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Basic C Programs

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Sample C Programs with explanation

C Programming Basics

About Lesson

Program 1: Hello, World!

#include <stdio.h>

int main() {
printf(“Hello, World!n”);
return 0;
}

Explanation:

#include <stdio.h>: This line includes the standard input/output library for using functions like printf and scanf.
int main(): This is the main function where the program execution starts.
printf("Hello, World!n");: This line prints the message “Hello, World!” to the screen.
return 0;: This line indicates that the program has executed successfully.

Program 2: Simple Addition

#include <stdio.h>

int main() {
int num1, num2, sum;

num1 = 5;
num2 = 7;
sum = num1 + num2;

printf(“Sum: %dn”, sum);

return 0;
}

Explanation:

int num1, num2, sum;: Declare integer variables num1, num2, and sum.
num1 = 5; and num2 = 7;: Assign values to num1 and num2.
sum = num1 + num2;: Calculate the sum of num1 and num2.
printf("Sum: %dn", sum);: Print the result, which is the sum of num1 and num2.

Program 3: Simple If-Else

#include <stdio.h>

int main() {
int num;

printf(“Enter a number: “);
scanf(“%d”, &num);

if (num > 0) {
printf(“Positive numbern”);
} else if (num < 0) {
printf(“Negative numbern”);
} else {
printf(“Zeron”);
}

return 0;
}

Explanation:

int num;: Declare an integer variable num.
printf("Enter a number: ");: Prompt the user to enter a number.
scanf("%d", &num);: Read the user’s input and store it in the variable num.
The if-else block checks if num is positive, negative, or zero, and prints the corresponding message.

Program 4: Finding the Maximum of Two Numbers

#include <stdio.h>

int main() {
int num1, num2;

printf(“Enter two numbers: “);
scanf(“%d %d”, &num1, &num2);

if (num1 > num2) {
printf(“Maximum: %dn”, num1);
} else {
printf(“Maximum: %dn”, num2);
}

return 0;
}

Explanation:

#include <stdio.h>: This line includes the standard input/output library for using functions like printf and scanf.
int num1, num2;: Declares two integer variables, num1 and num2.
printf("Enter two numbers: ");: Displays a message prompting the user to enter two numbers.
scanf("%d %d", &num1, &num2);: Reads two integer values entered by the user and stores them in num1 and num2.
The if-else block checks if num1 is greater than num2 and prints the maximum value accordingly.

Program 5: Factorial Calculation

#include <stdio.h>

int main() {
int n, i;
unsigned long long fact = 1;

printf(“Enter an integer: “);
scanf(“%d”, &n);

if (n < 0)
printf(“Factorial is not defined for negative numbers.n”);
else {
for (i = 1; i <= n; i++) {
fact *= i;
}
printf(“Factorial of %d = %llun”, n, fact);
}

return 0;
}

Explanation:

int n, i;: Declares integer variables n and i and an unsigned long long variable fact.
printf("Enter an integer: ");: Prompts the user to enter an integer.
scanf("%d", &n);: Reads the integer entered by the user and stores it in n.
The program calculates the factorial of n using a for loop.
The program handles negative input and displays an appropriate message.

Program 6: Simple For Loop

#include <stdio.h>

int main() {
int i;

for (i = 1; i <= 5; i++) {
printf(“%dn”, i);
}

return 0;
}

Explanation:

int i;: Declares an integer variable i.
The for loop runs from 1 to 5 and prints the value of i in each iteration.

Program 7: Sum of Natural Numbers

#include <stdio.h>

int main() {
int n, sum = 0;

printf(“Enter a positive integer: “);
scanf(“%d”, &n);

for (int i = 1; i <= n; i++) {
sum += i;
}

printf(“Sum of the first %d natural numbers = %dn”, n, sum);

return 0;
}

Explanation:

int n, sum = 0;: Declares integer variables n and sum.
printf("Enter a positive integer: ");: Prompts the user to enter a positive integer.
scanf("%d", &n);: Reads the integer entered by the user and stores it in n.
The for loop calculates the sum of the first n natural numbers.
The result is displayed as “Sum of the first n natural numbers = sum.”

Program 8: Check for Even or Odd

#include <stdio.h>

int main() {
int num;

printf(“Enter an integer: “);
scanf(“%d”, &num);

if (num % 2 == 0) {
printf(“%d is even.n”, num);
} else {
printf(“%d is odd.n”, num);
}

return 0;
}

Explanation:

This program checks if a given integer is even or odd and prints the result.
if (num % 2 == 0): Checks if the remainder of num divided by 2 is equal to 0, which is the condition for an even number.
printf("%d is even.n", num);: Prints that the number is even if the condition is true, otherwise, it prints that the number is odd.

Program 9: Calculate the Average of N Numbers

#include <stdio.h>

int main() {
int n, i;
float sum = 0, num;

printf(“Enter the number of elements: “);
scanf(“%d”, &n);

printf(“Enter %d numbers:n”, n);
for (i = 0; i < n; i++) {
scanf(“%f”, &num);
sum += num;
}

float average = sum / n;
printf(“Average = %.2fn”, average);

return 0;
}

Explanation:

This program calculates the average of a set of numbers entered by the user.
int n, i; and float sum = 0, num;: Declare integer variables n and i and float variables sum and num.
The program reads the number of elements and the numbers from the user and calculates their sum.
The average is calculated and displayed with two decimal places using %.2f.

Program 10: Display Multiplication Table

#include <stdio.h>

int main() {
int num, i;

printf(“Enter an integer: “);
scanf(“%d”, &num);

printf(“Multiplication Table for %d:n”, num);
for (i = 1; i <= 10; i++) {
printf(“%d x %d = %dn”, num, i, num * i);
}

return 0;
}

Explanation:

This program displays the multiplication table for a given integer.
printf("Multiplication Table for %d:n", num);: Prints the title for the multiplication table.
The program uses a for loop to calculate and display the results for the multiplication table from 1 to 10.

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