How to convert the String to Integer in C

In this tutorial, we are going to learn about how to convert the string to an integer in C.

Using atoi() function

In C, we can use the atoi() function to convert a string to an integer.

The atoi() function is available in stdlib.h library.

Here is an example, that converts the string "1011" to an integer 1011:

#include<stdio.h>
#include <stdlib.h>

int main() {
    // Converting a numeric string to integer
    char str[5] = "1011";
    int a = atoi(str);
    printf("Converting '1011': %d\n", a);
}

If a string starts with alphanumeric then the atoi() function returns 0.

Example:

#include<stdio.h>
#include <stdlib.h>

int main() {
    // Converting a numeric string to integer
    char str[5] = "olaa";
    int a = atoi(str);
    printf("Converting '1011': %d\n", a);
}

Output:

0