Data Validation for the number of arguments not changing value-CodePudding

I have this code that needs to take in 3 command line arguments that are numbers in order to convert from Fahrenheit to Celsius. I have everything working in the program but I am having issues with changing the 'step' variable to int 1 if it is not specified as an argument when running the program. I added the if statement to check if the argument exists and then have that change the value to one if it does not but it returns a segmentation fault. Here is the if statement:

int step = atoi(argv[3]);

        if(argc == 2){

                step = 1;

        return step;
        }

Here are the results of running the program:

root@computer:/home/sus/cyb126/homework$./temperature_chart 32 212
Segmentation fault (core dumped)
root@computer:/home/sus/cyb126/homework$./temperature_chart 32 212 20
32    0.000000
52    11.111111
72    22.222221
92    33.333332
112   44.444443
132   55.555557
152   66.666664
172   77.777779
192   88.888885
212   100.000000

I don't understand why it returns a segmentation fault by compiles fine with no warnings. I can only think that it does not listen to the if statement for some reason.

Appreciate any help.

Changed code to the following after I was answered with good advice below:

int step;

        if  (argc == 2) {
        step = atoi(argv[3]);
        }
        else {
        step = 1;
        }

CodePudding user response：

When you pass 2 arguments the argv array is only 3 elements long ( the number of elements is always argc 1). This means that by accessing argv[3] you are accessing the fourth element of a three element vector. This is an out of bound access and you get a seg fault.