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  • 1 Post By kappilrinesh

puts() function doesn't return string

This is a discussion on puts() function doesn't return string within the C Programming forums, part of the General Programming Boards category; This is a program for Playfair Cipher, but after the encrypt function, puts() function is not returning the encrypted text. ...

  1. #1
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    puts() function doesn't return string

    This is a program for Playfair Cipher, but after the encrypt function, puts() function is not returning the encrypted text.
    i would be glad if someone helped me out.
    The code is as follows:

    Code:
    #include<stdio.h>
    #include<conio.h>
    #include<string.h>
    
    #define MAX 100
    
    void encrypt(char square[5][5],char ptext[MAX],char ctext[MAX]);
    void fillsquare(char key[MAX/4],char square[5][5]);
    int clear_input_buffer(void);
    
    void main()
    {
    	char key[MAX/4],square[5][5],ptext[MAX],ctext[MAX];
    	int ch,i,j;
    	clrscr();
    
    	do
    	{
    		printf("\nPlayfair Cipher\n");
    		printf("---------------\n");
    		printf("1. Encryption\n");
    		printf("2. Decryption\n");
    
    		printf("\nEnter your choice: ");
    		scanf("%d",&ch);
    
    		printf("Enter the key: ");
    		clear_input_buffer();
    		gets(key);
    
    		fillsquare(key,square);
    		//for(i=0;i<5;i++) for(j=0;j<5;j++) printf("%c",square[i][j]);
    		switch(ch)
    		{
    			case 1:
    				printf("\nEnter the plaintext to be encrypted: \n");
    				clear_input_buffer();
    				gets(ptext);
    
    				printf("\nstart"); puts(ptext); printf("end");
    				encrypt(square,ptext,ctext);
    
    				printf("\nCiphertext: \n");
    
    				break;
    
    			case 2:
    
    				break;
    
    			default:
    
    				break;
    		}
    
    	}
    	while(ch=='y' || ch=='Y');
    	getch();
    }
    
    int clear_input_buffer(void)
    {
    	int ch;
    	while(((ch=getchar())!=EOF) && (ch != '\n'));
    	return ch;
    }
    
    void fillsquare(char key[MAX/4],char square[5][5])
    {
    	int i,j,l=strlen(key),y=0,x,count;
    	char alpha=97;
    	for(i=0;i<5;i++)
    	{
    		for(j=0;j<5;j++)
    		{
    			if(y<l)
    			{
    				square[i][j]=key[y++];
    				//printf("%c",square[i][j]);
    			}
    			else
    			{
    				count=1;
    				while(count==1)
    				{
    					x=0,count=0;
    					while(key[x]!='\0')
    					{
    						if(key[x++]==alpha)
    						{
    							count++;
    							alpha++;
    						}
    					}
    
    				}
    				square[i][j]=alpha++;
    			}
    		}
    	}
    }
    
    void encrypt(char square[5][5],char ptext[MAX],char ctext[MAX])
    {
    	int x=0,y=0,i,j,al1row,al1col,al2row,al2col;
    
    	printf("\nout of while");
    	while(ptext[x]!='\0')
    	{
    
    		printf("\nwhile");
    		if(ptext[x]==ptext[x+1])
    		{
    
    		}
    		else
    		{
    			for(i=0;i<5;i++)
    			{
    				for(j=0;j<5;j++)
    				{
    					if(ptext[x]==square[i][j])
    					{
    						al1row=i;
    						al1col=j;
    					}
    					if(ptext[x+1]==square[i][j])
    					{
    						al2row=i;
    						al2col=j;
    					}
    				}
    			}
    			printf("\nal1row: %d al1col: %d al2row: %d al2col: %d",al1row,al1col,al2row,al2col);
    			if(al1row==al2row)
    			{
    				ctext[y++]=square[al1row][al1col+1];
    				ctext[y++]=square[al2row][al2col+1];
    			}
    			if(al1col==al2col)
    			{
    				ctext[y++]=square[al1row+1][al1col];
    				ctext[y++]=square[al2row+1][al2col];
    			}
    			if(al1row != al2row && al1col!=al2col)
    			{
    				ctext[y++]=square[al2row][al1col];
    				ctext[y++]=square[al1row][al2col];
    			}
    			x+=2;
    		}
    		ctext[y]='\0';
    	}
    }
    Last edited by kappilrinesh; 02-04-2012 at 12:25 AM.
    stahta01 likes this.

  2. #2
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    puts() is not being called after doing the encryption, so you can hardly expect it to output the encrypted text.

    Also, main() returns int not void, and gets() is a recipe for a buffer overrun.
    Right 98% of the time, and don't care about the other 3%.

  3. #3
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    yeah, my mistake.
    but there is a puts() function before the encrypt function and it is not returnin the ptext string on the screen.

  4. #4
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    Have you considered the possibility that your call of clear_input_buffer() is discarding the input?
    Right 98% of the time, and don't care about the other 3%.

  5. #5
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    its working now. i removed the call to the function clear_input_buffer().

    thank you

  6. #6
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    Now, can you explain why that worked? I ask that because, in the process of working out the answer, you will gain some insights into how functions like gets() and getchar() work and, more importantly, how they interact when you use them together..

    You might also want to consider using fgets() (note the leading 'f') rather than gets(). Consider what will happen in your code if the user enters 200 characters without an intervening newline.
    Right 98% of the time, and don't care about the other 3%.

  7. #7
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    Hints to get the code to work as I thought it should.
    Playfair Cipher does not normally use "J" letter instead it is replaced with "I".
    Therefore the 5x5 matrix should not have J in it.

    Note: The other logic problem is left for user to fix. Hint in body of "if(al1row != al2row && al1col!=al2col)"

    Tim S.
    "Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the universe trying to produce bigger and better idiots. So far, the Universe is winning." Rick Cook

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