Pointers and Strings Examples

Command line input:

#include <stdio.h>
 
int main(int argc,char *argv[])
{
    int i;
    for (i=0;i<argc;i++)
        printf("%s ",argv[i]);
    printf("\n");
    return 0;
}

Another example

#include <stdio.h>
 
int main(int argc,char *argv[])
{
    int i;
 
    for (i=1;i<argc;i++)
        printf("%s ",argv[i]);
    printf("\nName of file is: %s\n",argv[0]);
    printf("Number of parameters :%d\n",argc);
    return 0;
}

Example function for copying a signed integer into a string; 

void ITOS(long x, char *ptr) 
{ 
	/* Convert a signed decimal integer to a string */ 

	long pt[9] = { 100000000, 10000000, 1000000, 100000, 10000, 1000, 100, 10, 1 }; 
	int n; 

	/* Check sign */ 
	if (x < 0)
	{ 
		*ptr++ = '-'; 
		/* Convert x to absolute */ 
		x = 0 - x; 
	} 

	for(n = 0; n < 9; n++)
	{ 
		if (x > pt[n])
		{ 
			*ptr++ = '0' + x / pt[n]; 
			x %= pt[n]; 
		} 
	} 
	return; 
} 

more useful example of pointers

#include <stdio.h>

main()
{
	int n;
	int a[25];
	int *x;

	/* x is a pointer to an integer data type */

	/* Assign x to point to array element zero */
	x = a;

	/* Assign values to the array */
	for(n = 0; n < 25; n++)
		a[n] = n;


	/* Now print out all array element values */
	for(n = 0; n < 25; n++ , x++)
		printf("\nElement %d holds %d",n,*x);
}

using strings pointers and functions

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

main()
{
	char data[80];
	char *p;
	char name[30];
	int age;

	printf("\nEnter your name and age ");
	/* Read in a string of data */
	gets(data);


	/* P is a pointer to the last character in the input string */
	p = &data[strlen(data) - 1];

	/* Remove any trailing spaces by replacing them with null bytes */
	while(*p == ' '){
		*p = 0;
		p--;
	}

	/* Locate last space in the string */
	p = strrchr(data,' ');

	/* Read age from string and convert to an integer */
	age = atoi(p);

	/* Terminate data string at start of age field */
	*p = 0;

	/* Copy data string to name variable */
	strcpy(name,data);

	/* Display results */
	printf("\nName is %s age is %d",name,age);
}

pointers to function example

#include <stdio.h> 
#include <math.h> 

double (*fp[7])(double x); 

void main()
{ 
	double x; 
	int p; 

	fp[0] = sin; 
	fp[1] = cos; 
	fp[2] = acos; 
	fp[3] = asin; 
	fp[4] = tan; 
	fp[5] = atan; 
	fp[6] = ceil; 

	p = 4; 

	x = fp[p](1.5); 
	printf("\nResult %lf",x); 
} 

changing const array by redirection

#include <stdio.h>

int funca(const int x[])
{
	int *ptr;
	int n;

	/* This line gives a 'suspicious pointer conversion warning' */
	/* because x is a const pointer, and ptr is not */
	ptr = x;

	for(n = 0; n < 100; n++)
	{
		*ptr = n;
		ptr++;
	}
}

main()
{
	int array[100];
	int counter;

	funca(array);

	for(counter = 0; counter < 100; counter++)
		printf("\nValue of element %d is %d",counter,array[counter]);
}

string functions using pointers

**********************************************************************/
//function to calculate the length of string
/**********************************************************************/
int strlen(char *s)
{
char *p=s;
while (*p++);
return p-s-1;
}

/**********************************************************************/
//function to copy one string to another
/**********************************************************************/
void strcpy(char *d,char *s)
{
while(*d++ = *s++);
}

/**********************************************************************/
//function to add one string to the end of the other
/**********************************************************************/
void strcat(char *d,char *s)
{
while (*d++);
d--;
while (*d++ = *s++);
}

//stristr() function
#include<stdio.h>
#include<string.h>
char *stristr(char *s1, char *s2)
{
	char c1[1000];
	char c2[1000];
	char *p;

	strcpy(c1,s1);
	strcpy(c2,s2);

	strupr(c1);
	strupr(c2);

	p = strstr(c1,c2);
	if (p)
		return s1 + (p - c1);
	return NULL;
}
void main()
{
char *a="Haifa Computers";
printf("%s\n",stristr(a,"haifa"));
}

String Library

/**********************************************************************/
//string library
/**********************************************************************/
#include<string.h>
#include<stdio.h>
#include<conio.h>
#include<io.h>

/**********************************************************************/
//this function print message in the center of the screen
/**********************************************************************/

int center(char *str,int row)
{
	int len=strlen(str);
	if (len>80)
		return -1;
	gotoxy((80-len)>>1,row);
	write(1,str,len);
	return 0;
}

/**********************************************************************/
//this function take n characters from the right side of the source
//string and copy it to the destination string
/**********************************************************************/
char *rightstr(char *d,char *s,int num)
{
	char *temp;
	int len=strlen(s);
	if (len<num)
		return NULL;
	temp=d;
	s+=len-num;
	while (*d++=*s++);
	return temp;
}


/**********************************************************************/
//this function copy part of string src to string dest
/**********************************************************************/
char *midstr(char *d,char *s,int start,int num)
{
char *temp;
int len=strlen(s),offset;
if (len<num+start) return NULL;
if (num==0)
	num=len-start+1;
temp=d;
offset=start-1;
do{
	*d++=*(s+offset);
}while(*s++ && num--);
*(d-1)='\0';
return temp;
}

/**********************************************************************/
//this function delete all the charecters c in string s
/**********************************************************************/
void strdelc(char *s,char c)
{
while (*s)
	{
	if(*s==c)
		strcpy(s,s+1);
	else
		s++;
	}
}

/**********************************************************************/
//this function delete the char. c from string s ,just n times
/**********************************************************************/
void strdelcn(char *s,int n,char c)
{
 while(*s)
	{
	if (*s==c && n)
		{
		strcpy(s,s+1);
		n--;
		}
	else
		s++;
	}
}

/**********************************************************************/
//this function replace all the charecters old to new
/**********************************************************************/
void strrep(char *s,char newc ,char oldc)
{
char *ptr;
int len=strlen(s);
while (len)
{
	ptr=(char *)memchr(s,oldc,len);//func. memchr returns pointer to char old if found
	if (ptr)
	{
		*ptr=newc;
		len-=(ptr-s);
		s=ptr+1;
	}
	else
		return;
}
}

void main(void)
{
clrscr();
char l[35],p[]="hello world what a nice day";
strrep(p,'p','l');
center(p,5);
getch();
}

An example program to reverse all the characters in a string

#include <stdio.h>
#include <string.h>

char *strrev(char *s)					
{
	/* Reverses the order of all characters in a string except the null */
	/* terminating byte */

	char *start;
	char *end;
	char tmp;

	/* Set pointer 'end' to last character in string */
	end = s + strlen(s) - 1;

	/* Preserve pointer to start of string */
	start = s;

	/* Swop characters */
	while(end >= s)
	{
		tmp = *end;
		*end = *s;
		*s = tmp;
		end--;
		s++;
	}
	return(start);
}


void main()
{
	char text[100];
	char *p;

	strcpy(text,"This is a string of data");

	p = strrev(text);

	printf("\n%s",p);
}

example of strtok() function

#include <stdio.h> 
#include <string.h> 

void main()
{ 
	char data[50]; 
	char *p; 

	strcpy(data,"RED,ORANGE,YELLOW,GREEN,BLUE,INDIGO,VIOLET"); 

	p = strtok(data,","); 
	while(p)
	{ 
		puts(p);
		p = strtok(NULL,","); 
	}; 
} 
/* using for loop *************************************\

	for(strtok(data,","); p; p = strtok(NULL,","))
	{ 
		puts(p);
	}; 
\******************************************************/

strupr and strlwr examples using pointers

#include<stdio.h>
#include<ctype.h>
#include<string.h>

void strupper(char *source)
{
	char *p;

	p = source;
	while(*p)
	{
		*p = toupper(*p);
		p++;
	}
}

void strlower(char *source)
{
	char *p;

	p = source;
	while(*p)
	{
		*p = tolower(*p);
		p++;
	}
}


void main()
{
	char name[50];

	strcpy(name,"Servile Software");

	printf("\nName equals %s",name);

	strupper(name);

	printf("\nName equals %s",name);

	strlower(name);

	printf("\nName equals %s",name);
}