Convert String to Integer in C programming language

In this C program, we are going to learn how to convert a string to the integer using different methods like direct, with using function and without using function?
Submitted by IncludeHelp, on May 27, 2016

Given a number as string and we have to convert it to integer using C program.

Example:

    Input: "1234" (string value)
    Output: 1234 (Integer value)

Code to Convert String to Integer in C programming

Direct Method

#include <stdio.h>

int main()
{
	unsigned char text[]="1234";
	int intValue;
	
	intValue=((text[0]-0x30)*1000)+((text[1]-0x30)*100)+((text[2]-0x30)*10)+((text[3]-0x30));
	printf("Integer value is: %d",intValue);
}

Output

Integer value is: 1234

Using atoi Function

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

int main()
{
	unsigned char text[]="1234";
	int intValue;
	
	intValue=atoi(text);
	printf("Integer value is: %d",intValue);
	
	return 0;
}

Output

Integer value is: 1234

Using sscanf Function

#include <stdio.h>

int main()
{
	unsigned char text[]="1234";
	int intValue;
	
	sscanf(text,"%04d",&intValue);
	printf("Integer value is: %d",intValue);
	
	return 0;
}

Output

    Integer value is: 1234

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