Add Octal to Decimal Conversion (TheAlgorithms#605)

Author: cyrixninja

DIRECTORY.md

@@ -45,6 +45,7 @@
     * [Decimal to Binary](https://github.com/TheAlgorithms/Rust/blob/master/src/conversions/decimal_to_binary.rs)
     * [Hexadecimal to Binary](https://github.com/TheAlgorithms/Rust/blob/master/src/conversions/hexadecimal_to_binary.rs)
     * [Octal to Binary](https://github.com/TheAlgorithms/Rust/blob/master/src/conversions/octal_to_binary.rs)
+    * [Octal to Decimal](https://github.com/TheAlgorithms/Rust/blob/master/src/conversions/octal_to_decimal.rs)
   * Data Structures
     * [Avl Tree](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/avl_tree.rs)
     * [B Tree](https://github.com/TheAlgorithms/Rust/blob/master/src/data_structures/b_tree.rs)

src/conversions/mod.rs

@@ -3,8 +3,10 @@ mod binary_to_hexadecimal;
 mod decimal_to_binary;
 mod hexadecimal_to_binary;
 mod octal_to_binary;
+mod octal_to_decimal;
 pub use self::binary_to_decimal::binary_to_decimal;
 pub use self::binary_to_hexadecimal::binary_to_hexadecimal;
 pub use self::decimal_to_binary::decimal_to_binary;
 pub use self::hexadecimal_to_binary::hexadecimal_to_binary;
 pub use self::octal_to_binary::octal_to_binary;
+pub use self::octal_to_decimal::octal_to_decimal;

src/conversions/octal_to_decimal.rs

@@ -0,0 +1,60 @@
+// Author: cyrixninja
+// Octal to Decimal Converter: Converts Octal to Decimal
+// Wikipedia References:
+// 1. https://en.wikipedia.org/wiki/Octal
+// 2. https://en.wikipedia.org/wiki/Decimal
+
+pub fn octal_to_decimal(octal_str: &str) -> Result<u64, &'static str> {
+    let octal_str = octal_str.trim();
+
+    if octal_str.is_empty() {
+        return Err("Empty");
+    }
+
+    if !octal_str.chars().all(|c| ('0'..='7').contains(&c)) {
+        return Err("Non-octal Value");
+    }
+
+    // Convert octal to decimal and directly return the Result
+    u64::from_str_radix(octal_str, 8).map_err(|_| "Conversion error")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_empty_string() {
+        let input = "";
+        let expected = Err("Empty");
+        assert_eq!(octal_to_decimal(input), expected);
+    }
+
+    #[test]
+    fn test_invalid_octal() {
+        let input = "89";
+        let expected = Err("Non-octal Value");
+        assert_eq!(octal_to_decimal(input), expected);
+    }
+
+    #[test]
+    fn test_valid_octal() {
+        let input = "123";
+        let expected = Ok(83);
+        assert_eq!(octal_to_decimal(input), expected);
+    }
+
+    #[test]
+    fn test_valid_octal2() {
+        let input = "1234";
+        let expected = Ok(668);
+        assert_eq!(octal_to_decimal(input), expected);
+    }
+
+    #[test]
+    fn test_valid_octal3() {
+        let input = "12345";
+        let expected = Ok(5349);
+        assert_eq!(octal_to_decimal(input), expected);
+    }
+}