This question assesses your understanding of the classification of C in terms of abstraction and usage. 

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C is regarded as a mid-level programming language because it blends elements of both high-level and low-level languages. It enables direct manipulation of hardware resources, like assembly language, while also offering high-level programming constructs such as functions and structures. 

This question evaluates your knowledge of the history of the C language. 

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The C programming language was developed by Dennis Ritchie at Bell Labs in 1972 as a successor to the B language. Its creation was motivated by the need for a more robust language to write the UNIX operating system. 

This question tests your understanding of the significance of the C language in programming history. 

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C is often referred to as the mother language because it has significantly influenced many modern programming languages, including C++, Java, and Python. Moreover, it established the groundwork for programming methodologies and compiler design. 

This question checks your understanding of basic input and output functions in C. 

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“printf()” is used for outputting data to the console, while “scanf()” is used for reading input from the console in C. These functions are essential for interacting with users, allowing us to display messages and capture user input.  

This question evaluates your knowledge of naming conventions in C programming. 

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In C, the maximum length of an identifier is 31 characters, although some implementations may support longer names. Identifiers are used to name variables, functions, and other elements in a program. 

This question tests your knowledge of data types in C. 

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The basic data types in C include “int” for integers, “float” for floating-point numbers, “char” for characters, and “double” for double-precision floating-point numbers. Each data type serves a specific purpose and has a different memory requirement.  

This question assesses your understanding of the smallest building blocks in a C program. 

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Tokens in C are the smallest units of a program and include keywords, identifiers, constants, strings, and operators. They are used to construct statements and expressions in the program.  

This question checks your understanding of data structures in C. 

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An array is a collection of elements, all the same data type, stored in contiguous memory locations. In C, arrays allow us to store multiple values under a single variable name, which is useful for handling large amounts of related data. 

This question tests your knowledge of user-defined data types in C. 

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A structure in C is a user-defined data type that allows grouping of variables of different data types under a single name. It is used to represent complex data types that require more than one value to describe them. 

This question checks your understanding of another user-defined data type in C. 

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A union is a user-defined data type like a structure, but in a union, all members share the same memory location. This means only one member can hold a value at a time, making unions efficient for memory management when we need to store one of several possible data types.  

This question evaluates your understanding of modular programming in C. 

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Functions in C are blocks of code that perform specific tasks and can be called multiple times. They promote code reusability and modularity, allowing us to break down complex problems into smaller, manageable pieces. By using functions, we can organise code better and avoid repetition. 

This question assesses your understanding of the key characteristics of C. 

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The key features of C include its simplicity, efficiency, rich set of built-in operators, portability, support for low-level programming, and powerful data handling through pointers. It also provides structured programming, making it easier to debug and maintain code. 

This question tests your knowledge of the recursion concept and how it is implemented in C. 

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Recursion in C is a process where a function calls itself to solve a problem. It is typically used to solve problems that can be broken down into smaller, repetitive tasks, like calculating factorials or performing tree traversals.  

This question checks your understanding of pointers and their special values. 

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A NULL pointer is a pointer that points to nothing or has the value 0. It is often used as a sentinel value to indicate that the pointer does not currently refer to a valid object. Using NULL pointers helps prevent accidental access to invalid memory locations, which can cause runtime errors. 

This question evaluates your knowledge of memory management in C using pointers. 

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A pointer is a variable that stores the memory address of another variable. Pointers are used for dynamic memory allocation, array manipulation, and handling functions. They allow us to directly access and manipulate memory, which can be very efficient, but also requires careful management to avoid errors. 

This question tests your understanding of the practical uses of pointers. 

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Pointers in C are used for a variety of tasks, including dynamic memory allocation, passing arguments by reference to functions, and efficient handling of arrays and strings. They are also essential when dealing with data structures like linked lists and trees, where memory management is critical. 

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This question checks your knowledge of pointers used in older memory models. 

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A far pointer in C is a type of pointer used in older, segmented memory models. It can point to memory outside the current segment, making it capable of accessing memory beyond the current 64KB segment. Far pointers are typically used in DOS-based systems and are rarely seen in modern programming. 

This question evaluates your understanding of the risks associated with pointers. 

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A dangling pointer refers to a pointer that still points to a memory location that has been deallocated or freed. Accessing a dangling pointer can lead to undefined behaviour, such as crashes or memory corruption. Proper memory management and freeing pointers are essential to avoid dangling pointer issues. 

This question tests your knowledge of multi-level pointer references in C. 

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A pointer to pointer is a variable that stores the address of another pointer. It is useful for dynamic memory allocation, where we need to modify the pointer itself from within a function. Pointer to pointer is also frequently used in multidimensional arrays. 

This question assesses your understanding of memory management in C. 

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Static memory allocation refers to the allocation of memory at compile time. Variables with static memory allocation have a fixed memory location throughout the program's execution. This type of memory allocation is used for global and static variables. 

This question checks your knowledge of runtime memory management in C. 

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Dynamic memory allocation allows us to allocate memory during runtime using functions like “malloc()”, “calloc()”, “realloc()”, and “free()”. It is useful when the size of the data structures is not known in advance. Dynamic memory allocation provides flexibility but requires careful memory management to prevent memory leaks. 

This question tests your understanding of C library functions for memory allocation. 

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"The functions used for dynamic memory allocation in C are “malloc()”, “calloc()”, “realloc()”, and “free()”. “malloc()” allocates a block of memory,  “calloc()” allocates and initialises the memory to zero, “realloc()” resizes a memory block, and “free()” deallocates the memory. Proper usage of these functions is crucial for managing heap memory." 

This question evaluates your understanding of dynamic memory allocation functions in C. 

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“malloc()” allocates a block of memory but does not initialise it, whereas “calloc()” allocates and initialises the allocated memory to zero. “calloc()” is often used when memory needs to be pre-initialised, while “malloc()” is faster if initialisation is not required. 

This question tests your programming skills with a basic mathematical algorithm in C. 

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Here’s an example program: 

This program takes an integer input and checks whether the number is divisible by any integer other than 1 and itself. If it finds any divisor, the number is not prime." 

This question evaluates your understanding of variable visibility in C. 

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The scope of a variable in C refers to the region of the program where the variable is accessible. Variables can have local, block, or global scope depending on where they are declared. Understanding scope is crucial to avoid unintended side effects, such as accidentally modifying a global variable from within a function. 

This question checks your understanding of C preprocessor functionality. 

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Preprocessor directives are instructions given to the C preprocessor, which is executed before the compilation of the program. Common directives include “#define”, “#include”, and “#ifdef”. They are used to make the code more modular and flexible, such as including header files or defining constants. 

This question assesses your understanding of parameter passing mechanisms in C. 

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In call by value, a copy of the actual parameter is passed to the function, and modifications made inside the function do not affect the original variable. In call by reference, the address of the actual parameter is passed, and changes affect the original variable. Call by reference is often more efficient for large data structures like arrays. 

This question tests your knowledge of variable types based on their scope. 

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Local variables are declared within a function and are accessible only within that function. Global variables are declared outside all functions and are accessible throughout the entire program. Global variables can be useful for sharing data between functions but overusing them can make code harder to maintain. 

This question checks your understanding of variable lifetimes in C. 

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A static variable in C retains its value between function calls. It is initialised only once, and its value persists for the lifetime of the program. Static variables are useful when we need to keep track of a value across multiple invocations of a function, such as counting the number of times a function is called. 

This question evaluates your knowledge of automatic variables in C. 

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The auto keyword in C is used to declare automatic variables, which are local variables with automatic storage duration. However, the use of auto is implicit, and modern C compilers don't require it to be explicitly mentioned. This keyword is more of historical significance and is rarely used in modern C programming. 

This question assesses your understanding of memory management issues in C. 

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A dangling pointer points to memory that has already been freed, while a memory leak occurs when memory that is no longer needed is not released. In the case of a memory leak, no pointer references the unfree memory, but with a dangling pointer, an invalid reference still exists. Both issues can lead to serious problems such as crashes or resource exhaustion, and proper memory management practices should be followed to avoid them. 

This question tests your understanding of memory optimisation and how C handles variables that can change outside of the program's control. 

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The “volatile” keyword tells the compiler not to optimise the code that involves a particular variable, because its value may change unexpectedly, such as in the case of hardware registers or multi-threaded applications. When a variable is declared as “volatile”, the compiler will always reload its value from memory whenever it is accessed, rather than relying on an optimised copy stored in a register. This is crucial in scenarios where the variable can be modified by external processes, like interrupts or hardware. 

This question assesses your knowledge of non-local jumps and how C handles abnormal control flow. 

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“setjmp()” and “longjmp()” are functions used to perform non-local jumps in C. “setjmp()” saves the program's current state (the stack context) in a buffer for later use, while “longjmp()” restores this saved state and transfers control back to the point where “setjmp()” was called. This mechanism is often used for error handling or recovering from unusual conditions. However, it should be used carefully as it bypasses the normal flow of function calls and can cause resource leaks if not properly handled. 

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