Question

I have been looking all over for how to compare char elements in a char array correctly, but it is not working out for me. I am trying to compare the first char in a char array to an operator (checking to see if a + or -) exists.

EDIT: Saw my mistake. Logic error in the if statement. Thank you all for such quick responses.

At first I tried this:

    main(int argc, char *argv[]){

    int i;
    int len;
    char input[10];

    for(i = 1; i < 8; i++){

        len = strlen(argv[i]);
        strcpy(input,argv[i]);

        //debug purposes
        printf("%c\n",input[0]);

        if(input[0] != '+' || input[0] != '-')  {
            printf("incorrect number format. %s has no sign.\nnow terminating.\n", input);
        }// end if
    }//end for
}//end main

Then I read some more posts and saw that I should be comparing the chars using strcompare, so then I tried this: if( !strcmp(input[0],'+') || !strcmp(input[0],'-') )

However, they still don’t seem to be comparing properly. I get a segmentation fault with the above code and with my previous code, it would print the operator, but still go into the if statement saying that the format was incorrect. I am still fairly new to C, so any advice or tips on how I can get these chars to compare correctly will be much appreciated. Thanks.

Answer 1

The logic in the original if condition is incorrect:

if(input[0] != '+' || input[0] != '-')

That will always be true: if '+'== input[0] the condition equates to false || true, and vice versa for '-' == input[0].

It should be:

if(input[0] != '+' && input[0] != '-')