Loop does not recognize string of char in C

Question

I am writing a code and I need to use a loop. I am reading data from a file (data.txt) that looks like this:

IMPORT 450

EXPORT 200

IMPORT 100

and so on.

Here is the segment of the code that I am having trouble with

inputfile = fopen("c:\\class\\data.txt","r");
fscanf(inputfile,"%s %f", &transaction, &amount);

do{                 
     total += amount;             
     printf("Data %s  %f   %f\n", transaction, amount, total);
     fscanf(inputfile, "%s", &transaction);

}while (transaction == "IMPORT" || transaction == "EXPORT");

When I add a printf line to check what 'transaction' is it shows IMPORT, so I am not sure why the do-while loop is not repeating.

Thank you!

simonc · Accepted Answer · 2013-05-05 19:17:35Z

4

Assuming transaction is a char array, the comparison

transaction == "IMPORT"

will compare the address of transaction against the address of the string literal "IMPORT".

You need to use

while (strcmp(transaction, "IMPORT") == 0 ||
       strcmp(transaction, "EXPORT") == 0)

to compare strings in C.

answered May 5, 2013 at 19:17

simonc

42.3k12 gold badges91 silver badges105 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

leander · Accepted Answer · 2013-05-05 19:18:16Z

1

What type is transaction?

In order to use it with fscanf's %s operator it probably is char[], and in that case you need to use strcmp; the == operator will compare character pointer addresses, rather than contents.

answered May 5, 2013 at 19:18

leander

8,7471 gold badge32 silver badges43 bronze badges

Comments

schaeferpp · Accepted Answer · 2013-05-05 19:22:51Z

0

When you try to check transaction == "IMPORT" C only compares the pointer of the first char. That doenst work really well. Maybe try this code:

int str_equal(char* str1, char* str2)
{
    int i, len;

    if ((len = strlen(str1)) != strlen(str2))
    {
        return 0;
    }

    for (i = 0; i < len; i++)
    {
        if (toupper(str1[i]) != toupper(str2[i]))
    {
            return 0;
        }
    }

    return 1;
}

answered May 5, 2013 at 19:22

schaeferpp

11910 bronze badges

Comments

BLUEPIXY · Accepted Answer · 2013-05-05 19:44:30Z

0

probably like this

    while(2==fscanf(inputfile,"%s %f", transaction, &amount)){
        if(strcmp("IMPORT", transaction)==0)
            total += amount;
        else if(strcmp("EXPORT", transaction)==0)
            total -= amount;
        else
            break;
        printf("Data %s  %f   %f\n", transaction, amount, total);
    }

answered May 5, 2013 at 19:44

BLUEPIXY

40.2k7 gold badges37 silver badges73 bronze badges

Collectives™ on Stack Overflow

Loop does not recognize string of char in C

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related