1

Strings

While C supplies the data type char, it does not have a

data type for character strings;

A character string must be represented as one of the

following:

As an array of characters: char myname[20];

As a pointer to char: char *p;

As a string literal: "Hi There!"

All three representations are pointers to char.

The array uses one cell for each character in the string,

with the final cell holding the null character ‘\0’

2

Strings

The C-string "Hi there!" would be stored in memory as

shown:

Note that for each array, there are one more cells than the

number of characters

When you use double quotes to list the initial values of the

character array, the system will automatically add the null

terminator ‘\0’

Using an unsized array is better in these cases

Remember that the array’s dimension must be large

enough to hold the string along with the null terminator

3

Strings

/* A C program to read string from console / terminal */

#include <stdio.h>

int main( )

{

char name[20];

printf("Enter name: ");

scanf("%s", name);

printf("Your name is %s.", name);

return 0;

}

/* Program Output*/ Enter name: Abdus Salam

Your name is Abdus.

4

Strings

/* Program to read read line of text manually from console / terminal */

#include <stdio.h>

int main(){

char name[30],ch;

int i=0;

printf("Enter name: ");

while(ch!='\n') { // terminates if user hit enter

ch=getchar();

name[i]=ch;

i++; }

name[i]='\0'; // inserting null character at end

printf("Name: %s.”, name);

return 0;

}

/* Program Output*/ Enter name: Abdus Salam //hit enter

Your name is Abdus Salam.

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Strings

/* Predefined functions gets() and puts() to read and display string

respectively from console / terminal */

int main()

{

char name[30];

printf("Enter name: ");

gets(name); //Function to read string from user.

printf("Name: ");

puts(name); //Function to display string.

return 0;

}

/* Program Output*/ Enter name: Abdus Salam //hit enter

Your name is Abdus Salam.

6

Strings

#include <stdio.h>

int main ( ) {

char water_state1 [4] = {‘g’,’a’,’s’,’\0’}; //null terminated character array, i.e. a string

char water_state2 [6]; // if null terminated, then represents a 5 character string

char water_state3 [7] = “liquid”; // character array initialized with string literals

printf (“\n\tPlease enter the water state: ”);

scanf (“%s”, water_state2);

printf (“%s\n”, water_state1);

printf (“%s\n”, water_state2);

printf (“%s\n”, water_state3);

return 0;

}

/* Program Output*/ Please enter the water state: // type solid and hit enter

gas

solid

liquid.

7

Strings

Note that in the scanf function, water_state2 was not

preceded by the address operator &

Unlike simple variable names, array’s name is an address

expression – the address of the first element in the array

Remember that strings are character arrays terminated

by a null character ‘\0’. But character arrays without a

terminating null character is possible. Therefore,

although “all strings are character arrays but all character

arrays are not strings”.

8

Strings

Array of char can be defined and initialized to a C-string

char str1[20] = "hi";

A pointer to a string can be declared and then initialized

to a C-string

char *pStr;

pStr = "hello there!";

Array of char can be defined and later have a string

copied into it

char str2[20];

strcpy(str2, "hi");

9

Strings

Library Functions for Working with C-Strings require

<string.h> header file

Functions take one or more C-strings as arguments.

Argument can be:

Name of an array of char

pointer to char

literal string

int strlen(char *str) - returns length of a C-string:

int n = strlen("hello"); // n = 5

Note: This is the number of characters in the string, NOT

the size of the array that contains it

10

Strings

strcat(char *dest, char *source) - takes two C-strings as

input. It adds the contents of the second string to the

end of the first string:

char str1[15] = "Good ";

char str2[30] = "Morning!";

strcat(str1, str2);

printf ( “%s”, str1); // prints: Good Morning!

No automatic bounds checking: programmer must

ensure that str1 has enough room for result

11

Strings

strcpy(char *dest, char *source) - copies a string from a

source address to a destination address

char name[15];

strcpy(name, "Deborah");

printf (“%s”, name); // prints Deborah

Using pointer to string:

char *p;

strcpy(p, "Deborah");

printf (“%s”, p); // prints Deborah

12

Strings

int strcmp(char *str1, char*str2) - compares strings stored

at two addresses to determine their relative alphabetic

order:

Returns a value:

less than 0 if str1 precedes str2

equal to 0 if str1 equals str2

greater than 0 if str1 succeeds str2

Often used to test for equality

if(strcmp(str1, str2) == 0)

printf (“equal“);

else

printf ("not equal“);

13

Strings

strcmp is also used to determine ordering of C-strings in

sorting applications

Note that C-strings cannot be compared using == (compares

addresses of C-strings, not contents)

char *strstr(char *str1, char *str2) - searches for the

occurrence of str2 within str1.

Returns a pointer to the occurrence of str2 within str1 if

found, and returns NULL otherwise

char s[15] = "Abracadabra";

char *found = strstr(s, "dab");

printf(“%s”, found); // prints dabra

14

Strings

char *strchr(char *str1, char ch) - searches for the

occurrence of ‘ch’ within str1.

Returns a pointer to the first occurrence of ‘ch’ within str1 if

found, and returns NULL otherwise

char *p1, *p2;

char s[15] = "Abracadabra";

p1 = strchr(s, ‘d’);

if (p1 == NULL) printf(“\n no match found”);

printf(“ \’ %c \’ found”, *p1); // prints ‘d’ found

p2 = strchr(s, ‘t’);

if (p2 == NULL) printf(“\n no match found”);

printf(“%c found”, *p2); // prints no match found

15

Strings

char *strlwr(char *str) - Converts string ‘str’ to lowercase

char *strupr(char *str) - Converts string ‘str’ to uppercase

char *p1, *p2;

char s[15] = "Abracadabra";

p1 = strupr(s);

printf(“ %s \n”, p1); // prints ABRACADABRA

p2 = strlwr(s);

printf(“%s \n”, p2); // prints abracadabra

16

Strings

/* Program to sort words in Dictionary Order from console / terminal */

#include<stdio.h>

#include <string.h>

int main(){

int i,j;

char str[10][50],temp[50];

printf("Enter 10 words:\n");

for(i=0;i<10;++i)

gets(str[i]);

for(i=0;i<9;++i)

for(j=i+1;j<10 ;++j){

if(strcmp(str[i],str[j])>0)

{

strcpy(temp,str[i]);

strcpy(str[i],str[j]);

strcpy(str[j],temp);

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Strings

}

}

printf("In lexicographical order: \n");

for(i=0;i<10;++i){

puts(str[i]);

}

return 0;

}

/* Program Output*/

Enter 10 words:

fortran

java

perl

python

php

javascript

18

Strings

c

cpp

ruby

csharp

In lexicographical order:

c

cpp

csharp

fortran

java

javascript

perl

php

python

ruby

19

Strings

Conversion Functions can be used to convert between string

and numeric forms of numbers. These functions require

<stdlib.h> header file

atoi() converts alphanumeric to int

atol() converts alphanumeric to long

Prototypes:

int atoi(char *numericStr)

long atol(char *numericStr)

Examples:

int number; long lnumber;

number = atoi("57");

lnumber = atol("50000");

20

Strings

atof() converts a numeric string to a floating point number,

actually a double

Prototype:

double atof(char *numericStr)

Example:

double dnumber;

dnumber = atof("3.14159");

if C-string being converted contains non-digits, results are

undefined

function may return result of conversion up to first non-digit

function may return 0

21

Strings

itoa() converts an int to an alphanumeric string

Allows user to specify the base of conversion

itoa(int num, char *numStr, int base)

Example: To convert the number 1200 to a hexadecimal

string

char numStr[10];

itoa(1200, numStr, 16);

The function performs no bounds-checking on the array

numStr

22

Strings

FUNCTION MEANING

isalpha() true if arg. is a letter, false otherwise

isalnum() true if arg. is a letter or digit, false otherwise

isdigit() true if arg. is a digit 0-9, false otherwise

islower() true if arg. is lowercase letter, false

otherwise

Character Testing Functions: - require <ctype.h> The following functions takes a single character as argument, e.g., isalpha(‘z’); //Output: true, i.e., 1

23

Strings

FUNCTION MEANING

isprint() true if arg. is a printable character, false

otherwise

ispunct() true if arg. is a punctuation character, false otherwise

isupper() true if arg. is an uppercase letter, false

otherwise

isspace() true if arg. is a whitespace character, false

otherwise

24

Strings

FUNCTION MEANING

toupper() convert a single letter to uppercase equivalent.

if char argument is lowercase letter, return

uppercase equivalent; otherwise, return input unchanged

tolower() convert a single letter to lowercase equivalent.

if char argument is uppercase letter, return

lowercase equivalent; otherwise, return input unchanged

Character Case Conversion Functions - require <ctype.h> Examples: toupper(‘z’); //Output: Z toupper(‘Z’); //Ouput: Z

25

Strings

Character Case Conversion Functions - Examples - require <ctype.h> header file

char s[] = "Hello!";

printf(“%c”, toupper(s[0]); //displays 'H'

printf(“%c”, toupper(s[1]); //displays 'E'

printf(“%c”, toupper(s[5]); //displays '!'

char s[] = "Hello!";

printf(“%c”, tolower(s[0]); //displays 'h'

printf(“%c”, tolower(s[1]); //displays 'e'

printf(“%c”, tolower(s[5]); //displays '!'

26

Strings

Standard input and output functions that use character arrays as function arguments are:

gets(), puts() // console I/O functions

fgets(), fputs() // file I/O functions

sscanf(), sprintf () // string I/O functions

The following program uses string I/O functions

#include <stdio.h>

#define SIZE 20

int main ( ) {

char test_array [SIZE];

27

Strings

fputs (“Please enter the first string : “, stdout);

gets (test_array);

fputs (“The first string entered is : “, stdout);

puts (test_array);

fputs (“Please enter the second string : “, stdout);

fgets (test_array, SIZE, stdin);

fputs (“The second string entered is : “, stdout);

fputs (test_array, stdout);

sprintf (test_array, “This was %s a test”, “just”);

fputs (“sprintf() created : “, stdout);

fputs (test_array, stdout);

return 0;

}

28

Strings

The output from the first run of the program looks like:

Please enter the first string : string one

The first string entered is : string one

Please enter the second string : string two

The second string entered is : string two

sprintf() created : This was just a test

Take care when running the program

The gets() function receives characters from standard input (stdin, the keyboard by default) and places them into the array whose name is passed to the function

When one presses ENTER to terminate the string, a newline character is transmitted which is changed into a null character by gets() function

29

Strings

The puts() function echoes to the terminal just what was entered with gets()

When you use the fgets() function, you can guarantee a maximum number of input characters

This function stops reading the designated file stream when one fewer characters are read than the second argument specifies

The fgets() function does not eliminate the newline character, as gets() did, but merely appends the null character so that a valid string is stored

Much like gets() and puts(), fgets() and fputs() are symmetrical

fgets() does not eliminate the newline character, nor does fputs () add one

30

Strings

The function sprintf(), which stands for ‘string printf()’, uses

a control string with conversion characters, just like printf()

However, sprintf() places the resulting formatted data in a

string rather than immediately sending the result to the

standard output

This can be beneficial if the exact same output must be

created twice – for example, when the same string must

be output to both the display monitor and the printer

Likewise, the function sscanf(), stands for ‘string scanf()’, uses a

control string with conversion characters, just like scanf()

However, sscanf() scans for the specified formatted data in

a string rather than receiving the data from the standard input

This helps to compress the input data by eliminating characters

which are used in the input buffer only as data separators.

31

Strings

Syntax:

sprintf ( char *string, “control string”,

variables/expression/constants ) ;

sscanf ( char *string, “control string”, &variables ) ;

Example: Given, i = 10, f = 3.50, string2[] = “20 3.75”

sprintf (string1, “%d %f\n”, i, f); //string1 = “10 3.50”;

sscanf (string2, “%d %f”, &i, &f); // i = 20; f = 3.75;

Here, sprintf() places the formatted output to the string1,

NOT to the standard output (display)

Similarly, sscanf() reads data from the string2, NOT from the

standard input (keyboard)

32

Strings

// Program 1

#include <stdio.h>

#include <string.h>

#define WORD_LENGTH 6

#define STRING_LENGTH 20

int main ()

{

char part1 [WORD_LENGTH] = "In",

part2 [WORD_LENGTH] = " the ",

prologue [STRING_LENGTH];

strcpy (prologue, part1);

strcat (prologue, part2);

strcat (prologue, "beginning ... ");

33

Strings

printf ("%s\n", prologue);

return 0;

}

// Program 2

#include <stdio.h>

#include <string.h>

int main ()

{

char string1 [] = "one", string2 [] = "one";

int result = 0;

34

Strings

if (strlen (string2) >= strlen (string1))

result = strcmp (string1, string2);

printf ("The string %s", result == 0 ? "was" : "wasn't");

printf (" found to be equal");

return 0;

}

The first program outputs

In the beginning ...

And the second program outputs

The string was found to be equal

35

Strings

// Program to PLOT a function in Text Mode Output Screen

#include <stdio.h>

#include <math.h>

#define X_MAX 76 //X_MAX = 60, VERTICAL RESOLUTION (ROW), 0 AT TOP LEFT

#define Y_MAX 31 //Y_MAX = 80, HORIZONTAL RESOLUTION (COLUMN), 0 AT TOP LEFT

#define SYMBOL 'o'

#define X_TITLE "Compression Ratio, r (8 to 12)"

#define Y_TITLE "Efficiency (56% to 71%)"

#define PLOT_TITLE "FIGURE: Otto Cycle Efficiency vs Compression Ratio"

#define Y_F(X) 100*(1 - (1 /(pow((X), 0.4)))) //MACRO FUNCTION: ARGUMENTS ALWAYS NEED

PARENTHESIS

36

Strings

int main(){

char plot[X_MAX][Y_MAX];

int x, y;

for (x = 0; x < X_MAX; x++){

for(y = 0; y < Y_MAX; y++){

plot[x][y] = ' ';

}

}

printf("\n\n");

for(x = 8; x <= 22; x++) {

y = (int) roundf (Y_F(x)); //THE EXPRESSION IS TYPE CASTED TO INT

plot[X_MAX - y][Y_MAX - x] = SYMBOL; //BOTH AXIS INVERSIONS //ARE DONE TO PLOT

//BOTTOM UP

}

37

Strings

for (x = 0; x < 31; x++) {

plot[x][25] = '|';

}

printf("\n\n\t%s", Y_TITLE );

for (x = 0; x < 25; x++) {

printf("\n\t");

for(y = 26; y > 5; y--){

printf("%c ", plot[x][y]);

}

}

printf("\n\t _______________________________________________");

printf("\n\n\t\t\t%s", X_TITLE);

printf("\n\n\t %s\n\n", PLOT_TITLE );

printf("\n\n");

return 0;

}

38

Strings

// Output of the previous PLOT program in Text Mode Output Screen

39

Strings

// Let us PLAY a simple WORDGAME

#include <stdio.h>

#include <stdlib.h> //DECLARES SRAND(), RAND(), SYSTEM() FUNCTIONS

#include <string.h>

#include <ctype.h>

#include <time.h> //DECLARES TIME() FUNCTION

char *newword(); //FUNCTION PROTOTYPE TO GENERATE NEW WORD

int main(){ //MAIN GAME ENGINE

char ch, ch1, choice;

char gameword[20]={'\0'}; //MAIN GAMEWORD

char guesses[20]={'\0'}; //PLAYER GUESSWORD

int n, i, j, trial, check_repeat, repeat=0, ok =0;

srand(time(NULL));

40

Strings

for (; ;) {

sprintf(gameword, "%s", newword()); //SAVES A NEW WORD TO 'gameword'

n = strlen(gameword);

trial = n + 5; //TOTAL NUMBER OF GUESSES ALLOWED TO THE PLAYER

system("cls"); //SYSTEM COMMAND TO CLEAR THE OUTPUT SCREEN

printf("\n\n\n");

printf("\n\tGuess a country name of %d characters\n\n\t\tpress enter after each character...(a - z):\n\n\n\t ", n);

for(j = 1; j <= trial; j++){

printf("\n\n\t\t");

ch = toupper(getchar());

ch1=getchar();

check_repeat = 0;

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Strings

for(i = 0; i < n; i++){

if(ch == gameword[i]){

guesses[i]= ch;

ok++; //COUNTS TOTAL NUMBER OF CORRECT GUESSES

check_repeat++;

if(check_repeat>1) repeat++;

}

}

system("cls");

printf("\n\n\t\t");

for(i = 0; i <= n; i++)printf("%c", guesses[i]);

printf("\t\t(%d characters remain)\n", (n - ok));

printf("\n\n\t\t%d guesses remain...\n", trial-j);

printf("\n\t\tCorrect guesses: %d", ok);

printf("\t\tMisses: %d\n\n\n\n\t", (j - ok));

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Strings

if(strcmp(guesses, gameword) == 0) goto exit1;

}

system("cls");

printf("\n\n\t\t");

for(i = 0; i <= n; i++) printf("%c", gameword[i]);

printf("\t\t(%d characters remained...)\n", (n - ok));

printf("\n\n\t\tYou have lost!!...Try out next time...\n");

printf("\n\n\t\t%d guesses remained...\n", trial - j);

printf("\n\t\tCorrect guesses: %d", ok);

printf("\t\tMisses: %d\n\n\n\n\t", (j - ok));

goto end;

exit1:

system("cls");

printf("\n\n\t\t");

43

Strings

for(i = 0; i <= n; i++) printf("%c", gameword[i]);

printf("\n\n\t\tCongrats!! You have won!!!");

printf("\n\n\t\t%d guesses remained...\n", trial - j);

printf("\n\t\tCorrect guesses: %d", ok);

printf("\t\tMisses: %d", (j - ok));

end:

printf("\n\n\t\tPlay again? (Y/N) ");

choice = toupper(getchar());

if( choice == 'N')break;

for(i=0; i<20; i++) guesses[i]='\0';

ok=0;

}

printf("\n\n");

return 0;

} // MAIN GAME ENGINE ENDS HERE

44

Strings

char *newword() { //FUNCTION RETURN TYPE IS POINTER TO STRING

int m; //USE THIS FUNCTION TO EXTEND THE GAME

select:

m = rand()%11;

switch(m) {

case 0: goto select;

case 1: return "BANGLADESH";

case 2: return "BHUTAN";

case 3: return "JAPAN";

case 4: return "SRILANKA";

case 5: return "SINGAPORE";

case 6: return "ARGENTINA";

case 7: return "BRAZIL";

case 8: return "AUSTRALIA";

case 9: return "IRAQ";

case 10: return "PALESTINE"; } }

45

Strings

// Output of the WORDGAME at different steps