#include <stdio.h>
#include <string.h>
#include <malloc.h>
 
int main()
{
   char first[100], second[100], *temp;
 
   printf("Enter the first string\n");
   gets(first);
 
   printf("Enter the second string\n");
   gets(second);
 
   printf("\nBefore Swapping\n");
   printf("First string: %s\n",first);
   printf("Second string: %s\n\n",second);
 
   temp = (char*)malloc(100);
 
   strcpy(temp,first);
   strcpy(first,second);
   strcpy(second,temp);
 
   printf("After Swapping\n");
   printf("First string: %s\n",first);
   printf("Second string: %s\n",second);
 
   return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
int main()
{
   char ch, input[100], output[100];
   int no[26] = {0}, n, c, t, x;
 
   printf("Enter some text\n");
   scanf("%s", input);
 
   n = strlen(input);
 
   /** Store how many times characters (a to z) 
      appears in input string in array */
 
   for (c = 0; c < n; c++)
   {
      ch = input[c] - 'a';
      no[ch]++;
   }
 
   t = 0;
 
   /** Insert characters a to z in output string 
       that many number of times as they appear 
       in input string */
 
   for (ch = 'a'; ch <= 'z'; ch++)
   {
      x = ch - 'a';
 
      for (c = 0; c < no[x]; c++)
      {
         output[t] = ch;
         t++;
      }
   }
   output[t] = '\0';
 
   printf("%s\n", output);
 
   return 0;
}

#include <stdio.h>
 
int main() 
{
   char string[1000], sub[1000];
   int position, length, c = 0;
 
   printf("Input a string\n");
   gets(string);
 
   printf("Enter the position and length of substring\n");
   scanf("%d%d", &position, &length);
 
   while (c < length) {
      sub[c] = string[position+c-1];
      c++;
   }
   sub[c] = '\0';
 
   printf("Required substring is \"%s\"\n", sub);
 
   return 0;
}

// C program to convert string to integer without using atoi function
#include <stdio.h>
 
int toString(char []);
 
int main()
{
  char a[100];
  int n;
 
  printf("Input a valid string to convert to integer\n");
  scanf("%s", a);
 
  n = toString(a);
 
  printf("String  = %s\nInteger = %d\n", a, n);
 
  return 0;
}
 
int toString(char a[]) {
  int c, sign, offset, n;
 
  if (a[0] == '-') {  // Handle negative integers
    sign = -1;
  }
 
  if (sign == -1) {  // Set starting position to convert
    offset = 1;
  }
  else {
    offset = 0;
  }
 
  n = 0;
 
  for (c = offset; a[c] != '\0'; c++) {
    n = n * 10 + a[c] - '0';
  }
 
  if (sign == -1) {
    n = -n;
  }
 
  return n;
}

#include <stdio.h>
#include <string.h>
 
int main()
{
   char a[100], b[100];
 
   printf("Enter the string to check if it is a palindrome\n");
   gets(a);
 
   strcpy(b,a);
   strrev(b);
 
   if (strcmp(a,b) == 0)
      printf("Entered string is a palindrome.\n");
   else
      printf("Entered string is not a palindrome.\n");
 
   return 0;
}

#include <stdio.h>
#include <string.h>
 
int main()
{
   char arr[100];
 
   printf("Enter a string to reverse\n");
   gets(arr);
 
   strrev(arr);
 
   printf("Reverse of entered string is \n%s\n",arr);
 
   return 0;
}

#include <stdio.h>
#include <string.h>
 
int main()
{
   char a[1000], b[1000];
 
   printf("Enter the first string\n");
   gets(a);
 
   printf("Enter the second string\n");
   gets(b);
 
   strcat(a,b);
 
   printf("String obtained on concatenation is %s\n",a);
 
   return 0;
}

#include <stdio.h>
#include <string.h>
 
int main()
{
   char a[100], b[100];
 
   printf("Enter the first string\n");
   gets(a);
 
   printf("Enter the second string\n");
   gets(b);
 
   if (strcmp(a,b) == 0)
      printf("Entered strings are equal.\n");
   else
      printf("Entered strings are not equal.\n");
 
   return 0;
}

#include <stdio.h>
#include <string.h>
 
int main()
{
   char a[100];
   int length;
 
   printf("Enter a string to calculate it's length\n");
   gets(a);
 
   length = strlen(a);
 
   printf("Length of entered string is = %d\n",length);
 
   return 0;
}

#include <stdio.h>
 
int main()
{
  int m, n, p, q, c, d, k, sum = 0;
  int first[10][10], second[10][10], multiply[10][10];
 
  printf("Enter the number of rows and columns of first matrix\n");
  scanf("%d%d", &m, &n);
  printf("Enter the elements of first matrix\n");
 
  for (c = 0; c < m; c++)
    for (d = 0; d < n; d++)
      scanf("%d", &first[c][d]);
 
  printf("Enter the number of rows and columns of second matrix\n");
  scanf("%d%d", &p, &q);
 
  if (n != p)
    printf("Matrices with entered orders can't be multiplied with each other.\n");
  else
  {
    printf("Enter the elements of second matrix\n");
 
    for (c = 0; c < p; c++)
      for (d = 0; d < q; d++)
        scanf("%d", &second[c][d]);
 
    for (c = 0; c < m; c++) {
      for (d = 0; d < q; d++) {
        for (k = 0; k < p; k++) {
          sum = sum + first[c][k]*second[k][d];
        }
 
        multiply[c][d] = sum;
        sum = 0;
      }
    }
 
    printf("Product of entered matrices:-\n");
 
    for (c = 0; c < m; c++) {
      for (d = 0; d < q; d++)
        printf("%d\t", multiply[c][d]);
 
      printf("\n");
    }
  }
 
  return 0;
}

#include <stdio.h>
 
int main()
{
   int m, n, c, d, matrix[10][10], transpose[10][10];
 
   printf("Enter the number of rows and columns of matrix\n");
   scanf("%d%d", &m, &n);
 
   printf("Enter the elements of matrix\n");
 
   for (c = 0; c < m; c++)
      for(d = 0; d < n; d++)
         scanf("%d",&matrix[c][d]);
 
   for (c = 0; c < m; c++)
      for( d = 0 ; d < n ; d++ )
         transpose[d][c] = matrix[c][d];
 
   printf("Transpose of entered matrix :-\n");
 
   for (c = 0; c < n; c++) {
      for (d = 0; d < m; d++)
         printf("%d\t",transpose[c][d]);
      printf("\n");
   }
 
   return 0;
}