Skip to content

C Programming Foundations

Introduction

Welcome to the world of C programming! In this guide, we'll cover essential concepts and problem-solving techniques that will set the foundation for your journey into the programming realm.

Table of Contents

  1. Variables
  2. What are Variables?
  3. Using Variables
  4. Loops
  5. What are Loops?
  6. For Loop
  7. Problem: Factorial Calculation
  8. While Loop
  9. Problem: Print N numbers
  10. Do-While Loop
  11. Problem: Add numbers entered by user
  12. Switch...Case
  13. Problem: Simple Calculator
  14. Conditional Statements
  15. What are Conditional Statements?
  16. if-else statement
  17. Problem: Leap Year Checker
  18. if-else ladder
  19. Nested if-else
  20. Arrays
  21. What are Arrays?
  22. Past Year Questions

Variables in C

What are Variables?

In programming, variables are containers that store data. They have a type and a name.

int age;  // Declaration
age = 21; // Assignment
Note: The value of a variable can be changed, hence the name variable.

char ch = 'a';
ch = 'l';

C is a strongly typed language. This means that the variable type cannot be changed once it is declared. For example:

int number = 5;     // integer variable
number = 5.5;       // error, can't assign float to int
double number;      // error, can't redefine the data type

Using variables

Once a variable has been declared and initialized, you can use it in your program to store and retrieve data. For example, the following code prints the value of the variable age to the console:

#include <stdio.h>

int main() {
  int age = 25;

  printf("My age is %d\n", age);

  return 0;
}

Loops in C

What are Loops?

In programming, a loop is used to repeat a block of code until the specified condition is met.

For Loop

for (int i = 0; i < 5; i++) {
    // Code inside the loop
}
For Loop Working
Working of For Loop

Problem: Factorial Calculation

Write a program to find the factorial of a number. 

#include <stdio.h>

int main() {                        // return type int
    int number, factorial = 1;

    printf("Enter a number: ");   //Prints text to console
    scanf("%d", &number);         //Reads input from console

    for (int i = 1; i <= number; i++) {
        factorial *= i;
    }

    printf("Factorial: %d\n", factorial);

    return 0;
}

While loop

The syntax of the while loop is:

while (testExpression) {
  // the body of the loop 
}
While Loop Working
Working of While Loop

Problem: Print N numbers

#include <stdio.h>

void main() {                             //return type void
    int n, i;
    // Input the value of n
    printf("Enter the value of n: ");
    scanf("%d", &n);
    // Initialize a counter variable
    i = 1;

    // While loop to print the first n numbers
    while (i <= n) {
        printf("%d ", i);
        i++; // Increment the counter
    }
}

Do- While loop

The syntax of the do-while loop is:

do {
  // the body of the loop
}
while (testExpression);

Do While Loop Working
Working of do - while Loop

Problem: Add numbers entered by user

#include <stdio.h>
void main() {
  double number, sum = 0;

  // the body of the loop is executed at least once
  do {
    printf("Enter a number: ");
    scanf("%lf", &number);
    sum += number;
  }
  while(number != 0.0);
  printf("Sum = %.2lf",sum);
}

Switch...case loop

The syntax of the switch...case loop is:

switch (expression)
​{
    case constant1:
      // statements
      break;

    case constant2:
      // statements
      break;
    .
    .
    .
    default:
      // default statements
}

Switch case Working
Working of switch...case Loop

Problem: Simple Calculator

#include <stdio.h>

int main() {
    char operation;
    double n1, n2;

    printf("Enter an operator (+, -, *, /): ");
    scanf("%c", &operation);
    printf("Enter two operands: ");
    scanf("%lf %lf",&n1, &n2);    //lf reads type "double"

    switch(operation)
    {
        case '+':
            printf("%.1lf + %.1lf = %.1lf",n1, n2, n1+n2);
            break;

        case '-':
            printf("%.1lf - %.1lf = %.1lf",n1, n2, n1-n2);
            break;

        case '*':
            printf("%.1lf * %.1lf = %.1lf",n1, n2, n1*n2);
            break;

        case '/':
            printf("%.1lf / %.1lf = %.1lf",n1, n2, n1/n2);
            break;

        // operator doesn't match any case constant +, -, *, /
        default:
            printf("Error! operator is not correct");
    }
}

Conditional Statements in C

What are Conditional Statements?

Conditional statements help your program make decisions.

if-else statement

if (condition) {
    // Code to execute if the condition is true
} else {
    // Code to execute if the condition is false
}
If Else Working
Working of if-else Loop

Problem: Leap Year Checker

#include <stdio.h>

void main() {
    int year;
    printf("Enter a year: ");
    scanf("%d", &year);

    if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
        printf("Leap year\n");
    } else {
        printf("Not a leap year\n");
    }
}

if-else Ladder

Sometimes, a choice has to be made from more than 2 possibilities.

The if...else ladder allows you to check between multiple test expressions and execute different statements. 

if (test expression1) {
   // statement(s)
}
else if(test expression2) {
   // statement(s)
}
else if (test expression3) {
   // statement(s)
}
.
.
else {
   // statement(s)
}

Problem: if- else

// Program to relate two integers using =, > or < symbol

#include <stdio.h>
int main() {
    int number1, number2;
    printf("Enter two integers: ");
    scanf("%d %d", &number1, &number2);

    //checks if the two integers are equal.
    if(number1 == number2) {
        printf("Result: %d = %d",number1,number2);
    }

    //checks if number1 is greater than number2.
    else if (number1 > number2) {
        printf("Result: %d > %d", number1, number2);
    }

    //checks if both test expressions are false
    else {
        printf("Result: %d < %d",number1, number2);
    }
    return 0;
}

Nested if-else

#include <stdio.h>
int main() {
    int number1, number2;
    printf("Enter two integers: ");
    scanf("%d %d", &number1, &number2);

    if (number1 >= number2) {
      if (number1 == number2) {
        printf("Result: %d = %d",number1,number2);
      }
      else {
        printf("Result: %d > %d", number1, number2);
      }
    }
    else {
        printf("Result: %d < %d",number1, number2);
    }
    return 0;
}

Arrays in C

What are Arrays?

Arrays allow you to store multiple values of the same type under one name.

Syntax

dataType arrayName[arraySize];
//example
int numbers[5] = {1, 2, 3, 4, 5};`
If Else Working

Access Array Elements

You can access elements of an array by indices.

Suppose you declared an array mark as above. The first element is mark[0], the second element is mark[1] and so on.

C Array declaration

Past Year Questions 🤩🤩🤩

1) Write a C Program to input size of the array, and then replace each element of the user input array with its reverse. Print the array.

//Solution
#include <stdio.h>

void main() {
    int size;

    // Input the size of the array
    printf("Enter the size of the array: ");
    scanf("%d", &size);

    int arr[size];

    // Input array elements
    printf("Enter %d elements:\n", size);
    for (int i = 0; i < size; i++) {
        printf("Enter element %d :",i+1);
        scanf("%d", &arr[i]);
    }

    // Print the original array
    printf("Original Array: ");
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");

    // Reverse the array in-place
    int start = 0;
    int end = size - 1;
    while (start < end) {
        // Swap elements at start and end
        int temp = arr[start];
        arr[start] = arr[end];
        arr[end] = temp;

        // Move the start and end pointers
        start++;
        end--;
    }

    // Print the array after the reversal
    printf("Array After Reversal: ");
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

2) WAP to sort an array A[] consisting of only 1s, 2s, and 3s. the following task needs to be done

  • The program should sort the given array and put all 1s first, then all 2s and all 3s in last.
  • Print the array elements after sorting.


Test case 1:

Input: {1, 2, 3, 1, 2, 3}

Output: {1, 1, 2, 2, 3, 3}


Test case 2:

Input: {1, 2, 2, 1, 2, 3, 2, 3, 1, 1, 1, 2}

Output: {1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3}

//Solution
#include <stdio.h>

int main() {
    int size;

    // Input the size of the array
    printf("Enter the size of the array: ");
    scanf("%d", &size);

    int arr[size];

    // Input array elements
    printf("Enter %d elements (1, 2, or 3):\n", size);
    for (int i = 0; i < size; i++) {
        scanf("%d", &arr[i]);
    }

    int count1 = 0, count2 = 0, count3 = 0;

    // Count the occurrences of 1, 2, and 3 in the array
    for (int i = 0; i < size; i++) {
        if (arr[i] == 1) {
            count1++;
        } else if (arr[i] == 2) {
            count2++;
        } else if (arr[i] == 3) {
            count3++;
        }
    }

    // Overwrite the array with the sorted elements
    for (int i = 0; i < count1; i++) {
        arr[i] = 1;
    }

    for (int i = count1; i < count1 + count2; i++) {
        arr[i] = 2;
    }

    for (int i = count1 + count2; i < size; i++) {
        arr[i] = 3;
    }

    // Print the sorted array
    printf("Array After Sorting: ");
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");

    return 0;
}

Congratulations on completing this C programming foundations! Remember, practice is key to mastering programming. Explore more, solve problems, and enjoy the journey of coding! Happy coding! 😄

meme