The function atoi converts a string to a integer(int). The function skips all white-space characters at the beginning of the string until the first non-whitespace character is found. Then it converts the subsequent characters into a integer number until it finds a character which is not a digit. It also takes an optional initial plus or minus sign before first base-10 digit in string.
Function prototype of atoi
int atoi(const char *str);
- str : A pointer to a string beginning with the representation of an integer number.
Return value of atoi
This function returns the converted integer number as an int value otherwise it returns zero(0), If no valid conversion could be performed.
C program using atoi function
The following program shows the use of atoi function for string to integer conversion.
#include <stdio.h>
#include <stdlib.h>
int main(){
char string[100];
int value;
printf("Enter a string\n");
scanf("%s", &string);
/* String to Integer conversion */
value = atoi(string);
printf("Integer value %d\n", value);
return 0;
}
Output
Enter a string 1234 Integer value 1234
Enter a string 1234.555 Integer value 1234
Enter a string 1234ABCD Integer value 1234
Enter a string ABCD Integer value 0