Is there a way to create a gender evaluation

Question

I'm trying to get the user of a C program to Enter M for Male and F for Female and to loop through if it doesn't meet M or F . Below I have tried the following code but it loops twice giving the correct answer. For instance after entering M it loops and prints

FALSE gender .. please enter M for Male and M for Female

is there any way to solve it .

The goal is if the user enter M or F it will work without needing to enter it a second time.
if anything else it may ask a number of times

 #include "Gender.h"
 #include<stdio.h>


  char sex;
  void Gender(){

  printf("\nEnter Student Gender ('example M for Male  F for Female):\n");

  scanf(" %s",&sex);



      while (sex != "M" || sex != "M"){
       printf ("\n FALSE gender .. please enter M for Male and M for Female:\n");
        scanf(" %s",&sex);
        printf("\nStudent Sex :%c", sex,"\n");
        return;
      }


  }

The expression in the `while` statement is checking `"M"` twice. Also, to compare strings in C, use the `strcmp` function. — user3386109, Apr 23 '19 at 23:09
`"%s"` consumes leading whitespace, so the space in `" %s"` is not needed -- HOWEVER, you do not check the return (ignoring a manual `EOF`) and you fail to remove any extraneous characters beyond the first character (e.g. after reading `sex`, `int c = getchar(); while (c != '\n' && c != EOF) c = getchar();`) This beyond your mismatch in types between `char sex` and `"%s"` expecting a pointer to char with sufficient storage to hold the string (including the *nul-terminating* character) — David C. Rankin, Apr 23 '19 at 23:13
**M** for Male and **M** for Female (inside the loop)? I think the ladies are entitled to feel annoyed. The `return` inside the loop means that people get one retry, which isn't tested. You also throw away the result of the user's input — that's not very good. Surely you should return the selected gender? It might be worth adding a count on the retries and stopping people from going into a loop. Stop after 10 failed attempts, for example. — Jonathan Leffler, Apr 23 '19 at 23:23
@JonathanLeffler I now realize my typo but still when i change the F for female it still does the same thing. — Angelo, Apr 24 '19 at 01:53

score 5 · Answer 1 · answered Apr 23 '19 at 23:12

sex is a single char variable, but you are treating it as a pointer to a string.

Change your scanf call to have %c (single character) in the format string, rather than %s.
Change your tests for the value of sex to use single quotes (i.e. if (sex == 'M')).

Note that though this code should not need string comparison if the variable sex is treated like the single char it is, if you were to compare strings in a future project, you would not use the operators == and != - instead, use the function strcmp in <string.h>

Should point out when the user does enter something that is not M or F then you should read up to the new line character and dispose of that data in the stream — Ed Heal, Apr 24 '19 at 01:22

ChuckCottrill · Answer 2 · 2019-04-24T04:01:35.363

Several things, I've provided an implementation with comments...

Include ctype.h to use toupper(3) and allow both upper and lower case entry. You can either use character comparison, or string comparison, I gave you both, pick one.

#include "Gender.h"
#include <stdio.h>

//you should really define these in your Gender.h file...
#define MALE "M"
#define FEMALE "F"
//you should really define these in your Gender.h file...
static const char* GenderAllowed = MALE" for Male and "FEMALE" for Female";
static const char* GenderPrompt = "Enter Student Gender";

//compare as string[1] - keep either this
#include <string.h>
int sexValidc( char* sex ) {
    return ( (0==strncmp(sex,MALE,1)) || (0==strncmp(sex,FEMALE,1)) );
}

//compare only first character - or keep this
#include <ctype.h>
int sexValids( char* sex ) {
    char sexch = toupper(*sex); //fold first character to upper case
    return ( (*MALE==sexch) || (*FEMALE==sexch) );
}

char Gender() {
    char sex[69+1]; //since you wanted to use %s, need a buffer, your &char allows stack overflow & wild memory pointer-ing
    printf("\n%s (%s):\n",GenderPrompt,GenderAllowed); //DRY - Dont Repeat Yourself...
    int done = 0;
    while( !done ) {
        scanf(" %69s",sex); //avoid stackoverflow :-)
        if( !sexValidc( sex ) ) {
//printf("blech, entered: %s\n",sex); //debugging, remove when comfortable
            printf("\n FALSE gender .. %s %s:\n",GenderPrompt,GenderAllowed);
        }
        else { //valid
            done = 1;
        }
    }
    printf("\nStudent Sex :%c\n", *sex);
    return *sex; //once you enter valid value, return it...
}

int main() {
    Gender();
}

Also read this about automatic allocation of buffer space, difference between %ms and %s scanf

I am trying it this way char sex; void Gender(){ printf("\nEnter Student Gender (example M for Male F for Female):\n"); scanf(" %c",&sex); switch(sex){ case 'M': case 'm': printf("Student Sex : Male"); break; case 'F': case 'f': printf("Student Sex : Female"); break; default: printf("\n FALSE gender .. please enter M for Male and F for Female:\n"); } } — Angelo, Apr 24 '19 at 02:50
You gotta use only one of the sexValid functions - I've changed the names to end in 'c' and 's', and guessed which you want... — ChuckCottrill, Apr 24 '19 at 04:00

Is there a way to create a gender evaluation

2 Answers2