Class-Discussion: C Programming Concepts
With Examples, Mini-Questions, and Hints
1. Header Files in C
What are header files?
Header files in C contain definitions of functions and macros that we can use in our
programs. Instead of writing common functions from scratch, we can #include header
files to use them.
Why do we include them?
- To reuse pre-defined functions. - To make the program modular and easy to read. - To
access libraries for math, input/output, memory, and time functions.
Common Header Files Used
• stdio.h: For standard input/output functions like printf(), scanf().
• stdlib.h: For memory allocation, random numbers, type conversions.
• time.h: To handle date and time, random seed initialization.
• math.h: For mathematical functions like sqrt(), pow(), sin(), etc.
// Example : Using header files
# include < stdio .h >
# include < stdlib .h >
# include < time .h >
# include < math .h >
int main () {
printf ( " Square root of 16 is : %.2 f \ n " , sqrt (16) ) ;
printf ( " Random number : % d \ n " , rand () ) ;
return 0;
}
Mini-Question 1: Write a program to generate a random number between 1 and
100. Hint: Use rand() with modulus and srand(time(0)) to change the sequence each
time.
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2. Declaring Variables in C
Types of variables
Variables are storage locations in memory.
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• int: Integer values (e.g., 5, -10).
• float: Decimal values (e.g., 3.14).
• double: Double precision floating point.
• char: Single character (e.g., ’A’).
// Example : Declaring variables
# include < stdio .h >
int main () {
int age = 25;
float pi = 3.14;
double g = 9.81;
char grade = ’A ’;
printf ( " Age = % d \ n " , age ) ;
printf ( " Pi = %.2 f \ n " , pi ) ;
printf ( " Gravity = %.2 lf \ n " , g ) ;
printf ( " Grade = % c \ n " , grade ) ;
return 0;
}
Mini-Question 2: Write a program to store your name’s first letter (char), age (int),
and height (float) and print them. Hint: Use %c, %d, %f in printf().
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3. Arrays in C
1-D Arrays
A 1-D array stores multiple values of the same type in a single variable.
# include < stdio .h >
int main () {
int marks [5] = {90 , 85 , 88 , 92 , 76};
for ( int i =0; i <5; i ++) {
printf ( " marks [% d ] = % d \ n " , i , marks [ i ]) ;
}
return 0;
}
2-D Arrays
A 2-D array is like a table with rows and columns.
# include < stdio .h >
int main () {
int matrix [2][3] = {{1 ,2 ,3} ,{4 ,5 ,6}};
for ( int i =0; i <2; i ++) {
for ( int j =0; j <3; j ++) {
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printf ( " % d " , matrix [ i ][ j ]) ;
}
printf ( " \ n " ) ;
}
return 0;
}
Mini-Question 3: Write a program to input 5 numbers into an array and print their
sum. Hint: Use a loop and a variable to keep adding.
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4. Decision Making in C: if-else
Simple if-else
# include < stdio .h >
int main () {
int num = 10;
if ( num % 2 == 0) {
printf ( " Even \ n " ) ;
} else {
printf ( " Odd \ n " ) ;
}
return 0;
}
if-else-if ladder
# include < stdio .h >
int main () {
int marks = 72;
if ( marks >= 90)
printf ( " Grade A \ n " ) ;
else if ( marks >= 75)
printf ( " Grade B \ n " ) ;
else if ( marks >= 50)
printf ( " Grade C \ n " ) ;
else
printf ( " Fail \ n " ) ;
return 0;
}
Mini-Question 4: Write a program to input a number and check if it is positive,
negative, or zero. Hint: Use if, else if, else.
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5. Looping in C
For Loop
Best used when the number of iterations is known.
# include < stdio .h >
int main () {
for ( int i =1; i <=5; i ++) {
printf ( " % d " , i ) ;
}
return 0;
}
While Loop
Best used when the number of iterations is not known beforehand.
# include < stdio .h >
int main () {
int i = 1;
while ( i <= 5) {
printf ( " % d " , i ) ;
i ++;
}
return 0;
}
Mini-Question 5: Write a program using a while loop to keep asking numbers
until the user enters 0. Print the sum of entered numbers. Hint: Use a variable to store
cumulative sum.
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6. User-Defined Functions in C
Example: Factorial Function
# include < stdio .h >
// User - defined function
int factorial ( int n ) {
int fact = 1;
for ( int i =1; i <= n ; i ++) {
fact *= i ;
}
return fact ;
}
int main () {
int num = 5;
printf ( " Factorial of % d = % d \ n " , num , factorial ( num ) ) ;
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return 0;
}
Example: Using Factorial to Compute nCx
# include < stdio .h >
// Factorial function
int factorial ( int n ) {
int fact = 1;
for ( int i =1; i <= n ; i ++) {
fact *= i ;
}
return fact ;
}
int main () {
int n = 5 , r = 2;
int nCr = factorial ( n ) / ( factorial ( r ) * factorial (n - r ) ) ;
printf ( " C (% d ,% d ) = % d \ n " , n , r , nCr ) ;
return 0;
}
Mini-Question 6: Write a function to compute the square of a number. Use it in
main() to compute a2 + b2 . Hint: Define a function returning int, call it twice.
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7. The main() Function in C
Every C program starts execution from the main() function. Inside main(), we can call
other functions, write loops, use arrays, and make decisions.
# include < stdio .h >
int add ( int a , int b ) {
return a + b ;
}
int main () {
int x = 5 , y = 7;
int sum = add (x , y ) ; // calling user - defined function
printf ( " Sum = % d \ n " , sum ) ;
return 0;
}
Mini-Question 7: Write a user-defined function to compute the cube of a number
and call it inside main().
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