unit-5 String Math Date Time AI presentation

Programming in C
Unit 5 : String, Math and Date
Time Functions
Shalu J. Rajawat

Strings
• A special kind of array is an array of characters ending in the
null character 0 called string arrays
• A string is declared as an array of characters
char s[10]
char p[30]
• When declaring a string don’t forget to leave a space for the
null character which is also known as the string terminator
character
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"A String" A 0
g
n
i
r
t
S

Strings
4
String Literals
• String literal values are represented by sequences of
characters between double quotes (“)
• Examples
• “” - empty string
• “hello”
• “a” versus ‘a’
• ‘a’ is a single character value (stored in 1 byte) as the ASCII
value for a
• “a” is an array with two characters, the first is a, the second is
the character value 0

Strings
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Duplicate String Literals
• Each string literal in a C program is stored at a different
location
• So even if the string literals contain the same string, they are
not equal (in the == sense)
• Example:
• char string1[6] = “hello”;
• char string2[6] = “hello”;
• but string1 does not equal string2 (they are stored at different
locations)

String Variables
6
• Allocate an array of a size large enough to hold the string (plus 1 extra
value for the delimiter)
• Examples (with initialization):
char str1[6] = “Hello”;
char str2[] = “Hello”;
char *str3 = “Hello”;
char str4[6] = {‘H’,’e’,’l’,’l’,’o’,’0’};
• Note, each variable is considered a constant in that the space it is
connected to cannot be changed
str1 = str2; /* not allowable, but we can copy the contents
of str2 to str1 (more later) */

String Input
• Use %s field specification in scanf to read string
• ignores leading white space
• reads characters until next white space encountered
• C stores null (0) char after last non-white space char
• Reads into array (no & before name, array is a pointer)
• Example:
char Name[11];
scanf(“%s”,Name);
• Problem: no limit on number of characters read (need one for
delimiter), if too many characters for array, problems may occur.
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Operations on strings
8
• strcpy - copy one string into another
• strcat - append one string onto the right side of the other
• strcmp – compare alphabetic order of two strings
• strlen – return the length of a string
• Strrev-reverse the string
• Strupr- convert string to uppercase
• Strlwr- convert string to lowercase

Strcpy
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• strcpy(destinationstring, sourcestring)
• Copies sourcestring into destinationstring
For example
strcpy(str, “hello world”); assigns “hello world” to the string str
Code:
#include <stdio.h>
#include <string.h>
main()
{
char x[] = “Example with strcpy”;
char y[25];
printf(“The string in array x is %s n “, x);
strcpy(y,x);
printf(“The string in array y is %s n “, y);
}

Strcat
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 strcat(destinationstring, sourcestring)
 appends sourcestring to right hand side of destinationstring
For example if str had value “a big ”
strcat(str, “hello world”);
Appends “hello world” to the string “a big ” to get “ a big hello world”
Code:
#include <stdio.h>
#include <string.h>
main()
{
char x[] = “Example with strcat”;
char y[]= “which stands for string concatenation”;
strcat(x,y);
}

Mathematics Functions
All C inbuilt functions which are declared in “math.h” header file supports all the
mathematical related functions in C language. All the arithmetic functions used in C
language are given below.
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Function Description
floor ( )
This function returns the nearest integer which is less than or equal
to the argument passed to this function.
round ( )
This function returns the nearest integer value of the
float/double/long double argument passed to this function. If
decimal value is from “.1 to .5”, it returns integer value less than the
argument. If decimal value is from “.6 to .9”, it returns the integer
value greater than the argument.
ceil ( )
This function returns nearest integer value which is greater than or
equal to the argument passed to this function.
sin ( ) This function is used to calculate sine value.

Mathematics Functions
cos ( ) This function is used to calculate cosine.
cosh ( ) This function is used to calculate hyperbolic cosine.
exp ( ) This function is used to calculate the exponential “e” to the xth power.
tan ( ) This function is used to calculate tangent.
tanh ( ) This function is used to calculate hyperbolic tangent.
sinh ( ) This function is used to calculate hyperbolic sine.
log ( ) This function is used to calculates natural logarithm.
log10 ( ) This function is used to calculates base 10 logarithm.
sqrt ( )
This function is used to find square root of the argument passed to
this function.
pow ( ) This is used to find the power of the given number.
trunc.(.)
This function truncates the decimal value from floating point value
and returns integer value.
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Program for Mathematics Function
// C code to illustrate
// the use of math function
#include <stdio.h>
#include <math.h>
int main ()
{
double x = 0, val4 = -2.3, x=2.7, ret;
int b = -344, c =3;
printf("The exponential value of %lf is %lfn", x, exp(x));
printf("The exponential value of %lf is %lfn", x+1, exp(x+1));
printf("The exponential value of %lf is %lfn", x+2, exp(x+2));
printf ("value4 = %.1lfn", ceil(val4));
printf("Value4 = %.1lfn", floor(val4));
printf("The absolute value of %d is %lfn", b, fabs(b));
ret = log(x);
printf("log(%lf) = %lf", x, ret);
x = 10000;
/* finding value of log1010000 */
ret = log10(x);
printf("log10(%lf) = %lfn", x, ret);
printf("Remainder of %f / %d is %lfn", x, c, fmod(x, c));
return(0);
}
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Date & Time Function
Date &Time functions in C are used to interact with system date & time routine and
formatted time outputs are displayed. Example programs for the date & time functions
are given below.
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Date and Time Functions
setdate() This function used to modify the system date
getdate() This function is used to get the CPU time
clock() This function is used to get current system time
time() This function is used to get current system time as structure
difftime() This function is used to get the difference between two given times
strftime() This function is used to modify the actual time format
mktime() This function interprets tm structure as calendar time
localtime()
This function shares the tm structure that contains date and time
informations
gmtime()
This function shares the tm structure that contains date and time
informations
ctime()
This function is used to return string that contains date and time
informations
asctime()
Tm structure contents are interpreted by this function as calendar time. This
time is converted into string.
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setDate
#include<stdio.h>
#include<dos.h>
#include<conio.h>
int main()
{
struct date dt;
printf("Enter new date in the format(day month year)");
scanf("%d%d%d",&dt.da_day,&dt.da_mon,&dt.da_year);
setdate(&dt);
printf("Now, current system date is %d-%d-%dn” ,dt.da_day,dt.da_mon,dt.da_year);
return 0;
}
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getDate()
#include<stdio.h>
#include<dos.h>
int main()
{
struct date dt;
getdate(&dt);
printf("Operating system's current date is %d-%d-%dn"
,dt.da_day,dt.da_mon,dt.da_year);
return 0;
}
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Clock()
#include <stdio.h>
#include <time.h>
#include <math.h>
int main()
{
int i;
clock_t CPU_time_1 = clock();
printf("CPU start time is : %d n", CPU_time_1);
for(i = 0; i < 150000000; i++);
clock_t CPU_time_2 = clock();
printf("CPU end time is : %d", CPU_time_2);
}
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Time() & Difftime()
#include <stdio.h>
#include <time.h>
int main ()
{
time_t seconds;
seconds = time (NULL);
printf ("Number of hours since 1970 Jan 1st " "is %ld n", seconds/3600);
return 0;
}
#include <stdio.h>
#include <time.h>
int main()
{
time_t begin,end;
long i;
begin= time(NULL);
for(i = 0; i < 150000000; i++);
end = time(NULL);
printf("for loop used %f seconds to complete the " "executionn", difftime(end, begin));
return 0;
}
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Remaining Functions
#include <stdio.h>
#include <time.h>
#define LEN 150
int main ()
{
char buf[LEN];
time_t curtime;
struct tm *loc_time;
//Getting current time of system
curtime = time (NULL);
// Converting current time to local time
loc_time = localtime (&curtime);
// Displaying date and time in standard format
printf("%s", asctime (loc_time));
strftime (buf, LEN, "Today is %A, %b %d.n", loc_time);
fputs (buf, stdout);
strftime (buf, LEN, "Time is %I:%M %p.n", loc_time);
fputs (buf, stdout);
return 0;
}
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Summary
• C is a general-purpose programming language.
• C is a high-level language that is easy to read, understand and maintain
• C programs can be reused.
• C needs a compiler to convert its programs into machine readable form
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