Code for updating a structure

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

typedef struct {
    char ramSlowFwdIndex[4];
    char ramSlowBwdIndex[4];
    char rammingShellFwdIndex[4];
    char rammingShellBwdIndex[4];
    char breechOpenIndex[4];
    char breechCloseIndex[4];
    char encoderDataIndex[4];
} fileIndexType;


void incrementIndex(char *index, int incrementValue);
void readAndUpdateFileIndex(const char *fileName, fileIndexType *fileIndex, int incrementValue, const char *variable);

int main() {
    
    FILE *file = fopen("example.txt", "w+");
    if (file == NULL) {
        printf("Error: Unable to open file for reading\n");
        return 1;
    }
    fclose(file);
    
    fileIndexType fileIndex = {"001", "001", "001", "001", "001", "001", "001"};
    readAndUpdateFileIndex("example.txt", &fileIndex, 1, "rammingShellBwdIndex"); // Increment 'rammingShellBwdIndex' value by 1


    return 0;
}




void incrementIndex(char *index, int incrementValue) {
    int value = atoi(index) + incrementValue;
    sprintf(index, "%03d", value);
}

void readAndUpdateFileIndex(const char *fileName, fileIndexType *fileIndex, int incrementValue, const char *variable) {
    FILE *file = fopen(fileName, "r+");
    if (file == NULL) {
        printf("Error: Unable to open file for reading\n");
        return 1;
    }

    fscanf(file, "%s %s %s %s %s %s %s", fileIndex->ramSlowFwdIndex, fileIndex->ramSlowBwdIndex,
           fileIndex->rammingShellFwdIndex, fileIndex->rammingShellBwdIndex,
           fileIndex->breechOpenIndex, fileIndex->breechCloseIndex, fileIndex->encoderDataIndex);

    fclose(file);

    // Increment the desired variable
    if (strcmp(variable, "ramSlowFwdIndex") == 0) {
        incrementIndex(fileIndex->ramSlowFwdIndex, incrementValue);
    } else if (strcmp(variable, "ramSlowBwdIndex") == 0) {
        incrementIndex(fileIndex->ramSlowBwdIndex, incrementValue);
    } else if (strcmp(variable, "rammingShellFwdIndex") == 0) {
        incrementIndex(fileIndex->rammingShellFwdIndex, incrementValue);
    } else if (strcmp(variable, "rammingShellBwdIndex") == 0) {
        incrementIndex(fileIndex->rammingShellBwdIndex, incrementValue);
    } else if (strcmp(variable, "breechOpenIndex") == 0) {
        incrementIndex(fileIndex->breechOpenIndex, incrementValue);
    } else if (strcmp(variable, "breechCloseIndex") == 0) {
        incrementIndex(fileIndex->breechCloseIndex, incrementValue);
    } else if (strcmp(variable, "encoderDataIndex") == 0) {
        incrementIndex(fileIndex->encoderDataIndex, incrementValue);
    } else {
        printf("Error: Invalid variable specified\n");
        return 1;
    }

    // Write updated value back to file
    file = fopen(fileName, "w");
    if (file == NULL) {
        printf("Error: Unable to open file for writing\n");
        return 1;
    }

    fprintf(file, "%s %s %s %s %s %s %s", fileIndex->ramSlowFwdIndex, fileIndex->ramSlowBwdIndex,
            fileIndex->rammingShellFwdIndex, fileIndex->rammingShellBwdIndex,
            fileIndex->breechOpenIndex, fileIndex->breechCloseIndex, fileIndex->encoderDataIndex);

    fclose(file);
}