Comparing user-inputted characters in C

Question

The following code snippets are from a C program   The user enters Y or N   char  answer     0    scanf     c   answer    if   answer      Y      y           do work   I can t figure out why this if statement doesn t evaluate to true   I checked for the y or n input with a printf and it is there  so I know I m getting the user input  Also when I replace the the condition of the if statement with 1  making it true   it evaluates properly

User · Accepted Answer

I see two problems   The pointer answer is a null pointer and you are trying to dereference it in scanf  this leads to undefined behavior    You don t need a char pointer here  You can just use a char variable as   char answer  scanf    c   amp answer     Next to see if the read character is  y  or  Y  you should do   if  answer     y     answer     Y          user entered y or Y      If you really need to use a char pointer you can do something like   char var  char  answer    amp var     make answer point to char variable var  scanf     c   answer   if   answer     y      answer     Y

User · Answer

answer shouldn t be a pointer  the intent is obviously to hold a character   scanf takes the address of this character  so it should be called as  char answer  scanf    c    amp answer     Next  your  or  statement is formed incorrectly   if  answer     Y     answer     y     What you wrote originally asks to compare answer with the result of  Y      y   which I m guessing isn t quite what you wanted to do

User · Answer

For a start  your answer variable should be of type char  not char    As for the if statement   if  answer      Y      y      This is first evaluating  Y      y  which  in Boolean logic  and for ASCII  is true since both of them are  true   non-zero   In other words  you d only get the if statement to fire if you d somehow entered CTRLA  again  for ASCII  and where a true values equates to 1  a   You could use the more correct   if   answer     Y       answer     y      but you really should be using   if  toupper answer      Y     since that s the more portable way to achieve the same end      a You may be wondering why I m putting in all sorts of conditionals for my statements  While the vast majority of C implementations use ASCII and certain known values  it s not necessarily mandated by the ISO standards  I know for a fact that at least one compiler still uses EBCDIC so I don t like making unwarranted assumptions

User · Answer

Because comparison doesn t work that way   Y      y  is a logical-or operator  it returns 1  true  if either of its arguments is true  Since  Y  and  y  are both true  you re comparing  answer with 1   What you want is if  answer     Y      answer     y   or perhaps   switch   answer      case  Y     case  y          Code for Y        break    default         Code for anything else

[c] Comparing user-inputted characters in C

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