comparing 2 strings with pointer

This is a discussion on comparing 2 strings with pointer within the C Programming forums, part of the General Programming Boards category; Hello all, I am trying to make a program that compares two strings, but I got stuck here I am ...

  1. #1
    Registered User meriororen's Avatar
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    comparing 2 strings with pointer

    Hello all,

    I am trying to make a program that compares two strings, but I got stuck here
    I am a newbie in using pointer, can anyone help?

    here is the source code :

    Code:
    #include <stdio.h>
    
    int str_equal(const char *s1, const char *s2){
    	while(*s1 != '\0' && *s2 != '\0'){
    		if(*s1 != *s2){return 0;}
    		else{*s1++;*s2++;}
    	}
    	return 1;
    }
    
    
    int main(void){
    	char p, q;
    	
    	printf("Input a string : ");
    	scanf("%s",&p);
    	printf("Input another string : ");
    	scanf("%s",&q);
    	
    	if(str_equal(&p, &q)){
    		printf("The strings are the same.\n");
    	}else{
    		printf("The strings are not the same.\n");
    	}
    
    	return 0;
    }
    thanks in advance.

  2. #2
    Kernel hacker
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    So exactly what is NOT working in your code?

    I suspect it may be that char p and q are only able to hold a single character. That can ONLY work if you have an empty string... For all other strings, you need a char array.

    When you pass an array, it turns into a pointer, so you don't need th &.

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  3. #3
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    Hi,
    Do you want to compare Char (s) or Strings ?

  4. #4
    ATH0 quzah's Avatar
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    Code:
    char p, q;
    	
    printf("Input a string : ");
    scanf("%s",&p);
    printf("Input another string : ");
    scanf("%s",&q);
    Specifically, that. Those cannot be strings, unless you want your "string" to only be the null character. That's the only way you can consider a single character a string.


    Quzah.
    Hope is the first step on the road to disappointment.

  5. #5
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    If you want to compare strings ,in your main function you first need to be sure that those strings are well taken from user.

    i recommend you to define a maximum size for your strings, and use fgets to read string from standard input. you can better control what user gives.

    using 2 pointers on those string you can use you function to compare them.

  6. #6
    Registered User meriororen's Avatar
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    actually it always returns 0 when I input more than one character..

    I tried to do this

    Code:
    char p[10], q[10];
    to determine the length of the array, but it got stuck in compiling process. It says "[Warning] passing arg 1 of `str_equal' from incompatible pointer type " and also in the second arg.

  7. #7
    Kernel hacker
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    Yes, remove the & on the call to str_equal [and scanf].

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  8. #8
    DESTINY BEN10's Avatar
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    Quote Originally Posted by meriororen View Post
    Hello all,

    I am trying to make a program that compares two strings, but I got stuck here
    I am a newbie in using pointer, can anyone help?

    here is the source code :

    Code:
    #include <stdio.h>
    
    int str_equal(const char *s1, const char *s2){
    	while(*s1 != '\0' && *s2 != '\0'){
    		if(*s1 != *s2){return 0;}
    		else{*s1++;*s2++;}
    	}
    	return 1;
    }
    
    
    int main(void){
    	char p[10], q[10];
    	
    	printf("Input a string : ");
    	scanf("%s",p);
    	printf("Input another string : ");
    	scanf("%s",q);
    	
    	if(str_equal(&p, &q)){
    		printf("The strings are the same.\n");
    	}else{
    		printf("The strings are not the same.\n");
    	}
    
    	return 0;
    }
    thanks in advance.
    You should do this.
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  9. #9
    ATH0 quzah's Avatar
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    Your string function is actually a sort of strstr, not a strcmp function. Except for what it returns. But it functions more like strstr. At the end, if one string has reached the end, but not the other, it's still going to return 1.

    Quzah.
    Hope is the first step on the road to disappointment.

  10. #10
    Registered User meriororen's Avatar
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    woops, I did it. I tried removing & and having a little change on the function.

    thanks all

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