check if string is number c

Checking if a String is a Number in C

To check if a string is a number in C, you can use the isdigit() function to check each character of the string. Here are the steps to do this:

1. Iterate Through the String: Loop through each character of the string.
2. Check if Each Character is a Digit: Use the isdigit() function to check if each character is a digit.
3. Handle Decimal Point: If the string represents a floating-point number, handle the decimal point separately.
4. Handle Negative Sign: If the string represents a negative number, handle the negative sign separately.

Here's a sample code snippet to demonstrate this:

#include <stdio.h>
#include <ctype.h>

int isNumber(const char* str) {
    int i = 0;
    int decimalPointCount = 0;
    if (str[0] == '-' || str[0] == '+') {
        i = 1;
    }
    for (; str[i] != '\0'; i++) {
        if (!isdigit(str[i])) {
            if (str[i] == '.' && decimalPointCount == 0) {
                decimalPointCount++;
            } else {
                return 0;
            }
        }
    }
    return 1;
}

int main() {
    const char* testString = "-123.45";
    if (isNumber(testString)) {
        printf("%s is a number.\n", testString);
    } else {
        printf("%s is not a number.\n", testString);
    }
    return 0;
}

In this code, the isNumber function checks each character of the input string to determine if it represents a valid number. It handles negative numbers and floating-point numbers as well.

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