Assignment on pointer with solution

Questions:
  1. Assume the definitions and initializations:
    char c = 'T', d = 'S';
char *p1 = &c;
char *p2 = &d;
char *p3;
				
    p3 = &d;
printf("*p3 = %s\n", *p3);   // (1)

p3 = p1;
printf("*p3 = %s , p3 = %u\n", *p3, p3);

*p1 = *p2;
printf("*p1 = %s , p1 = %u\n", *p1,p1);
    

    Ans.
    
	*p3 = S
	*p3 = T, p3 = 6940
	*p1 = S, p1 = 9772
  2. Consider the following statements: 
    int *p;
int i;
int k;
i = 42;
k = i;
p = &i;
				
    A. k = 75; 
B. *k = 75; 
C. p = 75; 
D. *p = 75; 
E. Two or more of the answers will change i to 75.
    

    Ans.
    
	D. *p = 75
  3. Explain the error. 
    char c = 'A';
double *p = &c;

    

    Ans.
    
	warning: initialization from incompatible pointer type
  4. Give the value of the left-hand side variable in each assignment statement. Assume the lines are executed sequentially. Assume the address of the blocks array is 4434. 
    int main()
{
   char blocks[3] = {'A','B','C'};
   char *ptr = &blocks[0]; // *ptr is initialized with 4434
   char temp;

   temp = blocks[0]; // temp = 'A'
   temp = *(blocks + 2); // temp = 'C'
   temp = *(ptr + 1); // temp = 'B'
   temp = *ptr; // temp = 'A'

   ptr = blocks + 1; // ptr = 4435
   temp = *ptr; // temp = 'B'
   temp = *(ptr + 1); // temp = 'C'

   ptr = blocks; // ptr = 4434
   temp = *++ptr; // temp = 'B'
   temp = ++*ptr; // temp = 'C'
   temp = *ptr++; // temp = 'C'
   temp = *ptr; // temp = 'C'

   return 0;
}
    5. For the following functions, use the pointer notation ONLY. Do NOT use the array index [] notation.
  5. Write a piece of code which prints the characters in a cstring in a reverse order. 
    char s[10] = "abcde";
char* cptr;

// WRITE YOUR CODE HERE

    Ans.
    
#include<stdio.h>
#include<string.h>
int main()
{
	char s[10] = "abcde";
	char* cptr;
	int i,l;
	l=strlen(s);
	cptr=s;
	cptr=cptr+l;
	for (i=l; i >= 0 ;i--)
	{
		printf("%c", *cptr);
		cptr--;
	}
	return 0;
}
  6. Write a function countEven(int*, int) which receives an integer array and its size, and returns the total number of even numbers in the array.
    	
    Ans. 
    
#include<stdio.h>
#include<stdlib.h>
int  counteven(int *a,int size)
{	int i;
	int n=0;
	for(i=0;i<size;i++)
	{
		if(a[i]%2==0)
		{
			n++;
		}

	}
	return n;
}
int main()
{
	int *a,i=0,n,e;
	printf("Enter length of array :");
	scanf("%d",&n);
	a=(int *)malloc(n * sizeof(int));
	for(i=0;i<n;i++)
	{
		printf("Enter a[%d]:",i+1);
		scanf("%d",(a+i));
	}
	for(i=0;i<n;i++)
	{

		printf("a[%d]=%d\n",i+1,*(a+i));
	}
	e=counteven(a,n);
	printf("\nTotal even no. in given array are %d\n",e);
	return 0;
}
  7. Write a function that returns a pointer to the maximum value of an array of double's. If the array is empty, return NULL. 
    double* maximum(double* a, int size);
    


    Ans.
    
#include <stdio.h>
double * maximum(double *a, int size)
{
	 double *tmp;
	 int i;
	 for(i=0;i<size;i++)
	 {
	 	 printf("\na[%d]=%0.2f\n",i+1,*(a+i));
	 }
	 for(i=0;i<size;i++)
	 {
		if(*(a+i) > *tmp)
		{
			tmp=(a+i);
		}
	 }
	 return tmp;
}
void main()
{
	double array[4] = {90.00,20.00,80.00,10.00};
	double *s;
	s=maximum(array,4);
	printf("\nThe largest number is : %0.2f \n",*s);
}
  8. Write a function myStrLen(char*) which returns the length of the parameter cstring.  Write the function without using the C function strlen. 
    Ans.
    
#include<stdio.h>
int mystrlen(char *s)
{
	int i=0;
	while(*(s+i) != '\0')
	{
		i++;
	}
	return i;
}
int main()
{
	char *s="This is it";
	int l;
	printf("%s",s);
	l=mystrlen(s);
	printf("The length of string is %d \n",l);
	return 0;
}
  9. Write a function contains(char*, char) which returns true if the 1st parameter cstring contains the 2nd parameter char, or false otherwise. 
    Ans.
    
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
int check(char *s,char j);
void main()
{
	char *s,j;
	int i,l=0;
	const MAX_LINE_SIZE = 256;
	char line[ MAX_LINE_SIZE ];
	printf("Enter String :");
	if (fgets( line, MAX_LINE_SIZE, stdin ) != NULL) 
	{
           s = malloc( strlen( line ) );
           strcpy( s, line );
        }
	printf("Enter Character :");
	scanf("%c",&j);
	l=check(s,j);
	if(l==1)
	printf("\ntrue");
	else
	printf("\nfalse");
}
int check (char *s,char j)
{
	int l=strlen(s)-1;
	int i;
	printf("%d",l);
	for(i=0;i<l;i++)
	{     
		if(*(s+i) == j)
		{
			return 1;
		}
	}
}
  10. Write a function revString(char*) which reverses the parameter cstring.  The function returns nothing. Complete the following code. 
    int main()
{
  char s[10] = "abcde";
  revString(s);  // call the function
  return 0;
}

void revtString(char* ptr)
{
  // WRITE YOUR CODE HERE
}

    Ans.
    
#include<stdio.h>
#include<string.h>
void revtString(char* ptr);
int main()
{
  char s[10] = "abcde";
  printf("This is before reversing %s\n ",s);
  revtString(s);  // call the function
  return 0;
}

void revtString(char* ptr)
{
  int i,l;
  l=strlen(ptr);
  printf("This is after reversing ");
  ptr +=l;
  for(i=0;i<=l;i++)
  {
      printf("%c",*ptr);
      ptr--;
  }
}
  11. swap_nums seems to work, but not swap_pointers. Fix it. 
    #include <stdio.h> 
void swap_nums(int *x, int *y) 
{ 
	int tmp; 
	tmp = *x; 
	*x = *y; 
	*y = tmp; 
} 
void swap_pointers(char *x, char *y) 
{ 
	char *tmp; 
	tmp = x; 
	x = y; 
	y = tmp; 
} 
int main() 
{ 
	int a,b; 
	char *s1,*s2; 
	a = 3; b=4; 
	swap_nums(&a,&b); 
	printf("a is %d\n", a); 
	printf("b is %d\n", b); 
	s1 = "I should print second"; 
	s2 = "I should print first"; 
	swap_pointers(s1,s2); 
	printf("s1 is %s\n", s1); 
	printf("s2 is %s\n", s2); 
	return 0; 
}

    Ans.
    
#include <stdio.h>
void swap_nums(int *x, int *y)
{
	int tmp;
	tmp = *x;
	*x = *y;
	*y = tmp;
}
void swap_pointers( char **x, char **y)
{
	char *tmp;
	tmp = (*x);
	(*x)=(*y);
	(*y)=tmp;
}
int main()
{
	int a,b;
	a = 3; b=4;
	char *s1,*s2;
	swap_nums(&a,&b);
	printf("a is %d\n", a);
	printf("b is %d\n", b);
	s1 = "I should print second";
	s2 = "I should print first";
	swap_pointers(&s1,&s2);
	printf("s1 is %s\n", s1);
	printf("s2 is %s\n", s2);
	return 0;
}
  12. Write a program to perform Matrix multiplication and Addtion using DMA( Dynamic memory allocation) 
    Ans.
    

#include<stdio.h>
#include<stdlib.h>
void main()
{
	int **a,**b,**m,**s;
	int i,j,k,r,c,r1,c1;
	printf("Enter size of row of  matrix A :");
	scanf("%d",&r);
	printf("Enter size of column of matrix A :");
	scanf("%d",&c);
	printf("Enter size of row of matrix B : ");
	scanf("%d",&r1);
	printf("Enter size of column of matrix B :");
	scanf("%d",&c1);
	a=(int **)malloc(r * sizeof(int));
	b=(int **)malloc(r1 * sizeof(int));
	for(i=0;i<r;i++)
	{
		a[i]=(int *)malloc(c * sizeof(int));
	}
	for(i=0;i<r1;i++)
	{
		b[i]=(int *)malloc(c1 * sizeof(int));
	}
	printf("\n\nEnter A:\n\n");
	for(i=0;i<r;i++)
	{
		for(j=0;j<c;j++)
		{       printf("Enter a[%d][%d]:",i,j);
			scanf("%d",*(a+i)+j);
		}
	}
	printf("\n\nEnter B:\n\n");
	for(i=0;i<r1;i++)
	{
		for(j=0;j<c1;j++)
		{       printf("Enter b[%d][%d]:",i,j);
			scanf("%d",*(b+i)+j);
		}
	}
	printf("\nMatrix A\n");
	for(i=0;i<r;i++)
	{
		for(j=0;j<c;j++)
		{
			printf("%d   ",*(*(a+i)+j));
		}
		printf("\n");
	}
	printf("\n Matrix B\n");
	for(i=0;i<r1;i++)
	{
		for(j=0;j<c1;j++)
		{
			printf("%d  ",*(*(b+i)+j));
		}
		printf("\n");
	}
	if(r==r1 && c==c1)
	{
		s=(int **)malloc(r * sizeof(int));
		for(i=0;i<r;i++)
		{
			s[i]=(int *)malloc(c * sizeof(int));
		}
		printf("\n\nSum of matrix.\n");
		for(i=0;i<r;i++)
		{
			for(j=0;j<c;j++)
			{
				 *(*(s+i)+j)=0;
				 *(*(s+i)+j)=*(*(a+i)+j) + *(*(b+i)+j);
			}
		}
		for(i=0;i<r;i++)
		{
			for(j=0;j<c;j++)
			{
				printf("%d\t",*(*(s+i)+j));
			} printf("\n");
		}
		free(s);
	}
	else
	{
		printf("\n\nSum of matrix is not possible.\n");
	}
	if(c==r1)
	{
		m=(int **)malloc(r * sizeof(int));
		for(i=0;i<r;i++)
		{
			m[i]=(int *)malloc(c * sizeof(int));
		}
		printf("\n\nMultiplication of matrix.\n");
		for(i=0;i<r;i++)
		{
			for(j=0;j<c;j++)
			{        *(*(m+i)+j)=0;
				for(k=0;k<c;k++)
				{
					*(*(m+i)+j)=*(*(m+i)+j)+*(*(a+i)+k) * *(*(b+k)+j);
				}

			}
		}
		for(i=0;i<r;i++)
		{
			for(j=0;j<c;j++)
			{
				printf("%d\t",*(*(m+i)+j));
			}
			 printf("\n");
		}
		free(m);
	}
	else
	{
		printf("\n\nMultiplication of matrix is not possible.\n");
	}
	free(a);
	free(b);
}
  13. Write a program to create array of pointer to hold 10 strings and sort it in ascending order. 
    Ans.
    
#include<string.h>
#include<stdlib.h>
void main()
{
	 char *s[10],*tmp;
	 int i,j;
	 for(i=0;i<10;i++)
	 {
		s[i]=(char *)malloc(10 * sizeof(char));
	 }
	 for(i=0;i<10;i++)
	 {
		printf("Enter String [%d] :",i+1);
		scanf("%s",s[i]);
	 }
	 for(i=0;i<10-1;i++)
	 {
		for(j=i+1;j<10;j++)
		{
			if(strcmp(s[i],s[j])>0)
			{
				tmp=s[i];
				s[i]=s[j];
				s[j]=tmp;
			}
		}
	 }
	 printf("\nRe-ordered Strings\n");
	 for(i=0;i<10;i++)
	 {
		printf("\n%s",s[i]);
	 }
}
  14. Write a program to input one string and a character , count how many times the character is occurred in the given string. 
    Ans.
    
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
void main()
{
	char *s;
	char j;
	int i,n=0;
	const MAX_LINE_SIZE = 256;
	char line[ MAX_LINE_SIZE ];
	printf("Enter String :");
	if (fgets( line, MAX_LINE_SIZE, stdin ) != NULL) 
	{
           s = malloc( strlen( line ) );
           strcpy( s, line );
        }
	printf("Enter the character you want to count :");
	scanf("%c",&j);
	for(i=0;i<strlen(s);i++)
	{       if(*(s+i) == j)
		n++;
	}
	printf("%c occurs %d times\n",j,n);
}