C

C is a foundational programming language known for speed and direct control over memory. It is widely used in system programming, operating systems, and embedded devices. C programs are written as text files with a .c extension and compiled into machine code using a compiler (like GCC). Clear code in C means careful variable naming, consistent formatting, and commenting logic rather than obvious syntax. This chapter introduces core elements: printf, variables, arithmetic, conditions, loops, functions, arrays, and finishes with a working subtraction calculator as the final example.

Hello world

The classic starter program includes stdio.h for input/output and uses printf.

#include <stdio.h>
int main() {
  printf("Hello, world!\\n");
  return 0;
}

Variables and types

C uses types like int, float, and char. Declaring them clearly avoids confusion. Use scanf to read input but always validate for safety in real programs.

int age = 12;
float height = 4.5;
char initial = 'A';

Conditions

Conditions guide program flow. The braces { } group statements together.

int age = 18;
if (age >= 18) {
  printf("Adult\\n");
} else {
  printf("Minor\\n");
}

Loops

Loops repeat actions. for is commonly used for counting, while for conditions. Keep body short and simple.

for (int i = 0; i < 5; i++) {
  printf("i = %d\\n", i);
}

Functions

Functions group logic for reuse. Declare them before use or place them above main.

int add(int a, int b) {
  return a + b;
}

Final example — calculator for subtraction

The following program reads two numbers, subtracts them, and prints the result. Save this as program.c and compile with gcc program.c -o program before running.

program.c

#include <stdio.h>

int main() {
  double minuend, subtrahend, difference;
  printf("Enter minuend: ");
  scanf("%lf", &minuend);
  printf("Enter subtrahend: ");
  scanf("%lf", &subtrahend);
  difference = minuend - subtrahend;
  printf("Difference: %lf\\n", difference);
  return 0;
}

MCQs

1. Which header file is required to use printf() in C?

(a) stdlib.h

(b) string.h

(d) math.h

► (c) stdio.h

2. What is the correct file extension for a C source file?

(a) .cpp

(b) .c

(d) .java

► (b) .c

3. Which function reads input from the user?

(a) get()

(b) scanf()

(d) input()

► (b) scanf()

4. Which format specifier prints a floating-point value in printf?

(a) %d

(b) %c

(d) %s

► (c) %f

5. What does the return value 0 in main() usually indicate?

(a) Successful execution

(b) Error in program

(d) Nothing special

► (a) Successful execution

6. Which keyword is used to declare a constant value in C?

(a) define

(b) const

(d) fixed

► (b) const

7. What will the condition (5 > 3) evaluate to in C?

(a) 5

(b) 3

(d) true

► (c) 1

8. Which loop is guaranteed to run at least once?

(a) for

(b) while

(d) foreach

► (c) do...while

9. Which operator is used for equality comparison in C?

(a) =

(b) ==

(d) :=

► (b) ==

10. Which array declaration is correct in C?

(a) int arr[5];

(b) arr int[5];

(d) array arr(5);

► (a) int arr[5];

11. Which statement about functions in C is true?

(a) They cannot return values

(b) They must always be void

(d) They cannot take parameters

► (c) They can return any single value type

12. Which operator increments a variable by 1?

(a) +

(b) ++

(d) inc

► (b) ++

13. Which of these is a valid comment in C?

(a) # comment

(b) // comment

(d)

► (b) // comment

14. Which keyword is used to exit from a loop immediately?

(a) exit

(b) stop

(d) quit

► (c) break

15. Which function is used to find the length of a string in C?

(a) length()

(b) strlen()

(d) strlength()

► (b) strlen()

16. What is the index of the first element in a C array?

(a) 1

(b) 0

(d) Depends on compiler

► (b) 0

17. Which operator is used to access the value stored at a memory address?

(a) &

(b) *

(d) %

► (b) *

18. In the subtraction calculator, which variables represent the numbers?

(a) alpha, beta

(b) minuend, subtrahend

(d) num1, num2

► (b) minuend, subtrahend