Strcat(a[1],"22") how to use? C programming

Question

i'm trying to make a program that if the previous letter is the same with the current letter that will be outputed will put a space between them...

#include<stdio.h>
#include<string.h>
#include<ctype.h>
#define T 100
#define S 255

int main(){
char Arrayinput[T][S];
char Arrayoutput[T][S*5];
int i, c, x;
for(i=0;i<T;i++){
    for(c=0;c<S*5;c++){
        Arrayoutput[i][c]=0;
    }
}
scanf("%d", &x);
getchar();
for(i=0;i<x;i++){
        gets(Arrayinput[i]);
}
for(i=0;i<x;i++){
    for(c=0;c<strlen(Arrayinput[i]);c++){
            switch(toupper(Arrayinput[i][c])){
            case 'A':
                if(Arrayoutput[i][c-1]=='2')
                    strcat(Arrayoutput[i]," ");
                strcat(Arrayoutput[i],"2"); break;
            case 'B':
                if(Arrayoutput[i][c-1]=='2')
                    strcat(Arrayoutput[i]," ");
                strcat(Arrayoutput[i],"22"); break;
            case 'C':
                if(Arrayoutput[i][c-1]=='2')
                    strcat(Arrayoutput[i]," ");
                strcat(Arrayoutput[i],"222"); break;
}    }    }

for(i=0;i<x;i++){
    printf("case #%d:%s\n",i+1,Arrayoutput[i]);
}

system("pause");
return 0;

for some case..

if i input.. bca it out puts 22 222 2 which is correct.. such as cab = 222 22 2 bac = 22 2 222

but when ever i input abc it out puts... 2 22222... i dont know why... pls help?

also i made all the arrayoutput[][]'s elemet to 0 so there will be no garbage data inside them. — HerlDerp, Jan 30 '15 at 14:56
Please edit your question to include the declarations of `ArrayInput` and `ArrayOutput`, as well as how you initialize them. — Some programmer dude, Jan 30 '15 at 14:59
Post an [MCVE](http://stackoverflow.com/help/mcve). If there is something you do *not* understand regarding how [**strcat()**](http://en.cppreference.com/w/c/string/byte/strcat) works from its documentation, you may want to include that in your question as well. — WhozCraig, Jan 30 '15 at 15:00
`Arrayoutput[i][c-1] --> Arrayoutput[0][-1] for c=0` are you aware of this? — Gopi, Jan 30 '15 at 15:01
Also, learn to use a debugger, then you can step through the code line by line to help yourself find the problem. — Some programmer dude, Jan 30 '15 at 15:01
Probably because of UB. When `c` is 0, `c-1` will result in -1. — Spikatrix, Jan 30 '15 at 15:01
First of all the first loop all checks `if(Arrayoutput[i][c-1]=='2')` evaluate a -1 position of array, means undefined behaviour. — LPs, Jan 30 '15 at 15:05
im aware of -1, but why the heck the bca cba or any other order works fine just abc doesn't work as it is? — HerlDerp, Jan 30 '15 at 15:07
No. Its UB meaning that anything can happen. For example, division by zero is undefined meaning that the results are unpredictable. — Spikatrix, Jan 30 '15 at 15:14

LPs · Answer 1 · 2015-01-30T16:05:03.683

0

Simply because of the if(Arrayoutput[i][c-1]=='2') of 'C' case with input abc will check always c-1 position, that is always " ".

case A -> "2"
case B -> "2 22"
case C -> Arrayoutput[i][c-1] is Arrayoutput[i][1] that is a space then no space added at the end of the string.

Try this

#include<stdio.h>
#include<string.h>
#include<ctype.h>
#define T 100
#define S 255

int main(){
char Arrayinput[T][S];
char Arrayoutput[T][S*5];
int i, c, x;
int len;
for(i=0;i<T;i++){
    for(c=0;c<S*5;c++){
        Arrayoutput[i][c]=0;
    }
}
scanf("%d", &x);
getchar();
for(i=0;i<x;i++){
        gets(Arrayinput[i]);
}
for(i=0;i<x;i++){
    for(c=0;c<strlen(Arrayinput[i]);c++){
        len = strlen(Arrayoutput[i]);
            switch(toupper(Arrayinput[i][c])){
            case 'A':
                if((len != 0) && (Arrayoutput[i][len-1]=='2'))
                    strcat(Arrayoutput[i]," ");
                strcat(Arrayoutput[i],"2"); break;
            case 'B':
                if((len != 0) && (Arrayoutput[i][len-1]=='2'))
                    strcat(Arrayoutput[i]," ");
                strcat(Arrayoutput[i],"22"); break;
            case 'C':
                if((len != 0) && (Arrayoutput[i][len-1]=='2'))
                    strcat(Arrayoutput[i]," ");
                strcat(Arrayoutput[i],"222"); break;
}    }    }

for(i=0;i<x;i++){
    printf("case #%d:%s\n",i+1,Arrayoutput[i]);
}

return 0;
}

OUTPUT

enter image description here

edited Jan 30 '15 at 16:05

answered Jan 30 '15 at 15:18

LPs

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have you tried the code? because... it really does ticks me.. abc should be = 2 22 222 but print outs 2 22222 and others prints fine.. why is that thats all, serously.. yes it wont put if its not '2' but why doesn't it go through abc=2 22222 as it should be what i want it be? – HerlDerp Jan 30 '15 at 15:24
The posted code works as you need. abc = 2 22 222. Compiled gcc 4.7.2 on Debian – LPs Jan 30 '15 at 15:29
I edited my answer. You have to think step by step. As edited the third check cheks the second char of the string that is "2 22". Then the if in case 'C' evaluets the space that is not == '2', the no space added at the string before to add "222" – LPs Jan 30 '15 at 15:59
i did found an alternative way.. though.. just printing them immedately. – HerlDerp Jan 31 '15 at 04:34
Your question was about to explain you why your code was not working. I did it, and corrected your code. To have the same output with a different algoritm is another story, because of your code has 1000k of wrong things... – LPs Jan 31 '15 at 07:52

Strcat(a[1],"22") how to use? C programming

1 Answers1