Thread: How to scan string from user

Refer to what DRK told you in your topic switch case error in program: "The compiler tells exactly what the problem is - you provided some identifiers (red, green, blue) which were not previously declared."

This time, instead of red, green, blue, the identifiers are Ram, Dev, Devid. Again, an enum is a good choice, or you could use the other suggestions by Salem in post #4 of that topic.

Lookup strcmp function.

C library function - strcmp()

Tim S.

Originally Posted by laserlight

Refer to what DRK told you in your topic switch case error in program: "The compiler tells exactly what the problem is - you provided some identifiers (red, green, blue) which were not previously declared."

Look at this program

Code:

#include<stdio.h>
int main (void)
{
   unsigned int grade;
   printf("Promot user to enter grade of student : ");
   scanf("%d",&grade);
   
   if(grade > 100)
   {
     printf ("Entered invalid grade");
   }  
    else if (grade > 35)
   { 
    printf ("Your grade is %d \n You are passed",grade);  
   }
   else   
   {
     printf ("Your grade is %d \n You are failed",grade);
   }
 return 0;
}

Promot user to enter grade of student : 101
Entered invalid grade
Your grade is 45
You are passed
Your grade is 34
You are failed

if you compare first and second, both are similar the difference is only in scanning type.

In first example, I was trying to scan name while in second example I was trying to scan numbers.

When I scan numbers I don't need to use enum or define but when I need to scan string or name why I need to use enum or something like define red

Originally Posted by vead

When I scan numbers I don't need to use enum or define but when I need to scan string or name why I need to use enum or something like define red

It is not about the "scanning", it is about the identifiers. Consider this program:

Code:

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

int main(void)
{
    char name[10];
    printf("Enter your name: ");
    if (scanf("%9s", name) == 1)
    {
        if (strcmp(name, "vead") == 0)
        {
            printf("%s! Good to meet you.\n", name);
        }
        else
        {
            printf("%s is not vead.\n", name);
        }
    }
    else
    {
        printf("Error: could not read input.\n");
    }
    return 0;
}

In this case, I used a string literal "vead" for comparison with the input stored in the variable named name. Now try to compile this program:

Code:

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

int main(void)
{
    char name[10];
    printf("Enter your name: ");
    if (scanf("%9s", name) == 1)
    {
        if (strcmp(name, vead) == 0)
        {
            printf("%s! Good to meet you.\n", name);
        }
        else
        {
            printf("%s is not vead.\n", name);
        }
    }
    else
    {
        printf("Error: could not read input.\n");
    }
    return 0;
}

The only thing that changed is that instead of using the string literal "vead", I now use the identifier vead. You should get an error similiar to what you encountered previously. Now compile and run:

Code:

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

#define vead "vead"

int main(void)
{
    char name[10];
    printf("Enter your name: ");
    if (scanf("%9s", name) == 1)
    {
        if (strcmp(name, vead) == 0)
        {
            printf("%s! Good to meet you.\n", name);
        }
        else
        {
            printf("%s is not vead.\n", name);
        }
    }
    else
    {
        printf("Error: could not read input.\n");
    }
    return 0;
}

This is the same as the previous program, except that I added a #define to define the identifier named vead to be the string literal "vead". This is a macro, so during preprocessing the compiler (or preprocessor) would replace the identifier vead with the string literal "vead", thereby resulting in a program essentially identical to the first one.

Note that I misspoke about the use of enum: in this case you are dealing with strings, so enum is not applicable, but #define could be used, or you could use say, a const string. Notice that I used stahta01's suggestion for strcmp instead of comparing with == since == would compare pointers rather than the string content.

Originally Posted by vead

I prefer to write program without string.h library because every compiler has different library I am from electronics background

<string.h> is part of the C standard, so if it is not present, then it does imply that your environment significantly lacks standard library support, which is quite possible from your line of work. However, that also imply that you need to know your C well, so until you do, you should use the standard library.

Originally Posted by vead

How to write this program without strin.h library

Implement your own version of strcmp. This means you need to read up on strcmp, understand what it does and does not do. This also means you need to read up on C's concept of null terminated strings. If you expect to be spoonfed these, then you should discard your electronics background temporarily and just use the C standard library until you have more knowledge to be able to implement library functionality like this.