Converting String to Long in C

Here, we will see how to build a C Program For String to Long Conversion using strtol() function.

Syntax:

long int strtol(char *string, char **ptr, int base)

1. The first argument is given as a string
2. The second argument is a reference to an object of type char*
3. The third argument denotes the base in which the number is represented. To know more about visit strtol() function.

Note: We don’t have to use long int in the case of strtoul() because the range of unsigned long is greater than long on the positive front. 
[long : -2147483648 to 2147483647 and unsigned long : 0 to 4294967295]

Syntax:
strtoul(char *string, char **ptr, int base) // no long int need in strtoul()

C

// C program to demonstrate working of strol()
#include <stdio.h>
#include <stdlib.h>

int main()
{
    // To store Number in String form.
    char string[10] = "1234567890";
    long integer;

    // Base is 10 because we are converting to integer.
    integer = strtol(string, NULL, 10);
    printf("Number is %lu", integer);
}

Output

Number is 1234567890

C

// C program to demonstrate working of strol()
#include <stdio.h>
#include <stdlib.h>

int main()
{
    char string[40] = "100 GeeksforGeeks";
    long integer;
    char* ptr;

    // strtol function to convert number in string form to
    // long integer with base 10
    integer = strtol(string, &ptr, 10);
    printf("Integer part is %lu\n", integer);
    printf("String part is %s\n", ptr);

    return 0;
}

Output

Integer part is 100
String part is  GeeksforGeeks

Method: Using atol() function 

C

#include <stdlib.h>
#include <stdio.h>
int main()
{
    long l;
    char *str;
    str = "349639 geeksforgeeks";
    l = atol(str);
printf("l = %.ld\n",l);
}

Output

l = 349639

Method: Using ltoa() 

C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
    long i = 1234;
    char buffer[100];

    ltoa(i, buffer, 10);
    printf("string is %s\n", buffer);
    return 0;
}

Output

string is 1234

Method: Without Inbuilt Function

C

// C program to demonstrate working of strol()
#include <stdio.h>
#include <stdlib.h>

// Driver Code
int main()
{
    // To store Number in String form.
    char string[10] = "123456789";
    long integer = 0;

    int i = 0;

    // Until null character is encountered
    while (string[i] != '\0') {
        integer = (integer * 10) + (string[i] - '0');
        i++;
    }

    // Printing the number
    printf("Number is %lu", integer);
}

Output

Number is 123456789