16(a). Another way to swap two numbers.
#include <stdio.h>

int main() {
int a,b;
printf("Enter two number for swapping: ");
scanf("%d %d",&a,&b);
printf("a = %d\nb= %d\n",a,b);
a = a*b;
b = a/b;
a = a/b;
printf("a=%d\nb=%d",a,b);
return 0;
}

19. C program to print ABCD and abcd.
#include <stdio.h>

int main() {
char i,j;
printf("small letters\n");
for(i='a';i<='z';i++){
printf ("%c ",i);
}
printf("\n\nCAPITAL LATTERS\n");
for(j='A';j<='Z';j++){
printf ("%c ",j);
}

return 0;
}

20. C program to find multiplication of two matrices.
#include <stdio.h>

int main()
{
printf ("***matrices multiplication***\n");
int a[2][2], b[2][2], c[2][2];
int i, j;
printf("enterthe elements of 1st matric:\n");
for(i = 0;i< 2;i++){
for(j = 0;j< 2;j++)
scanf("%d",&a[i][j]);
}

printf("enter the elements of 2nd matric:\n");
for(i = 0;i< 2;i++){
for(j = 0;j< 2;j++)
scanf("%d",&b[i][j]);
}

printf ("resulted matric..\n");
for(i = 0;i< 2;i++){
for(j = 0;j< 2;j++){
c[i][j]=0;
for(int k=0; k<2; k++){
c[i][j] += a[i][k] * b[k][j];
}
printf ("%d ",c[i][j]);
}
printf ("\n");
}
return 0;

}
i

21. C program to swap two characters.
#include <stdio.h>

void character_swaping(char *a, char *b);

int main()
{
char ch1 = 's';
char ch2 = 'r';
printf("character before swaping:\nch1 = %c ch2 = %c\n",ch1, ch2);
character_swaping(&ch1, &ch2);
printf("character after swaping:\nch1 = %c ch2 = %c\n",ch1, ch2);
return 0;
}
void character_swaping(char *a, char *b){
char temp;
temp = *a;
*a = *b;
*b = temp;
}

22. C program to print numbers from 1 to 10 without using loop.
#include <stdio.h>

int res(int num){
static int s = 1;
if (s == num+1)
return 1;
printf ("%d ", s);
s++;
res(num);
}
int main() {
int p = 10;
res(p);
return 0;
}

23. C program to convert numbers into roman digit's.
#include<stdio.h>

int rom(int, char);
int roman(int n){
int m = n/1000;
n = n % 1000;
rom(m,'m');

int d = n /500;
n = n % 500;
rom(d,'D');

int c = n /100;
n = n % 100;
rom(c,'c');

int l = n /50;
n = n % 50;
rom(l,'L');


int x = n /10;
n = n % 10;
rom(x,'x');

int v = n /5;
n = n % 5;
rom(v,'v');

int i = n /1;
n = n % 1;
rom(i,'i');
return 0;
}

int rom(int q,char h){
for(int i =0;i<q;i++){
printf ("%c",h);
}
return 0;

}

int main() {

int num;
scanf("%d",&num);
printf("Roman value of %d is: ", num);
roman(num);
return 0;
}

If you've any query or doubt about these programs , kindly DM me , I'll try to solve them.
Thank you..
Happy Coding :)

24. C program to print all leap years in between 1 and 5000 using control statements.
#include <stdio.h>

int main()
{
for(int year = 1; year <= 5000; year++){
if(year % 4==0){
printf("year %d is a leap year\n", year);
}
}
return 0;
}

25. C program to add two matrices.
#include <stdio.h>

int main()
{
printf ("***matrices addition***\n");
int a[2][2], b[2][2], c[2][2];
int i, j;
printf("enter the elements of 1st matric:\n");
for(i = 0;i< 2;i++){
for(j = 0;j< 2;j++)
scanf("%d",&a[i][j]);
}

printf("enter the elements of 2nd matric:\n");
for(i = 0;i< 2;i++){
for(j = 0;j< 2;j++)
scanf("%d",&b[i][j]);
}

printf ("resulted matric..\n");
for(i = 0;i< 2;i++){
for(j = 0;j< 2;j++){
c[i][j] = a[i][j] + b[i][j];

printf ("%d",c[i][j]);
}
printf ("\n");
}
return 0;
}

26. C program to find individual digits without using if-else and switch case instructions.
#include <stdio.h>

char ind[][10] = {"zero","one","two","three","four","five", "six", "seven", "eight","nine"};
void find(int num){
int dg[10], count=0;
do{
dg[count] = num % 10;
num /= 10;
count++;
} while (num != 0);
for(int i = count -1; i >= 0; i--){
printf("%s ", ind[dg[i]]);
}
}

int main(){
int num;
printf ("enter a number: ");
scanf ("%d",&num);
find(num);
return 0;
}

27. C program to find sum of individual number.
#include<stdio.h>
int main(){
int num, sum;
scanf("%d",&num);
while(num>0){
sum += num % 10;
num /= 10;
}
printf("sum of individual digits is %d", sum);
return 0;
}\

28. C program to find whether a character is a vowel or not.
#include <stdio.h>

int main(){
char ch;
printf("Enter a character: ");
scanf("%c",&ch);
if(ch==97 ch==101 ch==105 ch==111 ch==117)
{
printf("%c is vowel!",ch);
}
else
{
printf("%c is a constant!",ch);
}
return 0;
}

#Explanation:
The correct answer is 3rd becoz , as you all know that '//' are used for give a comment, comment means compiler will skip these part of the code, and will execute next statement of the code, but if I write a comment , which will terminate with '\' symbol then compiler will skip the next line of the code and will execute the third line of the code and that's known as "Line splicing".
Hope you understood!
Happy coding :)

29. C program to find whether a character is a upper case character or lower case character or special symbol or a number(by using switch case instructions).
#include <stdio.h>

int main(){
char ch;
int val =0;
printf("enter a character: ");
scanf("%c",&ch);
if(ch>= 97 && ch<= 122)
val = 1;
else if(ch>=65 && ch<90)
val = 2;
else if(ch>=33 && ch<= 64 || ch>=91 && ch<=96)
val = 3;
else if(ch >= 48 && ch<=57)
val = 4;
else
val = 0;
switch(val){
case 1:
printf("%c is a lower case alphabet",ch);
break;
case 2:
printf("%c is a upper case alphabet",ch);
break;
case 3:
printf("%c is a special symbol",ch);
break;
case 4:
printf("%c is a numerical digit",ch);
default:
printf("Another character");
}
return 0;
}

Bot for executing snippets of code; /help to get more information, /languages for list of languages. https://t.me/rextester_bot

This bot will help you to run your code on telegram

But it can not take any input from keyboard.