C library - log() function

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The C library log() function of type double that accept x as parameter to return the natural logarithm(base-e logarithm).

In programming, log concept is used to monitor and trouble shooting the system issues and tracking events, random user activity, and security incidents.

Syntax

Following is the syntax of the C library function log() −

double log(double x)

Parameters

This function takes only a single parameter −

• x − This is the floating point value.

Return Value

This function returns natural logarithm of x.

Example 1

Following is the C library program that shows the usage of log() function.

#include <stdio.h>
#include <math.h>

int main () {
   double x, ret;
   x = 2.7;

   /* finding log(2.7) */
   ret = log(x);
   printf("log(%lf) = %lf", x, ret);
   
   return(0);
}

Output

On execution of above code, we get the following result −

log(2.700000) = 0.993252

Example 2

The program illustrates the values of different data types using the function log().

#include <stdio.h>
#include <math.h>
   
int main() {
   double x = 10.0;
   float y = 20.9;
   int z = 100;
   long double u = 89;
   double res1 = log(x);
   float res2 = log(y);
   int res3 = log(z);
   long double res4 = log(u);
    
   printf("The log value of x %.2f = %.6f\n", x, res1);
   printf("The log value of y %.2f = %.6f\n", y, res2);
   printf("The log value of z %d = %.6f\n", z, (double)res3);
   printf("The log value of u %.2Lf = %.6Lf\n", u, res4);
   return 0;
}   

Output

After executing the code, we get the following result −

The log value of x 10.00 = 2.302585
The log value of y 20.90 = 3.039749
The log value of z 100 = 4.000000
The log value of u 89.00 = 4.488636

Example 3

Below the program calculate the sum value using log().

#include <stdio.h>
#include <math.h>

int main() {
   double x = 51.0; 
   double y = 13.0; 
   double log_x = log(x);
   double log_y = log(y);
   double sum_of_logs = log_x + log_y;

   printf("Log(%lf) + Log(%lf) = %lf\n", x, y, sum_of_logs);
   return 0;
}

Output

The above code produces the following result −

Log(51.000000) + Log(13.000000) = 6.496775