Data Conversion
The following functions convert data types:
atof() converts an ASCII character to a double (to float
in c++)
atoi() converts an ASCII character to an integer
atol() converts an ASCII to a long integer
itoa() converts an integer to a character array
Example:
/* convert a string to an integer */
#include <stdio.h>
#include <stdlib.h>
char string[] = “1234”;
int main(void)
{
int sum;
sum = atoi( string);
printf(“Sum = %d\n”,
sum);
return 0;
}
Another example:
/* convert a string to an integer */
#include <stdio.h>
#include <stdlib.h>
int main(void) //
remember that the default return data is int
{
int sum;
char buff[20];
printf(“Enter in an integer
“);
scanf (“%d”, &sum);
printf(“As a string it is
%s\n”, itoa(sum, buff, 10));
return 0;
}
Note that itoa() takes three parameters:
• The integer to be converted
• A character buffer into which the resultant string
is stored
• A radix value (10=decimal, 16=hexadecimal);
Built in functions for string handling:
string.h
The following macros are built into the file string.h
strcat appends
a string
strchr finds
first occurrence of a given character
strcmp compares
two strings
strcmpi compares
two strings, non-case sensitive
strcpy copies
one string to another
strlen finds
the length of a string
strlwr converts
a string to lowercase
strncat appends
n characters of string
strncmp compares n characters
of two strings
strncpy copies
n characters of one string to another
strrchr
finds last occurrence of given character in string
strrev
reverses string
strset sets
all characters of string to a given character
strspn finds
first sub string from given character set in string
strupr converts
string to uppercase
To copy one string to another
#include <stdio.h>
#include <string.h>
int main(void)
{
const char yes = ‘y’
char reply;
char garment[] = “overcoat”;
printf(“Is it raining outside?
Answer y/n \n”);
scanf(“%c”, &reply);
if (reply == yes)
strcpy
(garment, “raincoat”);
printf(“before you go out
today take your %s\n”, garment);
return 0;
}
To covert a string to uppercase
#include <stdio.h>
#include <string.h>
int main(void)
{
char name[80]; /*
declare an array of characters 0 – 79 */
printf(“Enter in a name
in lowercase\n”);
scanf(“%s”, &name);
strupr(name);
printf(“The name in uppercase
is %s\n”, name);
return 0;
}
Sample program output
Enter in a name in lowercase
samuel
The name in uppercase in SAMUEL
Built in functions for character handling
The following character handling functions are defined
in ctype.h
isalnum
tests for alphanumeric character
isalpha
tests for alphabetic character
isascii
tests for ASCII character
iscntrl
tests for control character
isdigit
tests for 0 to 9
isgraph
tests for printable character
islower tests
for lowercase
isprint
tests for printable character
ispunct
tests for punctuation character
isspace
tests for space character
isupper
tests for uppercase character
isxdigit tests
for hexadecimal
toascii converts
character to ASCII code
tolower converts
character to lowercase
toupper
converts a character to uppercase
To convert a string array to uppercase one character
at a time using touper()
#include <stdio.h>
#include <ctype.h>
int main(void)
{
char name[80];
int loop;
printf(“Enter in a name
in lowercase\n”);
scanf(“%s”, &name);
for (loop = 0; name[loop] !=0;
loop++)
name[loop]
= toupper(name[loop]);
printf(“The name in uppercase
is |%s\n”, name);
return 0;
}
Sample program output
Enter in a name in lowercase
samuel
The name In uppercase in SAMUEL
Don't worry if this lesson seems too complicated. Pay attention
only to the keywords that are summarized in the bullet points
on top of this page.
A new section is under construction which will list all
the standard libraries (as defined by ASCII) and will sort
all keywords alphabetically and by library.
back to top back
to lesson 11 go
to lesson 13
