String?

[Ilir Selmani]

How to replace string in C.. i need to replace
'a' --> 'z'
'b' --> 'y' ... first letter with last, second...

[Alpo]

Are you saying you need to reverse the string? Your explanation was very terse.

You might be able to reverse it using the general swap technique:

    char String[] = "Ride The Snake!";

    int i = 0;

    int range = strlen(String) - 1;

    for(int j = range; i < (range/2), j > (range/2); i++, j--)
    {
        if(String[i] == NULL || String[j] == NULL)
        {
            break;
        }
        else
        {
            char temp = String[j];

            String[j] = String[i];

            String[i] = temp;
        }
    }

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

Edit:

The swap technique basically goes like this. You take an intermediate variable of the correct type (temp), then assign it with one of the variables needing swapping ( String [j] ). Once this is done, you are free to assign values straight to the target variables.

If you didn't use an intermediate to save it, you would be forced to overwrite data that you need:

String [j] = String [I];

String [I] = String [j];

See, in the second step you are just assigning whatever I is to itself, because you've overwritten whatever was there.

[gemera]

@alpo - compiler warnings?

[Alpo]

@alpo - compiler warnings?

Whoops, meant to write '\0'. Guess I don't haz the brain today lol.

I didn't actually write that on the spot, I was just remembering it from a few months ago. I'll fix it.

Edit: can't edit the original for some reason

#include <stdio.h>
#include <string.h>
int main(void)
{
    char String[] = "Ride The Snake!";
    int i = 0;
    int range = strlen(String) - 1;
    int j = range;
    for(; i < (range/2) || j > (range/2); i++, j--)
    {
        if(String[i] == '\0' || String[j] == '\0')
        {
            break;
        }
        else
        {
            char temp = String[j];
            String[j] = String[i];
            String[i] = temp;
        }
    }
    printf("%s\n", String);
    return 0;
}

[laserlight]

Dunno, this could well be an exercise in implementing a simple substitution cipher.

Alpo: great that you want to give implementing a string reversal program a try, but please do not spoonfeed. Besides, your loop looks too complicated: why check for a null character when you know that there won't be any? The range / 2 checks seem unnecessary too: you have two loop counters, so it is enough to terminate the loop when their values cross. If you were only using one loop counter then checking for half the range would make sense.

[Ilir Selmani]

Are you saying you need to reverse the string? Your explanation was very terse.

You might be able to reverse it using the general swap technique:

    char String[] = "Ride The Snake!";

    int i = 0;

    int range = strlen(String) - 1;

    for(int j = range; i < (range/2), j > (range/2); i++, j--)
    {
        if(String[i] == NULL || String[j] == NULL)
        {
            break;
        }
        else
        {
            char temp = String[j];

            String[j] = String[i];

            String[i] = temp;
        }
    }

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

Edit:

The swap technique basically goes like this. You take an intermediate variable of the correct type (temp), then assign it with one of the variables needing swapping ( String [j] ). Once this is done, you are free to assign values straight to the target variables.

If you didn't use an intermediate to save it, you would be forced to overwrite data that you need:

String [j] = String [I];

String [I] = String [j];

See, in the second step you are just assigning whatever I is to itself, because you've overwritten whatever was there.

Example:
char string[]=”ispit pia”; func (string);
after transformation: string[]=”rhkrg hrz”

I need to replace char--- 'a' with 'z'
'b' with 'y' ... first letter with last, second -- befor last...

i with r.. clear ?

[Matticus]

Your requirements are clear. What have you tried to solve this problem? Do you have any code written? Or at least some ideas on how to try solving it?

[Ilir Selmani]

Your requirements are clear. What have you tried to solve this problem? Do you have any code written? Or at least some ideas on how to try solving it?

I need some ideas ?

[Matticus]

I need some ideas ?

There's a lot more to programming than just writing code. Problem solving is an important skill to develop. That includes coming up with ideas on how to solve your problem. Sure we could give you some ideas, but that would rob you of a valuable learning experience.

So why don't you think about it for a bit and see what you come up with? Maybe sitting down with a pen and paper would help you visualize the problem and see potential solutions.

[rstanley]

Your instructor should have given you enough information especially in the last class to provide the solution. Did the instructor talk at all about using an array as a lookup table?

[Ilir Selmani]

I wrote this, idk that part of replacing.. with for or ?

insert

#include <stdio.h>
#define MAX 50
void changeString(char *str);
int main ()
{
char s[MAX];
 printf("Write string:\n");
 gets(s);
 changeString(s);
 printf("New string:\n");
 puts(s);
return 0;
}
void changeString(char *str)
{
int i = 0;
 while (str[i] != '\0')
{
    if(str[i]=='a')
    {
        str[i]='z';
    }
    if(str[i]=='b')
    {
        str[i]='y';
    }
    if(str[i]=='c')
    {
        str[i]='x';
    }


    i++;
}
str[i]='\0';
}

[Matticus]

While your idea seems technically valid at a glance, it is not very elegant. If that's sufficient to solve the problem, you could go with it, but rstanley gave a great hint that would make lead to much more concise code.

The "while()" loop would work as is, but a "for()" loop is the more natural selection when you are updating a variable each iteration of the loop.

Also, see here: FAQ > Why gets() is bad / Buffer Overflows - Cprogramming.com

[Alpo]

Dunno, this could well be an exercise in implementing a simple substitution cipher.

Alpo: great that you want to give implementing a string reversal program a try, but please do not spoonfeed. Besides, your loop looks too complicated: why check for a null character when you know that there won't be any? The range / 2 checks seem unnecessary too: you have two loop counters, so it is enough to terminate the loop when their values cross. If you were only using one loop counter then checking for half the range would make sense.

Sorry about the spoonfeeding. Thanks for the ideas as well, I didn't think about checking if they had crossed. I'll be thinking about how to do it with one loop counter .

[zub]

#include <stdio.h>


char* cipher_string(char* const str)
{
    char* s = str;
    int c;
    while( c = (unsigned char) *s ) {
        if( c > 64 && c < 91 ) {
            *s = 155 - c;
        } else if( c > 96 && c < 123 ) {
            *s = 219 - c;
        }
        ++s;
    }
    return str;
}


int main(void)
{
    puts(cipher_string("I say: \"Abracadabra\"!!!"));
    return 0;
}

[iMalc]

#include <stdio.h>


char* cipher_string(char* const str)
{
    char* s = str;
    int c;
    while( c = (unsigned char) *s ) {
        if( c > 64 && c < 91 ) {
            *s = 155 - c;
        } else if( c > 96 && c < 123 ) {
            *s = 219 - c;
        }
        ++s;
    }
    return str;
}


int main(void)
{
    puts(cipher_string("I say: \"Abracadabra\"!!!"));
    return 0;
}

No need for the nasty use of magic numbers there:

        if( c >= 'A' && c <= 'Z' ) {
            *s = 'A' + 'Z' - c;
        } else if( c >= 'a' && c <= 'z') {
            *s = 'a' + 'z' - c;
        }