CODEWITHSUNDEEP
c
Yvonne95
Yvonne95

Reputation: 13

C -- How to take care of sensitive input in C program?

I'm trying to write a program to deal with user input in C. I have to ensure the program accept the input by user like taking "y", "yep", "yeah" as "yes" in my program for later use (i.e. need to use strcmp(xx,"yes") == 0). I have handled the mixed case character.

So how can I write a function to summerize "y", "yeah", "yep" and make them equal to "yes" after all??

if ((strcmp(letter , "y") == 0) || ......)

return "yes";

.......

Plus, if the program asks users to enter a question for some purposes, is it possible to add a question mark (?) for users if users forget to add one?

Upvotes: 0

Views: 102

Answers (2)

Michi
Michi

Reputation: 5297

There is a function named strncasecmp which is not present on all Systems (I'm a Linux User), because is not a standard function:

int strncasecmp(const char *s1, const char *s2, size_t n);

The function looks like this if is not present on your System:

int strncasecmp(char *s1, char *s2, size_t n){
    if (n == 0){
        return 0;
    }

    while (n-- != 0 && tolower(*s1) == tolower(*s2)){
        if (n == 0 || *s1 == '\0' || *s2 == '\0'){
            break;
        }
        s1++;
        s2++;
    }

    return tolower(*(unsigned char *) s1) - tolower(*(unsigned char *) s2);
}

Which you can use it like this:

#include <stdio.h>
#include <strings.h>

int main(void){
    char *user_input = "yes";
    char *ch = "Y";

    if (strncasecmp(user_input, ch, 1) == 0){
        printf("True\n");
    }else{
        printf("False\n");
    }

    return 0;
}

As you can see there is no problem with case sensitive. The strncasecmp function is found in strings.h and not in string.h

is it possible to add a question mark (?) for users if users forget to add one?

Yes, you can. The following piece of code is a way to help you to understand how to do it:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main(void){
    char *question = "What is your Question";
    size_t length = strlen(question);
    char *addQuestion = malloc(length + 2);

    memcpy(addQuestion,question,length + 1);
    printf("Before\n%s\n",addQuestion);

    strcat(addQuestion, "?");

    printf("\n");
    printf("After\n%s\n",addQuestion);
    free(addQuestion);
    return 0;
}

Output:

Before
What is your Question

After
What is your Question?

Upvotes: 0

SwedishOwlSerpent
SwedishOwlSerpent

Reputation: 355

Just compare the first letter with 'y'. For example, if you save the user input in a variable called user_input:

if ((user_input[0] == 'y') || ...)

And as for your second question, you can add that option, for example (it validates the input length before adding the "?", thanks to Vane for the correction):

if ((input_length > 0) && (user_input[input_length-1] != '?')) {
    strcat(user_input, "?");
}

Upvotes: 1

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