CODEWITHSUNDEEP
cloopsswitch-statementscanf
Giovanni Luna
Giovanni Luna

Reputation: 25

switch statement creating infinite loop

I am writing a piece of code and in one part of my code I am using a switch statement in C language. if I press n it exits correctly if I press y it will infinite loop the default statement until I press control c. what am I doing wrong here. been changing the while statement but can't find the right one.

int main()
{
    char ans;
    printf("DO you want to continue?");
    scanf("%c", &ans);
    do
    {
      switch(ans)
      {
            case 'y':
                some stuff...
                   printf("DO you want to continue?");
                   scanf("%c", &ans);
                   break;
            case'n':
                  printf("BYE");
                  break;
            default:
                 printf("error, you must enter y or n");
                 continue;
       }
   }
   while (ans!='n');
   return 0;
}

Upvotes: 0

Views: 1641

Answers (1)

dreamlax
dreamlax

Reputation: 95325

When you press enter, the linefeed character \n is added to the input stream. Your code does not anticipate this, because switch(ans) only handles y, n or “everything else” (which includes the linefeed character).

To fix this, allow scanf to ignore any preceding whitespace by changing your format string to " %c" instead, e.g. 

scanf(" %c", &ans);
//     ^ space character inserted here

I think it would make more sense to move the scanf call to inside the loop, like this:

int main()
{
    char ans;

    do
    {
        printf("DO you want to continue?");
        if (scanf(" %c", &ans) != 1)
            break;

        switch(ans)
        {
            case 'y':
                //  some stuff...
                break;
            case 'n':
                printf("BYE");
                break;
            default:
                printf("error, you must enter y or n");
                continue;
        }
    }
    while (ans!='n');
}

Don't forget to always check the result of scanf(). It will return the number of items successfully scanned (in your case, you want it to return 1). If it returns 0 or a negative number, then another problem has occurred.

Upvotes: 1

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