C Program to check if input Number is int or float

#include<stdio.h>

#include<conio.h>
#include<string.h>

int main()
{
   char number[10];
    int flag = 0;
    int length, i = 0;

    printf("\n\nEnter a number: ");
    scanf("%s", number);

    length = strlen(number);

    // till string does not end
    while(number[i++] != '\0')    // same as while(length-->0)
    {
        if(number[i] == '.')    // decimal point is present
        {
            flag = 1;
            break;
        }
    }

    // if(0) is same as if(false)
    if(flag)
        printf("\n\n\n\tEntered Number is a Floating point Number\n\n");
    else
        printf("\n\n\n\tEntered Number is a integer Number\n\n");
    return 0;
}

Null Pointer Program

#include<stdio.h>

int main()
{
    int *ptr = NULL;    // ptr is a NULL pointer
    printf("\n\n The value of ptr is: %x ", ptr);
      return 0;
}

Output: The value of ptr is: 0

C Program to check whether a two dimensional array is a Sparse Matrix

#include<stdio.h>

int main()
{
    int n, m, c, d, matrix[10][10];
    int counter = 0;
    printf("\nEnter the number of rows and columns of the matrix \n\n");
    scanf("%d%d",&m,&n);

    printf("\nEnter the %d elements of the matrix \n\n", m*n);
    for(c = 0; c < m; c++)   // to iterate the rows
    {
        for(d = 0; d < n; d++)   // to iterate the columns
        {
            scanf("%d", &matrix[c][d]);
            if(matrix[c][d] == 0)
            counter++;  // same as counter=counter +1
        }
    }

    // printing the matrix
    printf("\n\nThe entered matrix is: \n\n");
    for(c = 0; c < m; c++)   // to iterate the rows
    {
        for(d = 0; d < n; d++)   // to iterate the columns
        {
            printf("%d\t", matrix[c][d]);
        }
    printf("\n"); // to take the control to the next row
    }

    // checking if the matrix is sparse or not
    if(counter > (m*n)/2)
        printf("\n\nThe entered matrix is a sparse matrix\n\n");
    else
        printf("\n\nThe entered matrix is not a sparse matrix\n\n");

    return 0;
}

Dynamic Memory Allocation using malloc()

#include <stdio.h>

int main()
{
    int n, i, *ptr, sum = 0;

    printf("\n\nEnter number of elements: ");
    scanf("%d", &n);

    // dynamic memory allocation using malloc()
    ptr = (int *) malloc(n*sizeof(int));

    if(ptr == NULL) // if empty array
    {
        printf("\n\nError! Memory not allocated\n");
        return 0;   // end of program
    }

    printf("\n\nEnter elements of array: \n\n");
    for(i = 0; i < n; i++)
    {
        // storing elements at contiguous memory locations
        scanf("%d", ptr+i);   
        sum = sum + *(ptr + i);
    }

    // printing the array elements using pointer to the location
    printf("\n\nThe elements of the array are: ");
    for(i = 0; i < n; i++)
    {
        printf("%d  ",ptr[i]);    // ptr[i] is same as *(ptr + i)
    }

    /*
        freeing memory of ptr allocated by malloc
        using the free() method
    */
    free(ptr);
    return 0;
}

find the Size of any File

#include<stdio.h>
#include<conio.h>

void main()
{
    FILE *fp;
    char ch;
    int size = 0;

    fp = fopen("program.txt", "r");
    if (fp == NULL)
    {
        printf("\nFile unable to open...");
    }
    else
    {
        printf("\nFile opened...");
    }
    fseek(fp, 0, 2);    /* File pointer at the end of file */
    size = ftell(fp);   /* Take a position of file pointer in size variable */
    printf("The size of given file is: %d\n", size);
    fclose(fp);
}

Print names of all Files present in a Directory

#include<stdio.h>
#include<dirent.h>

int main(void)
{
    DIR *d;
    struct dirent *dir;
    d = opendir(".");
    if (d)
    {
        while ((dir = readdir(d)) != NULL)
        {
            printf("%s\n", dir->d_name);
        }
        closedir(d);
    }
    return(0);
}

Program to convert Temparature in Celsius to Fahrenheit

#include<stdio.h>

int main()
{
        float celsius, fahrenheit;
    printf("\n\nEnter temperature in Celsius: ");
    scanf("%f", &celsius);
   
    fahrenheit = (1.8*celsius) + 32;
    printf("\n\n\nTemperature in Fahrenheit is: %f ", fahrenheit);

    return 0;
}

C Program to Calculate Permutation (nPr) and Combination (nCr)

#include<stdio.h>

// function prototype declarations
long factorial(int);
long find_npr(int, int);
long find_ncr(int, int);

int main()
{
     int n, r;
    long npr, ncr;

    printf("Enter the value of n and r respectively: \n\n");
    scanf("%d%d", &n, &r);

    // function calls
    npr = find_npr(n, r);
    ncr = find_ncr(n, r);

    printf("\n\n\n\t\t%dC%d = %ld\n", n, r, ncr);
    printf("\n\n\t\t%dP%d = %ld\n", n, r, npr);

    printf("\n\n\t\t\tCoding is Fun !\n\n\n");
    return 0;
}

/*
    function definition for nCr
*/
long find_ncr(int a, int b)
{
    return (factorial(a)/(factorial(b)*factorial(a-b)));
}

/*
    function definition for nPr
*/
long find_npr(int a, int b)
{
    return (factorial(a)/factorial(a-b));
}

/*
    recursive function definition for finding
    factorial of a number
*/
long factorial(int c)
{
    if(c == 1 || c == 0)
        return 1;
    else
        return c*factorial(c-1);
}

C Program to Display the current Date and Time

#include<stdio.h>
#include<time.h>

void main()
{
  time_t t;   // not a primitive datatype
    time(&t);
clrscr();
    printf("\n\n\t\tStudytonight - Best place to learn\n\n\n");

    printf("\nThis program has been writeen at (date and time): %s", ctime(&t));

    printf("\n\n\t\t\tCoding is Fun !\n\n\n");
getch();
}

C Program to remove Duplicate Element in an Array

#include<stdio.h>
#include<conio.h>
void main()
{
    int a[20], i, j, k, n;
    clrscr();

    printf("\nEnter array size: ");
    scanf("%d", &n);

    printf("\nEnter %d array element: ", n);
    for(i = 0; i < n; i++)
    {
        scanf("%d", &a[i]);
    }

    printf("\nOriginal array is: ");
    for(i = 0; i < n; i++)
    {
        printf(" %d", a[i]);
    }

    printf("\nNew array is: ");
    for(i = 0; i < n; i++)
    {
        for(j = i+1; j < n; )
        {
            if(a[j] == a[i])
            {
                for(k = j; k < n; k++)
                {
                    a[k] = a[k+1];
                }
                n--;
            }
            else
            {
                j++;
            }
        }
    }

    for(i = 0; i < n; i++)
    {
        printf("%d ", a[i]);
    }
    getch();
}

OUTPUT:-