I've got a main program:
int main() {
char *str = "hello";
printf("%s\n", str);
/* Shift first byte 1 to get "iello" */
/* Have tried
str[0] >>= 8; */
printf("%s\n", str);
return 0;
}
Basically shift the first byte of the string up a byte to go from hello to iello or Hello to Iello
You can't modify a string literal, change it to:
char str[] = "hello"; //not string literal
printf("%s\n", str);
str[0]++; //add 1 to the first element
printf("%s\n", str);
char *str = "hello"; is a unmodifiable string literal.
The representation for h and i in ASCII for various bases are:
dec char bin hex oct
104. h 0110 1000 0x68 0150
105. i 0110 1001 0x69 0151
As you can see, bit 1 is flipped from h to i, so if you want to change it by bit operations one way would be:
#include <stdio.h>
int main(void)
{
char str[] = "hello";
printf("%s\n", str);
str[0] |= 0x01;
printf("%s\n", str);
return 0;
}
To use the increment use:
++str[0];
or:
char *p = str;
++*p;
Same, both increment and bit handling, goes for upper case.
If you work with the ASCII set there are other nice properties. As one example:
dec char bin hex oct
65. A 0100 0001 0x41 101o
66. B 0100 0010 0x42 102o
67. C 0100 0011 0x43 103o
68. D 0100 0100 0x44 104o
|
+--- flip bit 5 to switch between upper and lower case.
This goes for all alpha characters in the ASCII set.
97. a 0110 0001 0x61 141o
98. b 0110 0010 0x62 142o
99. c 0110 0011 0x63 143o
100. d 0110 0100 0x64 144o
Thus:
char str[] = "hello";
str[0] ^= 0x20;
printf("%s\n", str); /* Print Hello */
str[0] ^= 0x20;
printf("%s\n", str); /* Print hello */
Another one more frequently used, and which also is the same for e.g. EBCDIC, are the properties of numbers. They have ordered distance from 0, and in continuous range, so:
char num[] = "3254";
int n1 = num[0] - '0'; /* Converts char '3' to number 3 */
int n2 = num[1] - '0'; /* Converts char '2' to number 2 */
etc.
You can expand this for ASCII when converting string representation of hex values to numbers as the alpha characters are in order as well:
unsigned hex_val(char c)
{
if (c >= '0' && c <= '9')
return c - '0';
if (c >= 'a' && c <= 'f')
return c - 'a' + 10;
if (c >= 'A' && c <= 'F')
return c - 'A' + 10;
return ~0;
}
OK. I'll better stop there perhaps …
Do something like:
#include <stdio.h>
#include <ctype.h>
int main() {
char str[] = "hello";
printf("%s\n", str);
//str[0]=str[0]+1;
// to get uppercase letter include ctype.h header
str[0] = toupper(str[0] + 1);
printf("%s\n", str);
return 0;
}
