"This program computes the logarithm base b (b > 1) of a given number x > 0. It first checks that exactly two command-line arguments are provided, then verifies that x is greater than zero and that the base is greater than one. If either condition is invalid, the program prints an error message and exits; otherwise, it calculates the result with log($x) / log($b).\n\n1 <?php\n\n2\n\n3 /**\n\n4 * This program computes the logarithm base b (b > 1)\n\n5 * of a given number x > 0\n\n6 */\n\n7\n\n8 if($argc != 3) {\n\n9 printf(\"Usage: %s b x\n\n\", $argv[0]);\n\n10 exit(1);\n\n11 }\n\n12\n\n13 $b = floatval($argv[1]);\n\n14 $x = floatval($argv[2]);\n\n15\n\n16 if($x <= 0) {\n\n17 printf(\"Error: x must be greater than zero\n\n\");\n\n18 exit(1);\n\n19 }\n\n20 if($b <= 1) {\n\n21 printf(\"Error: base must be greater than one\n\n\");\n\n22 exit(1);\n\n23 }\n\n24\n\n25 $result = log($x) / log($b);\n\n26 printf(\"log_(%f)(%f) = %f\n\n\", $b, $x, $result);\n\n27\n\n28 ?> Code Sample 38.2.: Logarithm Calculator Program in C"