Check if User Inputs a Letter or Number in C

Question

Is there an easy way to call a C script to see if the user inputs a letter from the English alphabet? I\'m thinking something like this:

if (variable == a -          


        

Answer 1

isalpha() will test one character at a time. If the user input a number like 23A4, then you want to test every letter. You can use this:

bool isNumber(char *input) {
    for (i = 0; input[i] != '\0'; i++)
        if (isalpha(input[i]))
            return false;
    return true;
}

// accept and check
scanf("%s", input);  // where input is a pointer to a char with memory allocated
if (isNumber(input)) {
    number = atoi(input);
    // rest of the code
}

I agree that atoi() is not thread safe and a deprecated function. You can write another simple function in place of that.