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content/notes/ready/c-snippets.md

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+---
+title: C Snippets
+description: 
+date: 2025-02-17T08:56:33+00:00
+draft: false
+tags:
+  - c
+  - programming
+author: TrudeEH
+showToc: true
+---
+
+## Cast Strings to Numbers
+
+The `atoi()` function in `stdlib` is implemented similarly to the one below.  
+ 
+ASCII encodes numbers in order, after special characters. 
+
+The encoded value for `'0'` is 48, so subtracting any numeric char by 48 outputs its real numerical value.
+
+```C
+char number = '7';
+int result = number - 48;
+int same_result = number - '0';
+```
+
+Algorithm to convert strings to numbers:
+
+```C
+int str_to_int(char *str) {
+	int result = 0;
+	for (int i = 0; str[i] != '\0'; i++) {
+		if (str[i] < '0' && str[1] > '9') return -1; // Error if NaN
+		result = (result * 10) + (str[i] - '0');
+	return result;
+}
+```
+
+`(result * 10)` is shifting the previous number to the left, as it is an order of magnitude above the following digit.