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if problem

This is a discussion on if problem within the C Programming forums, part of the General Programming Boards category; Problem is when i press B as the center element the line at the end "if(centerelement=="B") should run what inside. ...

  1. #1
    Registered User
    Join Date
    Sep 2011
    Posts
    117

    if problem

    Problem is when i press B as the center element the line at the end "if(centerelement=="B") should run what inside.

    I put this inside the if statement:
    Code:
    VEC = 3;
    printf("%d",VEC);
    I put the printf so i can verify that the value of VEC is now 3.

    Here is the source code:

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    
    int main()
    {
    	char charselect[1];
    	int select;
    
    	char tempelement[3];
    
    	char centerelement[3];
    	char pelement1[3]; //periferal element 1
    	char pelement2[3]; //periferal element 2
    	char pelement3[3]; //periferal element 3
    	char pelement4[3]; //periferal element 4
    
    	int totalVE; //total valance electrons
    
    	int VEC; //# of valance electrons in center
    	int VE1;
    	int VE2;
    	int VE3;
    	int VE4;
    	
    /*	H = 1;
    	B = 3;
    	C = 4;
    	N = 5;
    	P = 5;
    	O = 6;
    	S = 6;
    	Se = 6;
    	F = 7;
    	Cl = 7;
    	Br = 7;
    	I = 7;
    */
    
    
    
    	printf("What is the structure of the Lewis Structure?\n\n");
    	printf("1 - Tetrahedral\n\n");
    	printf("Input corresponding number: ");
    	gets (charselect);
    	select = atoi(charselect);
    
    	if (select == 1)
    	{
    		printf("You selected Tetrahedral.\n\n");
    		printf("What is the center Element? \n");
    		scanf("%s",centerelement);
    		printf("What is the 1st periferal element? \n");
    		scanf("%s",pelement1);
    		printf("What is the 2nd periferal element? \n");
    		scanf("%s",pelement2);
    		printf("What is the 3rd periferal element? \n");
    		scanf("%s",pelement3);
    		printf("What is the 4th periferal element? \n");
    		scanf("%s",pelement4);
    
    		if(centerelement=="B")
    		{
    			VEC = 3;
    			printf("%d",VEC);
    		}
    
    		printf("%s %s %s %s %s", centerelement, pelement1, pelement1, pelement1, pelement1);
    	}
    }

  2. #2
    Registered User
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    Long Beach, CA
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    5,444
    You can't compare strings with the == operator. Try using strcmp. It returns 0 when the strings are identical.

  3. #3
    Registered User
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    117
    Code:
    Ah, this is what I get for reading only half of the book, being impatient/excited to try out something by myself...
    
    I put:
    
    Code:
    int strcmp(centerelement,"B");
    But getting an error, what is wrong with what I put? I did "#include <string.h>" on top.
    Nevermind, The example given was bad. I removed int from strcmp and put in "int compare;" then "compare = strcmp(centerelement,"B");"

    Fixed it, thanks
    Last edited by JonathanS; 09-01-2011 at 08:41 AM.

  4. #4
    Banned
    Join Date
    Aug 2010
    Location
    Ontario Canada
    Posts
    9,547
    No need for an intermediate variable, you can just do this...
    Code:
    //  old way... if(centerelement=="B")
    
    if (! strcmp(centerelement, "B"))
         {
           VEC = 3;
           printf("%d",VEC);
         }
    I generally advise that you always look for ways to simplify your code, never using anything that's not entirely necessary to get the job done...
    Last edited by CommonTater; 09-01-2011 at 10:06 AM.

  5. #5
    a_capitalist_story
    Join Date
    Dec 2007
    Posts
    2,648
    First off...stop using gets()! It's insecure; view the FAQ here for why and how to fix it.

    Secondly, make charselect a single char variable, rather than an array of length 1 (which is wrong, because then there's no room for the required null terminator).

    Example code:

    Code:
    #include <stdio.h>
    
    int main(void)
    {
       char selection;
       int c = 0;
       printf("1 - Tetrahedral\n");
       printf("Select one: ");
       while (scanf("%c", &selection) != 1) {
          while((c = getchar()) != '\n') ; /* Consume any leftover chars in the buffer */
          printf("Invalid selection!\nSelect one: ");
       }
       while((c = getchar()) != '\n') ; /* Consume any leftover chars in the buffer */
       if (selection == '1') {
          printf("You selected %c\n", selection);
       } else {
          printf("You selected %c, which is invalid!\n", selection);
       }
       return 0;
    }
    CommonTater likes this.

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