C cannot figure out if statement

Question

So I am trying to learn c however I can't figure out why this code won't run properly.

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

int main()
{
    char userName[25];
    char myName[25] = "myName";

    printf("Please enter your name: \n");
    scanf("%s", userName);

    if(userName == myName)
    {
        printf("Congratulations your name is myName!!!");
    }
    else
    {
        printf("Your name is %s how disappointing...", userName);
    }


    return 0;
}

The problem is that the if statement never seems to return true. Can anyone help me with this?

C lesson, char username[25] declares a pointer, char myName[25] declares a different pointer, pointing to two different locations in memory (on the stack in this case), therefore the pointers are never equal (the contents of each memory location may be equal, but the **memory** has to be compared, not the **pointers**) — Les, Jun 19 '15 at 19:48
regarding this line: 'scanf("%s", userName);' This call to scanf() allows the user to overrun the userName[] buffer. suggest: 'scanf("%24s", userName);' And check the returned value from scanf() (not the parameter values) to assure the operation was successful. — user3629249, Jun 19 '15 at 21:11
regarding this line: 'if(userName == myName)' This is comparing the addresses of the two strings, what you really want to do is compare the contents of the two strings. Suggest: 'if( !strcmp(userName, myName) )' — user3629249, Jun 19 '15 at 21:13

score 3 · Accepted Answer · answered Jun 19 '15 at 19:41

3

This line is comparing the locations of the strings, which are different, since you are comparing two different strings.

if(userName == myName)

The correct test in C is to use a library function.

#include <string.h>
...
if(strcmp(userName,myName) == 0)

answered Jun 19 '15 at 19:41

Weather Vane

33,872
7
36
56

Thank you I understand it now. – Meikk99 Jun 19 '15 at 19:45
@Meikk99, Weather Vane is right. Check all the answers given to your question and accept one (click on the tick icon at the left of the answer). Nice answer btw, +1. :) – gsamaras Jun 19 '15 at 19:47
alright will do thank you for the quick answer – Meikk99 Jun 19 '15 at 19:48

score 1 · Answer 2 · answered Jun 19 '15 at 19:38

1

In C, you should use strcmp() to compare two strings.

So change this:

if(userName == myName)

to this:

if(strcmp(userName,myName) == 0)

answered Jun 19 '15 at 19:38

gsamaras

71,951
46
188
305

score 1 · Answer 3 · answered Jun 19 '15 at 19:44

1

You cannot compare strings like that. What you are doing is comparing the pointers to the respective stings(which are obviously different). So,

 userName == myName

won't work here. You may use string functions to compare the two strings.

answered Jun 19 '15 at 19:44

Raman

2,735
1
26
46

score 0 · Answer 4 · answered Jun 19 '15 at 19:37

0

The statement if(userName == myName) will not work the way you are expecting it to. Use the strcmp() function to compare two strings.

answered Jun 19 '15 at 19:37

Alex Reynolds

95,983
54
240
345

score 0 · Answer 5 · answered Jun 19 '15 at 19:37

0

Use strcmp / strncmp declared in string.h to compare strings; in your program the values you are comparing (after conversion) are pointer values.

answered Jun 19 '15 at 19:37

ouah

142,963
15
272
331

C cannot figure out if statement

5 Answers5