1.      Program to print full pyramid using *

       *
      * * *
    * * * * *
  * * * * * * *
* * * * * * * * *
Solution:
#include <stdio.h>
int main()
{
    int i, space, rows, k=0;

    printf("Enter number of rows: ");
    scanf("%d",&rows);

    for(i=1; i<=rows; ++i, k=0)
    {
        for(space=1; space<=rows-i; ++space)
        {
            printf("  ");
        }

        while(k != 2*i-1)
        {
            printf("* ");
            ++k;
        }

        printf("\n");
    }
   
    return 0;
}

2. Program to Check Prime Number
#include <stdio.h>
int main()
{
    int n, i, flag = 0;

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

    for(i = 2; i <= n/2; ++i)
    {
        // condition for nonprime number
        if(n%i == 0)
        {
            flag = 1;
            break;
        }
    }

    if (n == 1)
    {
      printf("1 is neither a prime nor a composite number.");
    }
    else
    {
        if (flag == 0)
          printf("%d is a prime number.", n);
        else
          printf("%d is not a prime number.", n);
    }
   
    return 0;
}
Output
Enter a positive integer: 29
29 is a prime number.

3. Program to Count Number of Digits in an Integer
#include <stdio.h>
int main()
{
    long long n;
    int count = 0;

    printf("Enter an integer: ");
    scanf("%lld", &n);

    while(n != 0)
    {
        // n = n/10
        n /= 10;
        ++count;
    }

    printf("Number of digits: %d", count);
}
Output
Enter an integer: 3452
Number of digits: 4



4. Program to Check Vowel or consonant
#include <stdio.h>
int main()
{
    char c;
    int isLowercaseVowel, isUppercaseVowel;

    printf("Enter an alphabet: ");
    scanf("%c",&c);

    // evaluates to 1 (true) if c is a lowercase vowel
    isLowercaseVowel = (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u');

    // evaluates to 1 (true) if c is an uppercase vowel
    isUppercaseVowel = (c == 'A' || c == 'E' || c == 'I' || c == 'O' || c == 'U');

    // evaluates to 1 (true) if either isLowercaseVowel or isUppercaseVowel is true
    if (isLowercaseVowel || isUppercaseVowel)
        printf("%c is a vowel.", c);
    else
        printf("%c is a consonant.", c);
    return 0;
}
Output
Enter an alphabet: G
G is a consonant.
5. Program to Print ASCII Value
#include <stdio.h>
int main()
{
    char c;
    printf("Enter a character: ");

    // Reads character input from the user
    scanf("%c", &c); 
   
    // %d displays the integer value of a character
    // %c displays the actual character
    printf("ASCII value of %c = %d", c, c);
    return 0;
}
Output
Enter a character: G
ASCII value of G = 71
6. Program to Swap Numbers Using Temporary Variable
#include <stdio.h>
int main()
{
      double firstNumber, secondNumber, temporaryVariable;

      printf("Enter first number: ");
      scanf("%lf", &firstNumber);

      printf("Enter second number: ");
      scanf("%lf",&secondNumber);

      // Value of firstNumber is assigned to temporaryVariable
      temporaryVariable = firstNumber;

      // Value of secondNumber is assigned to firstNumber
      firstNumber = secondNumber;

      // Value of temporaryVariable (which contains the initial value of firstNumber) is assigned to secondNumber
      secondNumber = temporaryVariable;

      printf("\nAfter swapping, firstNumber = %.2lf\n", firstNumber);
      printf("After swapping, secondNumber = %.2lf", secondNumber);

      return 0;
}


Output
Enter first number: 1.20
Enter second number: 2.45

After swapping, firstNumber = 2.45
After swapping, secondNumber = 1.20
7.Fibonacci Series up to n number of terms
#include <stdio.h>
int main()
{
    int i, n, t1 = 0, t2 = 1, nextTerm;

    printf("Enter the number of terms: ");
    scanf("%d", &n);

    printf("Fibonacci Series: ");

    for (i = 1; i <= n; ++i)
    {
        printf("%d, ", t1);
        nextTerm = t1 + t2;
        t1 = t2;
        t2 = nextTerm;
    }
    return 0;
}
Enter the number of terms: 10
Fibonacci Series: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34,
8. GCD Using while loop and if...else Statement
#include <stdio.h>
int main()
{
    int n1, n2;
   
    printf("Enter two positive integers: ");
    scanf("%d %d",&n1,&n2);

    while(n1!=n2)
    {
        if(n1 > n2)
            n1 -= n2;
        else
            n2 -= n1;
    }
    printf("GCD = %d",n1);

    return 0;
}
Output
Enter two positive integers: 81
153
GCD = 9
9.LCM using while Loop and if Statement

#include <stdio.h>
int main()
{
    int n1, n2, minMultiple;
    printf("Enter two positive integers: ");
    scanf("%d %d", &n1, &n2);

    // maximum number between n1 and n2 is stored in minMultiple
    minMultiple = (n1>n2) ? n1 : n2;

    // Always true
    while(1)
    {
        if( minMultiple%n1==0 && minMultiple%n2==0 )
        {
            printf("The LCM of %d and %d is %d.", n1, n2,minMultiple);
            break;
        }
        ++minMultiple;
    }
    return 0;
}
Output
Enter two positive integers: 72
120
The LCM of 72 and 120 is 360.

10. Program to Add Two Matrices
#include <stdio.h>
int main(){
    int r, c, a[100][100], b[100][100], sum[100][100], i, j;

    printf("Enter number of rows (between 1 and 100): ");
    scanf("%d", &r);
    printf("Enter number of columns (between 1 and 100): ");
    scanf("%d", &c);

    printf("\nEnter elements of 1st matrix:\n");

    for(i=0; i<r; ++i)
        for(j=0; j<c; ++j)
        {
            printf("Enter element a%d%d: ",i+1,j+1);
            scanf("%d",&a[i][j]);
        }

    printf("Enter elements of 2nd matrix:\n");
    for(i=0; i<r; ++i)
        for(j=0; j<c; ++j)
        {
            printf("Enter element a%d%d: ",i+1, j+1);
            scanf("%d", &b[i][j]);
        }

    // Adding Two matrices

    for(i=0;i<r;++i)
        for(j=0;j<c;++j)
        {
            sum[i][j]=a[i][j]+b[i][j];
        }

    // Displaying the result
    printf("\nSum of two matrix is: \n\n");

    for(i=0;i<r;++i)
        for(j=0;j<c;++j)
        {

            printf("%d   ",sum[i][j]);

            if(j==c-1)
            {
                printf("\n\n");
            }
        }
   
    return 0;
}
Output
Enter number of rows (between 1 and 100): 2
Enter number of columns (between 1 and 100): 3

Enter elements of 1st matrix:
Enter element a11: 2
Enter element a12: 3
Enter element a13: 4
Enter element a21: 5
Enter element a22: 2
Enter element a23: 3
Enter elements of 2nd matrix:
Enter element a11: -4
Enter element a12: 5
Enter element a13: 3
Enter element a21: 5
Enter element a22: 6
Enter element a23: 3

Sum of two matrix is:

-2   8   7  

10   8   6
11. Write to a text file using fprintf()
#include <stdio.h>
#include <stdlib.h>

int main()
{
   int num;
   FILE *fptr;
   fptr = fopen("C:\\program.txt","w");

   if(fptr == NULL)
   {
      printf("Error!");  
      exit(1);            
   }

   printf("Enter num: ");
   scanf("%d",&num);

   fprintf(fptr,"%d",num);
   fclose(fptr);

   return 0;
}

12. Read from a text file using fscanf()
#include <stdio.h>
#include <stdlib.h>

int main()
{
   int num;
   FILE *fptr;

   if ((fptr = fopen("C:\\program.txt","r")) == NULL){
       printf("Error! opening file");

       // Program exits if the file pointer returns NULL.
       exit(1);
   }

   fscanf(fptr,"%d", &num);

   printf("Value of n=%d", num);
   fclose(fptr);
 
   return 0;
}

13. Accessing Two-Dimensional Array Elements
#include <stdio.h>

int main () {

   /* an array with 5 rows and 2 columns*/
   int a[5][2] = { {0,0}, {1,2}, {2,4}, {3,6},{4,8}};
   int i, j;

   /* output each array element's value */
   for ( i = 0; i < 5; i++ ) {

      for ( j = 0; j < 2; j++ ) {
         printf("a[%d][%d] = %d\n", i,j, a[i][j] );
      }
   }
  
   return 0;
}

When the above code is compiled and executed, it produces the following result −
a[0][0]: 0
a[0][1]: 0
a[1][0]: 1
a[1][1]: 2
a[2][0]: 2
a[2][1]: 4
a[3][0]: 3
a[3][1]: 6
a[4][0]: 4
a[4][1]: 8

14. max() along with main() and compiled the source code.


#include <stdio.h>

/* function declaration */
int max(int num1, int num2);

int main () {

   /* local variable definition */
   int a = 100;
   int b = 200;
   int ret;

   /* calling a function to get max value */
   ret = max(a, b);

   printf( "Max value is : %d\n", ret );

   return 0;
}

/* function returning the max between two numbers */
int max(int num1, int num2) {

   /* local variable declaration */
   int result;

   if (num1 > num2)
      result = num1;
   else
      result = num2;

   return result;
}


We have kept max() along with main() and compiled the source code. While running the final executable, it would produce the following result −

Max value is : 200