CODEWITHSUNDEEP
c
user5412127
user5412127

Reputation:

How to compare if a char* is greater than or equal to another string/number?

I'm using scanf to input numbers and +,-,/ operators into a stack.

int scan = 1;
char * p = malloc(sizeof(char)*5);
while (scan = 1) {
    scanf("%1s", p);
    if(p>='0' && p<='9'){
        push(stack, p);
        print(stack);
    }
}

Why does it never meet the condition? How can you compare strings?

Upvotes: 0

Views: 1324

Answers (2)

John3136
John3136

Reputation: 29266

if(p>='0' && p<='9'){

p is a char*, '0' is a char. Your compiler should have warned you about comparing incompatible types. Use *p instead (same applies to '9' obviously). In my head *p gets read as "contents of p" (in this context)

In the more general case, use strcmp() to compare strings.

If your compiler did warn you about the bad compare: take it on board, most compiler warnings should be listened to and not ignored. If your compiler didn't warn you look up how to enable all the warnings.

Upvotes: 1

Dave Costa
Dave Costa

Reputation: 48121

Well, if what you want to do is test whether the first character of the string is between '0' and '9', you should do:

(*p >= '0' && *p <= '9')

But if you want to compare strings as strings, the old school C library function for that is strcmp. I'm sure these days there are lots of other libraries that may offer more functionality.

Upvotes: 2

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